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 // Created on: 2012-01-26
 // Created by: Kirill GAVRILOV
 // Copyright (c) 2012-2014 OPEN CASCADE SAS
 //
 // This file is part of Open CASCADE Technology software library.
 //
 // This library is free software; you can redistribute it and/or modify it under
 // the terms of the GNU Lesser General Public License version 2.1 as published
 // by the Free Software Foundation, with special exception defined in the file
 // OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
 // distribution for complete text of the license and disclaimer of any warranty.
 //
 // Alternatively, this file may be used under the terms of Open CASCADE
 // commercial license or contractual agreement.
 
 #ifndef OpenGl_Context_HeaderFile
 #define OpenGl_Context_HeaderFile
 
 #include <Aspect_Drawable.hxx>
 #include <Aspect_Display.hxx>
 #include <Aspect_GraphicsLibrary.hxx>
 #include <Aspect_RenderingContext.hxx>
 #include <Graphic3d_DiagnosticInfo.hxx>
 #include <Message.hxx>
 #include <OpenGl_Caps.hxx>
 #include <OpenGl_LineAttributes.hxx>
 #include <OpenGl_Material.hxx>
 #include <OpenGl_MatrixState.hxx>
 #include <OpenGl_Vec.hxx>
 #include <OpenGl_Resource.hxx>
 #include <OpenGl_TextureSet.hxx>
 #include <Standard_Transient.hxx>
 #include <TColStd_IndexedDataMapOfStringString.hxx>
 #include <TColStd_PackedMapOfInteger.hxx>
 #include <OpenGl_Clipping.hxx>
 
 #include <NCollection_Shared.hxx>
 
 #include <memory>
 
 //! Forward declarations
 #if defined(__APPLE__)
   #import <TargetConditionals.h>
   #if defined(TARGET_OS_IPHONE) && TARGET_OS_IPHONE
     #ifdef __OBJC__
       @class EAGLContext;
     #else
       struct EAGLContext;
     #endif
   #else
     #ifdef __OBJC__
       @class NSOpenGLContext;
     #else
       struct NSOpenGLContext;
     #endif
   #endif
 #endif
 
 struct OpenGl_GlFunctions;
 struct OpenGl_ArbTBO;
 struct OpenGl_ArbIns;
 struct OpenGl_ArbDbg;
 struct OpenGl_ArbFBO;
 struct OpenGl_ArbFBOBlit;
 struct OpenGl_ArbSamplerObject;
 struct OpenGl_ArbTexBindless;
 struct OpenGl_ExtGS;
 
 struct OpenGl_GlCore11Fwd;
 struct OpenGl_GlCore11;
 struct OpenGl_GlCore12;
 struct OpenGl_GlCore13;
 struct OpenGl_GlCore14;
 struct OpenGl_GlCore15;
 struct OpenGl_GlCore20;
 struct OpenGl_GlCore21;
 struct OpenGl_GlCore30;
 struct OpenGl_GlCore31;
 struct OpenGl_GlCore32;
 struct OpenGl_GlCore33;
 struct OpenGl_GlCore40;
 struct OpenGl_GlCore41;
 struct OpenGl_GlCore42;
 struct OpenGl_GlCore43;
 struct OpenGl_GlCore44;
 struct OpenGl_GlCore45;
 struct OpenGl_GlCore46;
 
 class Graphic3d_Camera;
 class Graphic3d_PresentationAttributes;
 class OpenGl_Aspects;
 class OpenGl_FrameBuffer;
 class OpenGl_ShaderProgram;
 class OpenGl_ShaderManager;
 class OpenGl_FrameStats;
 
 enum OpenGl_FeatureFlag
 {
   OpenGl_FeatureNotAvailable = 0, //!< Feature is not supported by OpenGl implementation.
   OpenGl_FeatureInExtensions = 1, //!< Feature is supported as extension.
   OpenGl_FeatureInCore       = 2  //!< Feature is supported as part of core profile.
 };
 
 DEFINE_STANDARD_HANDLE(OpenGl_Context, Standard_Transient)
 
 //! This class generalize access to the GL context and available extensions.
 //!
 //! Functions related to specific OpenGL version or extension are grouped into structures which can be accessed as fields of this class.
 //! The most simple way to check that required functionality is available - is NULL check for the group:
 //! @code
 //!   if (myContext->core20 != NULL)
 //!   {
 //!     myGlProgram = myContext->core20->glCreateProgram();
 //!     .. do more stuff ..
 //!   }
 //!   else
 //!   {
 //!     .. compatibility with outdated configurations ..
 //!   }
 //! @endcode
 //!
 //! Current implementation provide access to OpenGL core functionality up to 4.6 version (core12, core13, core14, etc.)
 //! as well as several extensions (arbTBO, arbFBO, etc.).
 //!
 //! OpenGL context might be initialized in Core Profile. In this case deprecated functionality become unavailable.
 //! To select which core** function set should be used in specific case:
 //!  - Determine the minimal OpenGL version required for implemented functionality and use it to access all functions.
 //!    For example, if algorithm requires OpenGL 2.1+, it is better to write core20fwd->glEnable() rather than core11fwd->glEnable() for uniformity.
 //!  - Validate minimal requirements at initialization/creation time and omit checks within code where algorithm should be already initialized.
 //!    Properly escape code incompatible with Core Profile. The simplest way to check Core Profile is "if (core11ffp == NULL)".
 //!
 //! Simplified extensions classification:
 //!  - prefixed with NV, AMD, ATI are vendor-specific (however may be provided by other vendors in some cases);
 //!  - prefixed with EXT are accepted by 2+ vendors;
 //!  - prefixed with ARB are accepted by Architecture Review Board and are candidates
 //!    for inclusion into GL core functionality.
 //! Some functionality can be represented in several extensions simultaneously.
 //! In this case developer should be careful because different specification may differ
 //! in aspects (like enumeration values and error-handling).
 //!
 //! Notice that some systems provide mechanisms to simultaneously incorporate with GL contexts with different capabilities.
 //! For this reason OpenGl_Context should be initialized and used for each GL context independently.
 //!
 //! Matrices of OpenGl transformations:
 //! model -> world -> view -> projection
 //! These matrices might be changed for local transformation, transform persistent using direct access to
 //! current matrix of ModelWorldState, WorldViewState and ProjectionState
 //! After, these matrices should be applied using ApplyModelWorldMatrix, ApplyWorldViewMatrix,
 //! ApplyModelViewMatrix or ApplyProjectionMatrix.
 class OpenGl_Context : public Standard_Transient
 {
   DEFINE_STANDARD_RTTIEXT(OpenGl_Context, Standard_Transient)
   friend class OpenGl_Window;
   friend struct OpenGl_GlFunctions;
 public:
 
   typedef NCollection_Shared< NCollection_DataMap<TCollection_AsciiString, Handle(OpenGl_Resource)> > OpenGl_ResourcesMap;
 
   //! Function for getting power of to number larger or equal to input number.
   //! @param theNumber    number to 'power of two'
   //! @param theThreshold upper threshold
   //! @return power of two number
   inline static Standard_Integer GetPowerOfTwo (const Standard_Integer theNumber,
                                                 const Standard_Integer theThreshold)
   {
     for (Standard_Integer p2 = 2; p2 <= theThreshold; p2 <<= 1)
     {
       if (theNumber <= p2)
       {
         return p2;
       }
     }
     return theThreshold;
   }
 
   //! Format GL constant as hex value 0xABCD.
   Standard_EXPORT static TCollection_AsciiString FormatGlEnumHex (int theGlEnum);
 
   //! Format pointer as hex value 0xABCD.
   Standard_EXPORT static TCollection_AsciiString FormatPointer (const void* thePtr);
 
   //! Format size value.
   Standard_EXPORT static TCollection_AsciiString FormatSize (Standard_Size theSize);
 
   //! Return text description of GL error.
   Standard_EXPORT static TCollection_AsciiString FormatGlError (int theGlError);
 
 public:
 
   //! Empty constructor. You should call Init() to perform initialization with bound GL context.
   Standard_EXPORT OpenGl_Context (const Handle(OpenGl_Caps)& theCaps = NULL);
 
   //! Destructor.
   Standard_EXPORT virtual ~OpenGl_Context();
 
   //! Release all resources, including shared ones
   Standard_EXPORT void forcedRelease();
 
   //! Share GL context resources.
   //! theShareCtx - handle to context to retrieve handles to shared resources.
   Standard_EXPORT void Share (const Handle(OpenGl_Context)& theShareCtx);
 
   //! Initialize class from currently bound OpenGL context. Method should be called only once.
   //! @return false if no GL context is bound to the current thread
   Standard_EXPORT Standard_Boolean Init (const Standard_Boolean theIsCoreProfile = Standard_False);
 
   //! @return true if this context is valid (has been initialized)
   inline Standard_Boolean IsValid() const
   {
     return myIsInitialized;
   }
 
   //! Initialize class from specified surface and rendering context. Method should be called only once.
   //! The meaning of parameters is platform-specific.
   //!
   //! EGL:
   //! @code
   //!   Handle(Aspect_Window) theAspWin;
   //!   EGLSurface theEglSurf = eglCreateWindowSurface (theEglDisp, anEglConfig, (EGLNativeWindowType )theAspWin->NativeHandle(), NULL);
   //!   EGLDisplay theEglDisp = eglGetDisplay (EGL_DEFAULT_DISPLAY);
   //!   EGLContext theEglCtx  = eglCreateContext ((EGLDisplay )theEglDisp, anEglConfig, EGL_NO_CONTEXT, anEglCtxAttribs);
   //!   Handle(OpenGl_Context) aGlCtx = new OpenGl_Context();
   //!   aGlCtx->Init ((Aspect_Drawable )theEglSurf, (Aspect_Display )theEglDisp,  (Aspect_RenderingContext )theEglCtx);
   //! @endcode
   //!
   //! Windows (Win32):
   //! @code
   //!   Handle(WNT_Window) theAspWin;
   //!   HWND  theWindow   = (HWND )theAspWin->NativeHandle();
   //!   HDC   theDevCtx   = GetDC(theWindow);
   //!   HGLRC theGContext = wglCreateContext (theDevCtx);
   //!   Handle(OpenGl_Context) aGlCtx = new OpenGl_Context();
   //!   aGlCtx->Init ((Aspect_Drawable )theWindow, (Aspect_Display )theDevCtx, (Aspect_RenderingContext )theGContext);
   //! @endcode
   //!
   //! Linux (Xlib):
   //! @code
   //!   Handle(Xw_Window) theAspWin;
   //!   Window     theXWindow = (Window )theAspWin->NativeHandle();
   //!   Display*   theXDisp   = (Display* )theAspWin->DisplayConnection()->GetDisplayAspect();
   //!   GLXContext theGlxCtx  = glXCreateContext (theXDisp, aVis.get(), NULL, GL_TRUE);
   //!   Handle(OpenGl_Context) aGlCtx = new OpenGl_Context();
   //!   aGlCtx->Init ((Aspect_Drawable )theXWindow, (Aspect_Display )theXDisp,  (Aspect_RenderingContext )theGlxCtx);
   //! @endcode
   //!
   //! @param theSurface [in] surface / window          (EGLSurface | HWND  | GLXDrawable/Window)
   //! @param theDisplay [in] display or device context (EGLDisplay | HDC   | Display*)
   //! @param theContext [in] rendering context         (EGLContext | HGLRC | GLXContext | EAGLContext* | NSOpenGLContext*)
   //! @param theIsCoreProfile [in] flag indicating that passed GL rendering context has been created with Core Profile
   //! @return false if OpenGL context can not be bound to specified surface
   Standard_EXPORT Standard_Boolean Init (const Aspect_Drawable         theSurface,
                                          const Aspect_Display          theDisplay,
                                          const Aspect_RenderingContext theContext,
                                          const Standard_Boolean        theIsCoreProfile = Standard_False);
 
   //! Return window handle currently bound to this OpenGL context (EGLSurface | HWND | GLXDrawable).
   Aspect_Drawable Window() const { return myWindow; }
 
   //! Return display / window device context (EGLDisplay | HDC | Display*).
   Aspect_Display GetDisplay() const { return myDisplay; }
 
   //! Return rendering context (EGLContext | HGLRC | GLXContext | EAGLContext* | NSOpenGLContext*).
   Aspect_RenderingContext RenderingContext() const { return myGContext; }
 
 #if defined(__APPLE__) && !defined(HAVE_XLIB)
   #if defined(TARGET_OS_IPHONE) && TARGET_OS_IPHONE
 
   //! Initialize class from specified OpenGL ES context (EAGLContext). Method should be called only once.
   Standard_Boolean Init (EAGLContext*           theGContext,
                          const Standard_Boolean theIsCoreProfile = Standard_False)
   {
     return Init ((Aspect_Drawable )0, (Aspect_Display )0, (Aspect_RenderingContext )theGContext, theIsCoreProfile);
   }
   #else
   //! Initialize class from specified OpenGL context (NSOpenGLContext). Method should be called only once.
   Standard_Boolean Init (NSOpenGLContext*       theGContext,
                          const Standard_Boolean theIsCoreProfile = Standard_False)
   {
     return Init ((Aspect_Drawable )0, (Aspect_Display )0, (Aspect_RenderingContext )theGContext, theIsCoreProfile);
   }
   #endif
 #endif
 
   //! Read OpenGL version information from active context.
   Standard_EXPORT static void ReadGlVersion (Standard_Integer& theGlVerMajor,
                                              Standard_Integer& theGlVerMinor);
 
   //! Check if theExtName extension is supported by active GL context.
   Standard_EXPORT Standard_Boolean CheckExtension (const char* theExtName) const;
 
   //! Check if theExtName extension is in extensions string.
   Standard_EXPORT static Standard_Boolean CheckExtension (const char* theExtString,
                                                           const char* theExtName);
 
   //! Auxiliary template to retrieve GL function pointer.
   //! Pointer to function retrieved from library is statically casted
   //! to requested type - there no way to check real signature of exported function.
   //! The context should be bound before call.
   //! @param theLastFailFuncName [out] set to theFuncName in case of failure, unmodified on success
   //! @param theFuncName [in] function name to find
   //! @param theFuncPtr [out] retrieved function pointer
   //! @return TRUE on success
   template <typename FuncType_t>
   Standard_Boolean FindProcVerbose (const char*& theLastFailFuncName,
                                     const char* theFuncName,
                                     FuncType_t& theFuncPtr)
   {
     theFuncPtr = (FuncType_t )findProc (theFuncName);
     if (theFuncPtr == NULL)
     {
       theLastFailFuncName = theFuncName;
       return Standard_False;
     }
     return Standard_True;
   }
 
   //! Auxiliary template to retrieve GL function pointer.
   //! Same as FindProcVerbose() but without auxiliary last function name argument.
   template <typename FuncType_t>
   Standard_Boolean FindProc (const char* theFuncName,
                              FuncType_t& theFuncPtr)
   {
     theFuncPtr = (FuncType_t )findProc (theFuncName);
     return (theFuncPtr != NULL);
   }
 
   //! Return active graphics library.
   Aspect_GraphicsLibrary GraphicsLibrary() const { return myGapi; }
 
   //! @return true if detected GL version is greater or equal to requested one.
   inline Standard_Boolean IsGlGreaterEqual (const Standard_Integer theVerMajor,
                                             const Standard_Integer theVerMinor) const
   {
     return (myGlVerMajor >  theVerMajor)
         || (myGlVerMajor == theVerMajor && myGlVerMinor >= theVerMinor);
   }
 
   //! Return cached GL version major number.
   Standard_Integer VersionMajor() const { return myGlVerMajor; }
 
   //! Return cached GL version minor number.
   Standard_Integer VersionMinor() const { return myGlVerMinor; }
 
   //! Access entire map of loaded OpenGL functions.
   const OpenGl_GlFunctions* Functions() const { return myFuncs.get(); }
 
   //! Clean up errors stack for this GL context (glGetError() in loop).
   //! @return true if some error has been cleared
   Standard_EXPORT bool ResetErrors (const bool theToPrintErrors = false);
 
   //! This method uses system-dependent API to retrieve information
   //! about GL context bound to the current thread.
   //! @return true if current thread is bound to this GL context
   Standard_EXPORT Standard_Boolean IsCurrent() const;
 
   //! Activates current context.
   //! Class should be initialized with appropriate info.
   Standard_EXPORT Standard_Boolean MakeCurrent();
 
   //! Swap front/back buffers for this GL context (should be activated before!).
   Standard_EXPORT void SwapBuffers();
 
   //! Setup swap interval (VSync).
   Standard_EXPORT Standard_Boolean SetSwapInterval (const Standard_Integer theInterval);
 
   //! Return true if active mode is GL_RENDER (cached state)
   Standard_EXPORT Standard_Boolean IsRender() const;
 
   //! Return true if active mode is GL_FEEDBACK (cached state)
   Standard_EXPORT Standard_Boolean IsFeedback() const;
 
   //! This function retrieves information from GL about free GPU memory that is:
   //!  - OS-dependent. On some OS it is per-process and on others - for entire system.
   //!  - Vendor-dependent. Currently available only on NVIDIA and AMD/ATi drivers only.
   //!  - Numbers meaning may vary.
   //! You should use this info only for diagnostics purposes.
   //! @return free GPU dedicated memory in bytes.
   Standard_EXPORT Standard_Size AvailableMemory() const;
 
   //! This function retrieves information from GL about GPU memory
   //! and contains more vendor-specific values than AvailableMemory().
   Standard_EXPORT TCollection_AsciiString MemoryInfo() const;
 
   //! This function retrieves information from GL about GPU memory.
   Standard_EXPORT void MemoryInfo (TColStd_IndexedDataMapOfStringString& theDict) const;
 
   //! Fill in the dictionary with OpenGL info.
   //! Should be called with bound context.
   Standard_EXPORT void DiagnosticInformation (TColStd_IndexedDataMapOfStringString& theDict,
                                               Graphic3d_DiagnosticInfo theFlags) const;
 
   //! Fetches information about window buffer pixel format.
   Standard_EXPORT void WindowBufferBits (Graphic3d_Vec4i& theColorBits,
                                          Graphic3d_Vec2i& theDepthStencilBits) const;
 
   //! Access shared resource by its name.
   //! @param  theKey - unique identifier;
   //! @return handle to shared resource or NULL.
   Standard_EXPORT const Handle(OpenGl_Resource)& GetResource (const TCollection_AsciiString& theKey) const;
 
   //! Access shared resource by its name.
   //! @param  theKey   - unique identifier;
   //! @param  theValue - handle to fill;
   //! @return true if resource was shared.
   template<typename TheHandleType>
   Standard_Boolean GetResource (const TCollection_AsciiString& theKey,
                                 TheHandleType&                 theValue) const
   {
     const Handle(OpenGl_Resource)& aResource = GetResource (theKey);
     if (aResource.IsNull())
     {
       return Standard_False;
     }
 
     theValue = TheHandleType::DownCast (aResource);
     return !theValue.IsNull();
   }
 
   //! Register shared resource.
   //! Notice that after registration caller shouldn't release it by himself -
   //! it will be automatically released on context destruction.
   //! @param theKey      - unique identifier, shouldn't be empty;
   //! @param theResource - new resource to register, shouldn't be NULL.
   Standard_EXPORT Standard_Boolean ShareResource (const TCollection_AsciiString& theKey,
                                                   const Handle(OpenGl_Resource)& theResource);
 
   //! Release shared resource.
   //! If there are more than one reference to this resource
   //! (also used by some other existing object) then call will be ignored.
   //! This means that current object itself should nullify handle before this call.
   //! Notice that this is unrecommended operation at all and should be used
   //! only in case of fat resources to release memory for other needs.
   //! @param theKey     unique identifier
   //! @param theToDelay postpone release until next redraw call
   Standard_EXPORT void ReleaseResource (const TCollection_AsciiString& theKey,
                                         const Standard_Boolean         theToDelay = Standard_False);
 
   //! Append resource to queue for delayed clean up.
   //! Resources in this queue will be released at next redraw call.
   template <class T>
   void DelayedRelease (Handle(T)& theResource)
   {
     myUnusedResources->Prepend (theResource);
     theResource.Nullify();
   }
 
   //! Clean up the delayed release queue.
   Standard_EXPORT void ReleaseDelayed();
 
   //! Return map of shared resources.
   const OpenGl_ResourcesMap& SharedResources() const { return *mySharedResources; }
 
   //! @return tool for management of clippings within this context.
   inline OpenGl_Clipping& ChangeClipping() { return myClippingState; }
 
   //! @return tool for management of clippings within this context.
   inline const OpenGl_Clipping& Clipping() const { return myClippingState; }
 
   //! @return tool for management of shader programs within this context.
   inline const Handle(OpenGl_ShaderManager)& ShaderManager() const { return myShaderManager; }
 
 public:
 
   //! Either GL_CLAMP_TO_EDGE (1.2+) or GL_CLAMP (1.1).
   Standard_Integer TextureWrapClamp() const { return myTexClamp; }
 
   //! @return true if texture parameters GL_TEXTURE_BASE_LEVEL/GL_TEXTURE_MAX_LEVEL are supported.
   Standard_Boolean HasTextureBaseLevel() const
   {
     return myGapi == Aspect_GraphicsLibrary_OpenGLES
          ? IsGlGreaterEqual (3, 0)
          : IsGlGreaterEqual (1, 2);
   }
 
   //! Return map of supported texture formats.
   const Handle(Image_SupportedFormats)& SupportedTextureFormats() const { return mySupportedFormats; }
 
   //! @return maximum degree of anisotropy texture filter
   Standard_Integer MaxDegreeOfAnisotropy() const { return myAnisoMax; }
 
   //! @return value for GL_MAX_TEXTURE_SIZE
   Standard_Integer MaxTextureSize() const { return myMaxTexDim; }
 
   //! @return value for GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS
   Standard_Integer MaxCombinedTextureUnits() const { return myMaxTexCombined; }
 
   //! This method returns the multi-texture limit for obsolete fixed-function pipeline.
   //! Use MaxCombinedTextureUnits() instead for limits for using programmable pipeline.
   //! @return value for GL_MAX_TEXTURE_UNITS
   Standard_Integer MaxTextureUnitsFFP() const { return myMaxTexUnitsFFP; }
 
   //! Return texture unit to be used for sprites (Graphic3d_TextureUnit_PointSprite by default).
   Graphic3d_TextureUnit SpriteTextureUnit() const { return mySpriteTexUnit; }
 
   //! @return true if MSAA textures are supported.
   Standard_Boolean HasTextureMultisampling() const { return myHasMsaaTextures; }
 
   //! @return value for GL_MAX_SAMPLES
   Standard_Integer MaxMsaaSamples() const { return myMaxMsaaSamples; }
 
   //! @return maximum FBO width for image dump
   Standard_Integer MaxDumpSizeX() const { return myMaxDumpSizeX; }
 
   //! @return maximum FBO height for image dump
   Standard_Integer MaxDumpSizeY() const { return myMaxDumpSizeY; }
 
   //! @return value for GL_MAX_DRAW_BUFFERS
   Standard_Integer MaxDrawBuffers() const { return myMaxDrawBuffers; }
 
   //! @return value for GL_MAX_COLOR_ATTACHMENTS
   Standard_Integer MaxColorAttachments() const { return myMaxColorAttachments; }
 
   //! Get maximum number of clip planes supported by OpenGl.
   //! This value is implementation dependent. At least 6
   //! planes should be supported by OpenGl (see specs).
   //! @return value for GL_MAX_CLIP_PLANES
   Standard_Integer MaxClipPlanes() const { return myMaxClipPlanes; }
 
   //! @return TRUE if ray tracing mode is supported
   Standard_Boolean HasRayTracing() const { return myHasRayTracing; }
 
   //! @return TRUE if textures in ray tracing mode are supported
   Standard_Boolean HasRayTracingTextures() const { return myHasRayTracingTextures; }
 
   //! @return TRUE if adaptive screen sampling in ray tracing mode is supported
   Standard_Boolean HasRayTracingAdaptiveSampling() const { return myHasRayTracingAdaptiveSampling; }
 
   //! @return TRUE if atomic adaptive screen sampling in ray tracing mode is supported
   Standard_Boolean HasRayTracingAdaptiveSamplingAtomic() const { return myHasRayTracingAdaptiveSamplingAtomic; }
 
   //! Returns TRUE if sRGB rendering is supported.
   bool HasSRGB() const
   {
     return hasTexSRGB
        &&  hasFboSRGB;
   }
 
   //! Returns TRUE if sRGB rendering is supported and permitted.
   bool ToRenderSRGB() const
   {
     return HasSRGB()
        && !caps->sRGBDisable
        && !caps->ffpEnable;
   }
 
   //! Returns TRUE if window/surface buffer is sRGB-ready.
   //!
   //! When offscreen FBOs are created in sRGB, but window is not sRGB-ready,
   //! blitting into window should be done with manual gamma correction.
   //!
   //! In desktop OpenGL, window buffer can be considered as sRGB-ready by default,
   //! even when application has NOT requested sRGB-ready pixel format,
   //! and rendering is managed via GL_FRAMEBUFFER_SRGB state.
   //!
   //! In OpenGL ES, sRGB-ready window surface should be explicitly requested on construction,
   //! and cannot be disabled/enabled without GL_EXT_sRGB_write_control extension afterwards
   //! (GL_FRAMEBUFFER_SRGB can be considered as always tuned ON).
   bool IsWindowSRGB() const { return myIsSRgbWindow; }
 
   //! Overrides if window/surface buffer is sRGB-ready or not (initialized with the context).
   void SetWindowSRGB (bool theIsSRgb) { myIsSRgbWindow = theIsSRgb; }
 
   //! Returns TRUE if window/surface buffer has deep color (10bit per component / 30bit RGB) or better precision.
   bool IsWindowDeepColor() const { return myIsWindowDeepColor; }
 
   //! Convert Quantity_ColorRGBA into vec4
   //! with conversion or no conversion into non-linear sRGB
   //! basing on ToRenderSRGB() flag.
   OpenGl_Vec4 Vec4FromQuantityColor (const OpenGl_Vec4& theColor) const
   {
     return myIsSRgbActive
          ? Vec4LinearFromQuantityColor(theColor)
          : Vec4sRGBFromQuantityColor  (theColor);
   }
 
   //! Convert Quantity_ColorRGBA into vec4.
   //! Quantity_Color is expected to be linear RGB, hence conversion is NOT required
   const OpenGl_Vec4& Vec4LinearFromQuantityColor (const OpenGl_Vec4& theColor) const { return theColor; }
 
   //! Convert Quantity_ColorRGBA (linear RGB) into non-linear sRGB vec4.
   OpenGl_Vec4 Vec4sRGBFromQuantityColor (const OpenGl_Vec4& theColor) const
   {
     return Quantity_ColorRGBA::Convert_LinearRGB_To_sRGB (theColor);
   }
 
   //! Returns TRUE if PBR shading model is supported.
   //! Basically, feature requires OpenGL 3.0+ / OpenGL ES 3.0+ hardware; more precisely:
   //! - Graphics hardware with moderate capabilities for compiling long enough GLSL program.
   //! - FBO (e.g. for baking environment).
   //! - Multi-texturing with >= 4 units (LUT and IBL textures).
   //! - GL_RG32F texture format (arbTexRG + arbTexFloat)
   //! - Cubemap texture lookup textureCubeLod()/textureLod() with LOD index within Fragment Shader,
   //!   which requires GLSL OpenGL 3.0+ / OpenGL ES 3.0+ or OpenGL 2.1 + GL_EXT_gpu_shader4 extension.
   Standard_Boolean HasPBR() const { return myHasPBR; }
 
   //! Returns texture unit where Environment Lookup Table is expected to be bound, or 0 if PBR is unavailable.
   Graphic3d_TextureUnit PBREnvLUTTexUnit() const { return myPBREnvLUTTexUnit; }
 
   //! Returns texture unit where Diffuse (irradiance) IBL map's spherical harmonics coefficients is expected to be bound, or 0 if PBR is unavailable.
   Graphic3d_TextureUnit PBRDiffIBLMapSHTexUnit() const { return myPBRDiffIBLMapSHTexUnit; }
 
   //! Returns texture unit where Specular IBL map is expected to be bound, or 0 if PBR is unavailable.
   Graphic3d_TextureUnit PBRSpecIBLMapTexUnit() const { return myPBRSpecIBLMapTexUnit; }
 
   //! Returns texture unit where shadow map is expected to be bound, or 0 if unavailable.
   Graphic3d_TextureUnit ShadowMapTexUnit() const { return myShadowMapTexUnit; }
 
   //! Returns texture unit for occDepthPeelingDepth within enabled Depth Peeling.
   Graphic3d_TextureUnit DepthPeelingDepthTexUnit() const { return myDepthPeelingDepthTexUnit; }
 
   //! Returns texture unit for occDepthPeelingFrontColor within enabled Depth Peeling.
   Graphic3d_TextureUnit DepthPeelingFrontColorTexUnit() const { return myDepthPeelingFrontColorTexUnit; }
 
   //! Returns true if VBO is supported and permitted.
   inline bool ToUseVbo() const
   {
     return core15fwd != NULL
        && !caps->vboDisable;
   }
 
   //! @return cached state of GL_NORMALIZE.
   Standard_Boolean IsGlNormalizeEnabled() const { return myIsGlNormalizeEnabled; }
 
   //! Sets GL_NORMALIZE enabled or disabled.
   //! @return old value of the flag
   Standard_EXPORT Standard_Boolean SetGlNormalizeEnabled (Standard_Boolean isEnabled);
 
   //! @return cached state of polygon rasterization mode (glPolygonMode()).
   Standard_Integer PolygonMode() const { return myPolygonMode; }
 
   //! Sets polygon rasterization mode (glPolygonMode() function).
   //! @return old value of the rasterization mode.
   Standard_EXPORT Standard_Integer SetPolygonMode (const Standard_Integer theMode);
 
   //! @return cached enabled state of polygon hatching rasterization.
   bool IsPolygonHatchEnabled() const { return myHatchIsEnabled; }
 
   //! Sets enabled state of polygon hatching rasterization
   //! without affecting currently selected hatching pattern.
   //! @return previous state of polygon hatching mode.
   Standard_EXPORT bool SetPolygonHatchEnabled (const bool theIsEnabled);
 
   //! @return cached state of polygon hatch type.
   Standard_Integer PolygonHatchStyle() const { return myActiveHatchType; }
 
   //! Sets polygon hatch pattern.
   //! Zero-index value is a default alias for solid filling.
   //! @param theStyle type of hatch supported by base implementation of
   //! OpenGl_LineAttributes (Aspect_HatchStyle) or the type supported by custom
   //! implementation derived from OpenGl_LineAttributes class.
   //! @return old type of hatch.
   Standard_EXPORT Standard_Integer SetPolygonHatchStyle (const Handle(Graphic3d_HatchStyle)& theStyle);
 
   //! Sets and applies current polygon offset.
   Standard_EXPORT void SetPolygonOffset (const Graphic3d_PolygonOffset& theOffset);
 
   //! Returns currently applied polygon offset parameters.
   const Graphic3d_PolygonOffset& PolygonOffset() const { return myPolygonOffset; }
 
   //! Returns camera object.
   const Handle(Graphic3d_Camera)& Camera() const { return myCamera; }
 
   //! Sets camera object to the context and update matrices.
   Standard_EXPORT void SetCamera (const Handle(Graphic3d_Camera)& theCamera);
 
   //! Applies matrix into shader manager stored in ModelWorldState to OpenGl.
   //! In "model -> world -> view -> projection" it performs:
   //!     model -> world
   Standard_EXPORT void ApplyModelWorldMatrix();
 
   //! Applies matrix stored in WorldViewState to OpenGl.
   //! In "model -> world -> view -> projection" it performs:
   //!     model -> world -> view,
   //! where model -> world is identical matrix
   Standard_EXPORT void ApplyWorldViewMatrix();
 
   //! Applies combination of matrices stored in ModelWorldState and WorldViewState to OpenGl.
   //! In "model -> world -> view -> projection" it performs:
   //!     model -> world -> view
   Standard_EXPORT void ApplyModelViewMatrix();
 
   //! Applies matrix stored in ProjectionState to OpenGl.
   //! In "model -> world -> view -> projection" it performs:
   //!                       view -> projection
   Standard_EXPORT void ApplyProjectionMatrix();
 
 public:
 
   //! @return messenger instance
   inline const Handle(Message_Messenger)& Messenger() const
   {
     return ::Message::DefaultMessenger();
   }
 
   //! Callback for GL_ARB_debug_output extension
   //! @param theSource   message source   within GL_DEBUG_SOURCE_   enumeration
   //! @param theType     message type     within GL_DEBUG_TYPE_     enumeration
   //! @param theId       message ID       within source
   //! @param theSeverity message severity within GL_DEBUG_SEVERITY_ enumeration
   //! @param theMessage  the message itself
   Standard_EXPORT void PushMessage (const unsigned int theSource,
                                     const unsigned int theType,
                                     const unsigned int theId,
                                     const unsigned int theSeverity,
                                     const TCollection_ExtendedString& theMessage);
 
   //! Adds a filter for messages with theId and theSource (GL_DEBUG_SOURCE_)
   Standard_EXPORT Standard_Boolean ExcludeMessage (const unsigned int theSource,
                                                    const unsigned int theId);
 
   //! Removes a filter for messages with theId and theSource (GL_DEBUG_SOURCE_)
   Standard_EXPORT Standard_Boolean IncludeMessage (const unsigned int theSource,
                                                    const unsigned int theId);
 
   //! @return true if OpenGl context supports left and right rendering buffers.
   Standard_Boolean HasStereoBuffers() const { return myIsStereoBuffers; }
 
 public: //! @name methods to alter or retrieve current state
 
   //! Return structure holding frame statistics.
   const Handle(OpenGl_FrameStats)& FrameStats() const { return myFrameStats; }
 
   //! Set structure holding frame statistics.
   //! This call makes sense only if application defines OpenGl_FrameStats sub-class.
   void SetFrameStats (const Handle(OpenGl_FrameStats)& theStats) { myFrameStats = theStats; }
 
   //! Return cached viewport definition (x, y, width, height).
   const Standard_Integer* Viewport() const { return myViewport; }
 
   //! Resize the viewport (alias for glViewport).
   //! @param theRect viewport definition (x, y, width, height)
   Standard_EXPORT void ResizeViewport (const Standard_Integer theRect[4]);
 
   //! Return virtual viewport definition (x, y, width, height).
   const Standard_Integer* VirtualViewport() const { return myViewportVirt; }
 
   //! Return active read buffer.
   Standard_Integer ReadBuffer() { return myReadBuffer; }
 
   //! Switch read buffer, wrapper for ::glReadBuffer().
   Standard_EXPORT void SetReadBuffer (const Standard_Integer theReadBuffer);
 
   //! Return active draw buffer attached to a render target referred by index (layout location).
   Standard_Integer DrawBuffer (Standard_Integer theIndex = 0) const
   {
     return theIndex >= myDrawBuffers.Lower()
         && theIndex <= myDrawBuffers.Upper()
          ? myDrawBuffers.Value (theIndex)
          : 0; // GL_NONE
   }
 
   //! Switch draw buffer, wrapper for ::glDrawBuffer().
   Standard_EXPORT void SetDrawBuffer (const Standard_Integer theDrawBuffer);
 
   //! Switch draw buffer, wrapper for ::glDrawBuffers (GLsizei, const GLenum*).
   Standard_EXPORT void SetDrawBuffers (const Standard_Integer theNb, const Standard_Integer* theDrawBuffers);
 
   //! Switch read/draw buffers.
   void SetReadDrawBuffer (const Standard_Integer theBuffer)
   {
     SetReadBuffer (theBuffer);
     SetDrawBuffer (theBuffer);
   }
 
   //! Returns cached GL_FRAMEBUFFER_SRGB state.
   //! If TRUE, GLSL program is expected to write linear RGB color.
   //! Otherwise, GLSL program might need manually converting result color into sRGB color space.
   bool IsFrameBufferSRGB() const { return myIsSRgbActive; }
 
   //! Enables/disables GL_FRAMEBUFFER_SRGB flag.
   //! This flag can be set to:
   //! - TRUE when writing into offscreen FBO (always expected to be in sRGB or RGBF formats).
   //! - TRUE when writing into sRGB-ready window buffer (might require choosing proper pixel format on window creation).
   //! - FALSE if sRGB rendering is not supported or sRGB-not-ready window buffer is used for drawing.
   //! @param[in] theIsFbo flag indicating writing into offscreen FBO (always expected sRGB-ready when sRGB FBO is supported)
   //!                     or into window buffer (FALSE, sRGB-readiness might vary).
   //! @param[in] theIsFboSRgb flag indicating off-screen FBO is sRGB-ready
   Standard_EXPORT void SetFrameBufferSRGB (bool theIsFbo, bool theIsFboSRgb = true);
 
   //! Return cached flag indicating writing into color buffer is enabled or disabled (glColorMask).
   const NCollection_Vec4<bool>& ColorMaskRGBA() const { return myColorMask; }
 
   //! Enable/disable writing into color buffer (wrapper for glColorMask).
   Standard_EXPORT void SetColorMaskRGBA (const NCollection_Vec4<bool>& theToWriteColor);
 
   //! Return cached flag indicating writing into color buffer is enabled or disabled (glColorMask).
   bool ColorMask() const { return myColorMask.r(); }
 
   //! Enable/disable writing into color buffer (wrapper for glColorMask).
   //! Alpha component writes will be disabled unconditionally in case of caps->buffersOpaqueAlpha.
   Standard_EXPORT bool SetColorMask (bool theToWriteColor);
 
   //! Return TRUE if GL_SAMPLE_ALPHA_TO_COVERAGE usage is allowed.
   bool AllowSampleAlphaToCoverage() const { return myAllowAlphaToCov; }
 
   //! Allow GL_SAMPLE_ALPHA_TO_COVERAGE usage.
   void SetAllowSampleAlphaToCoverage (bool theToEnable) { myAllowAlphaToCov = theToEnable; }
 
   //! Return GL_SAMPLE_ALPHA_TO_COVERAGE state.
   bool SampleAlphaToCoverage() const { return myAlphaToCoverage; }
 
   //! Enable/disable GL_SAMPLE_ALPHA_TO_COVERAGE.
   Standard_EXPORT bool SetSampleAlphaToCoverage (bool theToEnable);
 
   //! Return back face culling state.
   Graphic3d_TypeOfBackfacingModel FaceCulling() const { return myFaceCulling; }
 
   //! Enable or disable back face culling (glEnable (GL_CULL_FACE)).
   Standard_EXPORT void SetFaceCulling (Graphic3d_TypeOfBackfacingModel theMode);
 
   //! Return back face culling state.
   bool ToCullBackFaces() const { return myFaceCulling == Graphic3d_TypeOfBackfacingModel_BackCulled; }
 
   //! Enable or disable back face culling (glCullFace() + glEnable(GL_CULL_FACE)).
   void SetCullBackFaces (bool theToEnable)
   {
     SetFaceCulling (theToEnable ? Graphic3d_TypeOfBackfacingModel_BackCulled : Graphic3d_TypeOfBackfacingModel_DoubleSided);
   }
 
   //! Fetch OpenGl context state. This class tracks value of several OpenGl
   //! state variables. Consulting the cached values is quicker than
   //! doing the same via OpenGl API. Call this method if any of the controlled
   //! OpenGl state variables has a possibility of being out-of-date.
   Standard_EXPORT void FetchState();
 
   //! @return active textures
   const Handle(OpenGl_TextureSet)& ActiveTextures() const { return myActiveTextures; }
 
   //! Bind specified texture set to current context taking into account active GLSL program.
   Standard_DEPRECATED("BindTextures() with explicit GLSL program should be used instead")
   Handle(OpenGl_TextureSet) BindTextures (const Handle(OpenGl_TextureSet)& theTextures)
   {
     return BindTextures (theTextures, myActiveProgram);
   }
 
   //! Bind specified texture set to current context, or unbind previous one when NULL specified.
   //! @param theTextures [in] texture set to bind
   //! @param theProgram  [in] program attributes; when not NULL,
   //!                         mock textures will be bound to texture units expected by GLSL program, but undefined by texture set
   //! @return previous texture set
   Standard_EXPORT Handle(OpenGl_TextureSet) BindTextures (const Handle(OpenGl_TextureSet)& theTextures,
                                                           const Handle(OpenGl_ShaderProgram)& theProgram);
 
   //! @return active GLSL program
   const Handle(OpenGl_ShaderProgram)& ActiveProgram() const
   {
     return myActiveProgram;
   }
 
   //! Bind specified program to current context,
   //! or unbind previous one when NULL specified.
   //! @return true if some program is bound to context
   Standard_EXPORT Standard_Boolean BindProgram (const Handle(OpenGl_ShaderProgram)& theProgram);
 
   //! Setup current shading material.
   Standard_EXPORT void SetShadingMaterial (const OpenGl_Aspects* theAspect,
                                            const Handle(Graphic3d_PresentationAttributes)& theHighlight);
 
   //! Checks if transparency is required for the given aspect and highlight style.
   Standard_EXPORT static Standard_Boolean CheckIsTransparent (const OpenGl_Aspects* theAspect,
                                                               const Handle(Graphic3d_PresentationAttributes)& theHighlight,
                                                               Standard_ShortReal& theAlphaFront,
                                                               Standard_ShortReal& theAlphaBack);
 
   //! Checks if transparency is required for the given aspect and highlight style.
   static Standard_Boolean CheckIsTransparent (const OpenGl_Aspects* theAspect,
                                               const Handle(Graphic3d_PresentationAttributes)& theHighlight)
   {
     Standard_ShortReal anAlphaFront = 1.0f, anAlphaBack = 1.0f;
     return CheckIsTransparent (theAspect, theHighlight, anAlphaFront, anAlphaBack);
   }
 
   //! Setup current color.
   Standard_EXPORT void SetColor4fv (const OpenGl_Vec4& theColor);
 
   //! Setup type of line.
   Standard_EXPORT void SetTypeOfLine (const Aspect_TypeOfLine  theType,
                                       const Standard_ShortReal theFactor = 1.0f);
 
   //! Setup stipple line pattern with 1.0f factor; wrapper for glLineStipple().
   void SetLineStipple (const uint16_t thePattern) { SetLineStipple (1.0f, thePattern); }
 
   //! Setup type of line; wrapper for glLineStipple().
   Standard_EXPORT void SetLineStipple (const Standard_ShortReal theFactor,
                                        const uint16_t thePattern);
 
   //! Setup width of line.
   Standard_EXPORT void SetLineWidth (const Standard_ShortReal theWidth);
 
   //! Setup point size.
   Standard_EXPORT void SetPointSize (const Standard_ShortReal theSize);
 
   //! Setup point sprite origin using GL_POINT_SPRITE_COORD_ORIGIN state:
   //! - GL_UPPER_LEFT when GLSL program is active;
   //!   flipping should be handled in GLSL program for compatibility with OpenGL ES
   //! - GL_LOWER_LEFT for FFP
   Standard_EXPORT void SetPointSpriteOrigin();
 
   //! Setup texture matrix to active GLSL program or to FFP global state using glMatrixMode (GL_TEXTURE).
   //! @param theParams    [in] texture parameters
   //! @param theIsTopDown [in] texture top-down flag
   Standard_EXPORT void SetTextureMatrix (const Handle(Graphic3d_TextureParams)& theParams,
                                          const Standard_Boolean theIsTopDown);
 
   //! Bind default Vertex Array Object
   Standard_EXPORT void BindDefaultVao();
 
   //! Default Frame Buffer Object.
   const Handle(OpenGl_FrameBuffer)& DefaultFrameBuffer() const
   {
     return myDefaultFbo;
   }
 
   //! Setup new Default Frame Buffer Object and return previously set.
   //! This call doesn't change Active FBO!
   Standard_EXPORT Handle(OpenGl_FrameBuffer) SetDefaultFrameBuffer (const Handle(OpenGl_FrameBuffer)& theFbo);
 
   //! Return debug context initialization state.
   Standard_Boolean IsDebugContext() const
   {
     return myIsGlDebugCtx;
   }
 
   Standard_EXPORT void EnableFeatures() const;
 
   Standard_EXPORT void DisableFeatures() const;
 
   //! Return resolution for rendering text.
   unsigned int Resolution() const { return myResolution; }
 
   //! Resolution scale factor (rendered resolution to standard resolution).
   //! This scaling factor for parameters like text size to be properly displayed on device (screen / printer).
   Standard_ShortReal ResolutionRatio() const { return myResolutionRatio; }
 
   //! Rendering scale factor (rendering viewport height to real window buffer height).
   Standard_ShortReal RenderScale() const { return myRenderScale; }
 
   //! Return TRUE if rendering scale factor is not 1.
   Standard_Boolean HasRenderScale() const { return Abs (myRenderScale - 1.0f) > 0.0001f; }
 
   //! Rendering scale factor (inverted value).
   Standard_ShortReal RenderScaleInv() const { return myRenderScaleInv; }
 
   //! Return scale factor for line width.
   Standard_ShortReal LineWidthScale() const { return myLineWidthScale; }
 
   //! Set resolution ratio.
   //! Note that this method rounds @theRatio to nearest integer.
   void SetResolution (unsigned int theResolution,
                       Standard_ShortReal theRatio,
                       Standard_ShortReal theScale)
   {
     myResolution      = (unsigned int )(theScale * theResolution + 0.5f);
     myRenderScale     = theScale;
     myRenderScaleInv  = 1.0f / theScale;
     SetResolutionRatio (theRatio * theScale);
   }
 
   //! Set resolution ratio.
   //! Note that this method rounds @theRatio to nearest integer.
   void SetResolutionRatio (const Standard_ShortReal theRatio)
   {
     myResolutionRatio = theRatio;
     myLineWidthScale  = Max (1.0f, std::floor (theRatio + 0.5f));
   }
 
   //! Return line feater width in pixels.
   Standard_ShortReal LineFeather() const { return myLineFeather; }
 
   //! Set line feater width.
   void SetLineFeather(Standard_ShortReal theValue) { myLineFeather = theValue; }
 
   //! Wrapper over glGetBufferSubData(), implemented as:
   //! - OpenGL 1.5+ (desktop) via glGetBufferSubData();
   //! - OpenGL ES 3.0+ via glMapBufferRange();
   //! - WebGL 2.0+ via gl.getBufferSubData().
   //! @param[in]  theTarget target buffer to map {GLenum}
   //! @param[in]  theOffset offset to the beginning of sub-data {GLintptr}
   //! @param[in]  theSize   number of bytes to read {GLsizeiptr}
   //! @param[out] theData   destination pointer to fill
   //! @return FALSE if functionality is unavailable
   Standard_EXPORT bool GetBufferSubData (unsigned int theTarget, intptr_t theOffset, intptr_t theSize, void* theData);
 
   //! Return Graphics Driver's vendor.
   const TCollection_AsciiString& Vendor() const { return myVendor; }
 
   //! Dumps the content of me into the stream
   Standard_EXPORT void DumpJson (Standard_OStream& theOStream, Standard_Integer theDepth = -1) const;
     
   //! Dumps the content of openGL state into the stream
   Standard_EXPORT void DumpJsonOpenGlState (Standard_OStream& theOStream, Standard_Integer theDepth = -1);
 
   //! Set GL_SHADE_MODEL value.
   Standard_EXPORT void SetShadeModel (Graphic3d_TypeOfShadingModel theModel);
 
 private:
 
   //! Wrapper to system function to retrieve GL function pointer by name.
   Standard_EXPORT void* findProc (const char* theFuncName);
 
   //! Print error if not all functions have been exported by context for reported version.
   //! Note that this will never happen when using GLX, since returned functions can not be validated.
   //! @param theGlVerMajor the OpenGL major version with missing functions
   //! @param theGlVerMinor the OpenGL minor version with missing functions
   //! @param theLastFailedProc function name which cannot be found
   Standard_EXPORT void checkWrongVersion (Standard_Integer theGlVerMajor, Standard_Integer theGlVerMinor,
                                           const char* theLastFailedProc);
 
   //! Private initialization function that should be called only once.
   Standard_EXPORT void init (const Standard_Boolean theIsCoreProfile);
 
 public: //! @name core profiles
 
   OpenGl_GlCore11*     core11ffp;  //!< OpenGL 1.1 core functionality
   OpenGl_GlCore11Fwd*  core11fwd;  //!< OpenGL 1.1 without deprecated entry points
   OpenGl_GlCore15*     core15;     //!< OpenGL 1.5 without deprecated entry points
   OpenGl_GlCore20*     core20;     //!< OpenGL 2.0 without deprecated entry points
   OpenGl_GlCore30*     core30;     //!< OpenGL 3.0 without deprecated entry points
   OpenGl_GlCore32*     core32;     //!< OpenGL 3.2 core profile
   OpenGl_GlCore33*     core33;     //!< OpenGL 3.3 core profile
   OpenGl_GlCore41*     core41;     //!< OpenGL 4.1 core profile
   OpenGl_GlCore42*     core42;     //!< OpenGL 4.2 core profile
   OpenGl_GlCore43*     core43;     //!< OpenGL 4.3 core profile
   OpenGl_GlCore44*     core44;     //!< OpenGL 4.4 core profile
   OpenGl_GlCore45*     core45;     //!< OpenGL 4.5 core profile
   OpenGl_GlCore46*     core46;     //!< OpenGL 4.6 core profile
 
   OpenGl_GlCore15*     core15fwd;  //!< obsolete entry left for code portability; core15 should be used instead
   OpenGl_GlCore20*     core20fwd;  //!< obsolete entry left for code portability; core20 should be used instead
 
   Handle(OpenGl_Caps) caps; //!< context options
 
 public: //! @name extensions
 
   Standard_Boolean       hasGetBufferData;   //!< flag indicating if GetBufferSubData() is supported
   Standard_Boolean       hasPackRowLength;   //!< supporting of GL_PACK_ROW_LENGTH   parameters (any desktop OpenGL; OpenGL ES 3.0)
   Standard_Boolean       hasUnpackRowLength; //!< supporting of GL_UNPACK_ROW_LENGTH parameters (any desktop OpenGL; OpenGL ES 3.0)
   Standard_Boolean       hasHighp;           //!< highp in GLSL ES fragment shader is supported
   Standard_Boolean       hasUintIndex;       //!< GLuint for index buffer is supported (always available on desktop; on OpenGL ES - since 3.0 or as extension GL_OES_element_index_uint)
   Standard_Boolean       hasTexRGBA8;        //!< always available on desktop; on OpenGL ES - since 3.0 or as extension GL_OES_rgb8_rgba8
   Standard_Boolean       hasTexFloatLinear;  //!< texture-filterable state for 32-bit floating texture formats (always on desktop, GL_OES_texture_float_linear within OpenGL ES)
   Standard_Boolean       hasTexSRGB;         //!< sRGB texture    formats (desktop OpenGL 2.1, OpenGL ES 3.0 or OpenGL ES 2.0 + GL_EXT_sRGB)
   Standard_Boolean       hasFboSRGB;         //!< sRGB FBO render targets (desktop OpenGL 2.1, OpenGL ES 3.0)
   Standard_Boolean       hasSRGBControl;     //!< sRGB write control (any desktop OpenGL, OpenGL ES + GL_EXT_sRGB_write_control extension)
   Standard_Boolean       hasFboRenderMipmap; //!< FBO render target could be non-zero mipmap level of texture
   OpenGl_FeatureFlag     hasFlatShading;     //!< Complex flag indicating support of Flat shading (Graphic3d_TypeOfShadingModel_Phong) (always available on desktop; on OpenGL ES - since 3.0 or as extension GL_OES_standard_derivatives)
   OpenGl_FeatureFlag     hasGlslBitwiseOps;  //!< GLSL supports bitwise operations; OpenGL 3.0 / OpenGL ES 3.0 (GLSL 130 / GLSL ES 300) or OpenGL 2.1 + GL_EXT_gpu_shader4
   OpenGl_FeatureFlag     hasDrawBuffers;     //!< Complex flag indicating support of multiple draw buffers (desktop OpenGL 2.0, OpenGL ES 3.0, GL_ARB_draw_buffers, GL_EXT_draw_buffers)
   OpenGl_FeatureFlag     hasFloatBuffer;     //!< Complex flag indicating support of float color buffer format (desktop OpenGL 3.0, GL_ARB_color_buffer_float, GL_EXT_color_buffer_float)
   OpenGl_FeatureFlag     hasHalfFloatBuffer; //!< Complex flag indicating support of half-float color buffer format (desktop OpenGL 3.0, GL_ARB_color_buffer_float, GL_EXT_color_buffer_half_float)
   OpenGl_FeatureFlag     hasSampleVariables; //!< Complex flag indicating support of MSAA variables in GLSL shader (desktop OpenGL 4.0, GL_ARB_sample_shading)
   OpenGl_FeatureFlag     hasGeometryStage;   //!< Complex flag indicating support of Geometry shader (desktop OpenGL 3.2, OpenGL ES 3.2, GL_EXT_geometry_shader)
   Standard_Boolean       arbDrawBuffers;     //!< GL_ARB_draw_buffers
   Standard_Boolean       arbNPTW;            //!< GL_ARB_texture_non_power_of_two
   Standard_Boolean       arbTexRG;           //!< GL_ARB_texture_rg
   Standard_Boolean       arbTexFloat;        //!< GL_ARB_texture_float (on desktop OpenGL - since 3.0 or as extension GL_ARB_texture_float; on OpenGL ES - since 3.0); @sa hasTexFloatLinear for linear filtering support
   OpenGl_ArbSamplerObject* arbSamplerObject; //!< GL_ARB_sampler_objects (on desktop OpenGL - since 3.3 or as extension GL_ARB_sampler_objects; on OpenGL ES - since 3.0)
   OpenGl_ArbTexBindless* arbTexBindless;     //!< GL_ARB_bindless_texture
   OpenGl_ArbTBO*         arbTBO;             //!< GL_ARB_texture_buffer_object (on desktop OpenGL - since 3.1 or as extension GL_ARB_texture_buffer_object; on OpenGL ES - since 3.2)
   Standard_Boolean       arbTboRGB32;        //!< GL_ARB_texture_buffer_object_rgb32 (3-component TBO), in core since 4.0 (on OpenGL ES - since 3.2)
   Standard_Boolean       arbClipControl;     //!< GL_ARB_clip_control, in core since 4.5
   OpenGl_ArbIns*         arbIns;             //!< GL_ARB_draw_instanced (on desktop OpenGL - since 3.1 or as extension GL_ARB_draw_instanced; on OpenGL ES - since 3.0 or as extension GL_ANGLE_instanced_arrays to WebGL 1.0)
   OpenGl_ArbDbg*         arbDbg;             //!< GL_ARB_debug_output (on desktop OpenGL - since 4.3 or as extension GL_ARB_debug_output; on OpenGL ES - since 3.2 or as extension GL_KHR_debug)
   OpenGl_ArbFBO*         arbFBO;             //!< GL_ARB_framebuffer_object
   OpenGl_ArbFBOBlit*     arbFBOBlit;         //!< glBlitFramebuffer function, moved out from OpenGl_ArbFBO structure for compatibility with OpenGL ES 2.0
   Standard_Boolean       arbSampleShading;   //!< GL_ARB_sample_shading
   Standard_Boolean       arbDepthClamp;      //!< GL_ARB_depth_clamp (on desktop OpenGL - since 3.2 or as extensions GL_ARB_depth_clamp,NV_depth_clamp; unavailable on OpenGL ES)
   Standard_Boolean       extFragDepth;       //!< GL_EXT_frag_depth on OpenGL ES 2.0 (gl_FragDepthEXT built-in variable, before OpenGL ES 3.0)
   Standard_Boolean       extDrawBuffers;     //!< GL_EXT_draw_buffers
   OpenGl_ExtGS*          extGS;              //!< GL_EXT_geometry_shader4
   Standard_Boolean       extBgra;            //!< GL_EXT_bgra or GL_EXT_texture_format_BGRA8888 on OpenGL ES
   Standard_Boolean       extTexR16;          //!< GL_EXT_texture_norm16 on OpenGL ES; always available on desktop
   Standard_Boolean       extAnis;            //!< GL_EXT_texture_filter_anisotropic
   Standard_Boolean       extPDS;             //!< GL_EXT_packed_depth_stencil
   Standard_Boolean       atiMem;             //!< GL_ATI_meminfo
   Standard_Boolean       nvxMem;             //!< GL_NVX_gpu_memory_info
   Standard_Boolean       oesSampleVariables; //!< GL_OES_sample_variables
   Standard_Boolean       oesStdDerivatives;  //!< GL_OES_standard_derivatives
 
 public: //! @name public properties tracking current state
 
   OpenGl_MatrixState<Standard_ShortReal> ModelWorldState; //!< state of orientation matrix
   OpenGl_MatrixState<Standard_ShortReal> WorldViewState;  //!< state of orientation matrix
   OpenGl_MatrixState<Standard_ShortReal> ProjectionState; //!< state of projection  matrix
 
 private: // system-dependent fields
 
   Aspect_Drawable         myWindow;   //!< surface           EGLSurface | HWND  | GLXDrawable
   Aspect_Display          myDisplay;  //!< display           EGLDisplay | HDC   | Display*
   Aspect_RenderingContext myGContext; //!< rendering context EGLContext | HGLRC | GLXContext | EAGLContext* | NSOpenGLContext*
 
 private: // context info
 
   typedef NCollection_Shared< NCollection_DataMap<TCollection_AsciiString, Standard_Integer> > OpenGl_DelayReleaseMap;
   typedef NCollection_Shared< NCollection_List<Handle(OpenGl_Resource)> > OpenGl_ResourcesStack;
 
   Handle(OpenGl_ResourcesMap)    mySharedResources; //!< shared resources with unique identification key
   Handle(OpenGl_DelayReleaseMap) myDelayed;         //!< shared resources for delayed release
   Handle(OpenGl_ResourcesStack)  myUnusedResources; //!< stack of resources for delayed clean up
 
   OpenGl_Clipping myClippingState; //!< state of clip planes
 
   void*            myGlLibHandle;          //!< optional handle to GL library
   std::unique_ptr<OpenGl_GlFunctions>
                    myFuncs;                //!< mega structure for all GL functions
   Aspect_GraphicsLibrary myGapi;           //!< GAPI name
   Handle(Image_SupportedFormats)
                    mySupportedFormats;     //!< map of supported texture formats
   Standard_Integer myAnisoMax;             //!< maximum level of anisotropy texture filter
   Standard_Integer myTexClamp;             //!< either GL_CLAMP_TO_EDGE (1.2+) or GL_CLAMP (1.1)
   Standard_Integer myMaxTexDim;            //!< value for GL_MAX_TEXTURE_SIZE
   Standard_Integer myMaxTexCombined;       //!< value for GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS
   Standard_Integer myMaxTexUnitsFFP;       //!< value for GL_MAX_TEXTURE_UNITS (fixed-function pipeline only)
   Standard_Integer myMaxDumpSizeX;         //!< maximum FBO width  for image dump
   Standard_Integer myMaxDumpSizeY;         //!< maximum FBO height for image dump
   Standard_Integer myMaxClipPlanes;        //!< value for GL_MAX_CLIP_PLANES
   Standard_Integer myMaxMsaaSamples;       //!< value for GL_MAX_SAMPLES
   Standard_Integer myMaxDrawBuffers;       //!< value for GL_MAX_DRAW_BUFFERS
   Standard_Integer myMaxColorAttachments;  //!< value for GL_MAX_COLOR_ATTACHMENTS
   Standard_Integer myGlVerMajor;           //!< cached GL version major number
   Standard_Integer myGlVerMinor;           //!< cached GL version minor number
   Standard_Boolean myIsInitialized;        //!< flag indicates initialization state
   Standard_Boolean myIsStereoBuffers;      //!< context supports stereo buffering
   Standard_Boolean myHasMsaaTextures;      //!< context supports MSAA textures
   Standard_Boolean myIsGlNormalizeEnabled; //!< GL_NORMALIZE flag
                                            //!< Used to tell OpenGl that normals should be normalized
   Graphic3d_TextureUnit mySpriteTexUnit;   //!< sampler2D occSamplerPointSprite, texture unit for point sprite texture
 
   Standard_Boolean myHasRayTracing;                 //! indicates whether ray tracing mode is supported
   Standard_Boolean myHasRayTracingTextures;         //! indicates whether textures in ray tracing mode are supported
   Standard_Boolean myHasRayTracingAdaptiveSampling; //! indicates whether adaptive screen sampling in ray tracing mode is supported
   Standard_Boolean myHasRayTracingAdaptiveSamplingAtomic; //! indicates whether atomic adaptive screen sampling in ray tracing mode is supported
 
   Standard_Boolean myHasPBR;                      //!< indicates whether PBR shading model is supported
   Graphic3d_TextureUnit myPBREnvLUTTexUnit;       //!< sampler2D occEnvLUT, texture unit where environment lookup table is expected to be binded (0 if PBR is not supported)
   Graphic3d_TextureUnit myPBRDiffIBLMapSHTexUnit; //!< sampler2D occDiffIBLMapSHCoeffs, texture unit where diffuse (irradiance) IBL map's spherical harmonics coefficients is expected to  be binded
                                                   //!  (0 if PBR is not supported)
   Graphic3d_TextureUnit myPBRSpecIBLMapTexUnit;   //!< samplerCube occSpecIBLMap, texture unit where specular IBL map is expected to  be binded (0 if PBR is not supported)
   Graphic3d_TextureUnit myShadowMapTexUnit;       //!< sampler2D occShadowMapSampler
 
   Graphic3d_TextureUnit myDepthPeelingDepthTexUnit;      //!< sampler2D occDepthPeelingDepth, texture unit for Depth Peeling lookups
   Graphic3d_TextureUnit myDepthPeelingFrontColorTexUnit; //!< sampler2D occDepthPeelingFrontColor, texture unit for Depth Peeling lookups
 
   Handle(OpenGl_ShaderManager) myShaderManager; //! support object for managing shader programs
 
 private: //! @name fields tracking current state
 
   Handle(Graphic3d_Camera)      myCamera;          //!< active camera object
   Handle(OpenGl_FrameStats)     myFrameStats;      //!< structure accumulating frame statistics
   Handle(OpenGl_ShaderProgram)  myActiveProgram;   //!< currently active GLSL program
   Handle(OpenGl_TextureSet)     myActiveTextures;  //!< currently bound textures
                                                    //!< currently active sampler objects
   Standard_Integer              myActiveMockTextures; //!< currently active mock sampler objects
   Handle(OpenGl_FrameBuffer)    myDefaultFbo;      //!< default Frame Buffer Object
   Handle(OpenGl_LineAttributes) myHatchStyles;     //!< resource holding predefined hatch styles patterns
   Standard_Integer              myActiveHatchType; //!< currently activated type of polygon hatch
   Standard_Boolean              myHatchIsEnabled;  //!< current enabled state of polygon hatching rasterization
   Handle(OpenGl_Texture)        myTextureRgbaBlack;//!< mock black texture returning (0, 0, 0, 0)
   Handle(OpenGl_Texture)        myTextureRgbaWhite;//!< mock white texture returning (1, 1, 1, 1)
   Standard_Integer              myViewport[4];     //!< current viewport
   Standard_Integer              myViewportVirt[4]; //!< virtual viewport
   Standard_Integer              myPointSpriteOrig; //!< GL_POINT_SPRITE_COORD_ORIGIN state (GL_UPPER_LEFT by default)
   Standard_Integer              myRenderMode;      //!< value for active rendering mode
   Standard_Integer              myShadeModel;      //!< currently used shade model (glShadeModel)
   Standard_Integer              myPolygonMode;     //!< currently used polygon rasterization mode (glPolygonMode)
   Graphic3d_PolygonOffset       myPolygonOffset;   //!< currently applied polygon offset
   Graphic3d_TypeOfBackfacingModel myFaceCulling;   //!< back face culling mode enabled state (glIsEnabled (GL_CULL_FACE))
   Standard_Integer              myReadBuffer;      //!< current read buffer
   NCollection_Array1<Standard_Integer>
                                 myDrawBuffers;     //!< current draw buffers
   unsigned int                  myDefaultVao;      //!< default Vertex Array Object
   NCollection_Vec4<bool>        myColorMask;       //!< flag indicating writing into color buffer is enabled or disabled (glColorMask)
   Standard_Boolean              myAllowAlphaToCov; //!< flag allowing   GL_SAMPLE_ALPHA_TO_COVERAGE usage
   Standard_Boolean              myAlphaToCoverage; //!< flag indicating GL_SAMPLE_ALPHA_TO_COVERAGE state
   Standard_Boolean              myIsGlDebugCtx;    //!< debug context initialization state
   Standard_Boolean              myIsWindowDeepColor; //!< indicates that window buffer is has deep color pixel format
   Standard_Boolean              myIsSRgbWindow;    //!< indicates that window buffer is sRGB-ready
   Standard_Boolean              myIsSRgbActive;    //!< flag indicating GL_FRAMEBUFFER_SRGB state
   TCollection_AsciiString       myVendor;          //!< Graphics Driver's vendor
   TColStd_PackedMapOfInteger    myFilters[6];      //!< messages suppressing filter (for sources from GL_DEBUG_SOURCE_API_ARB to GL_DEBUG_SOURCE_OTHER_ARB)
   unsigned int                  myResolution;      //!< Pixels density (PPI), defines scaling factor for parameters like text size
   Standard_ShortReal            myResolutionRatio; //!< scaling factor for parameters like text size
                                                    //!  to be properly displayed on device (screen / printer)
   Standard_ShortReal            myLineWidthScale;  //!< scaling factor for line width
   Standard_ShortReal            myLineFeather;     //!< line feater width in pixels
   Standard_ShortReal            myRenderScale;     //!< scaling factor for rendering resolution
   Standard_ShortReal            myRenderScaleInv;  //!< scaling factor for rendering resolution (inverted value)
   OpenGl_Material               myMaterial;        //!< current front/back material state (cached to reduce GL context updates)
 
 private:
 
   //! Copying allowed only within Handles
   OpenGl_Context            (const OpenGl_Context& );
   OpenGl_Context& operator= (const OpenGl_Context& );
 
 };
 
 #endif // _OpenGl_Context_H__

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