Class TGLFeatures

Maximum number of texture units you can safely always use. If EnableFixedFunction, this is MaxTextureUnitsFixedFunction, otherwise MaxTextureUnitsShaders.

OpenGL versions supported. Checked by looking at GL version string and by checking whether actual entry points are available.

This is important because bad OpenGL implementations (like the horrible ATI Linux closed drivers) sometimes lie, claiming support in the GL version string but actually lacking proper function entry points. We check the actual presence of entry points (GLExt.Load_GL_version_x_x do that).

We *also* check version string (TGLVersion.AtLeast), since OpenGL may have some buggy entry point in case of work-in-progress features (not yet advertised in GL version string), e.g. Mesa 6.x had such buggy glStencilOpSeparate. This is correct OpenGL behavior AFAIK, and we handle it.

Is the extension below loaded. Note: we prefer to avoid exposing directly each extension presence like below. Instead most interesting extensions are wrapped in "features" like UseMultiTexturing, see lower.

GL_CLAMP_TO_EDGE, if available in current OpenGL version. Otherwise GL_CLAMP.

Use this (insteaf of direct GL_CLAMP_TO_EDGE) to work with really ancient OpenGL versions before 1.2. Note that our engine officially supports only OpenGL >= 1.2, so don't expect everything to work smootly with such ancient OpenGL anyway!

Constant (for given context) OpenGL limits. Initialized to 0 if appropriate OpenGL functionality is not available.

Note that MaxLights is only relevant if we use OpenGL fixed-function pipeline. Otherwise the actual limit is defined purely by Scene.RenderOptions.MaxLightsPerShape, specific to each TCastleScene, and is completely configurable (can be higher or lower than MaxLights).

Number of texture units available for fixed-function pipeline. Equal to 0 on OpenGLES (that doesn't have fixed-function pipeline). Equal to glGetInteger(GL_MAX_TEXTURE_UNITS), if multi-texturing available. Equal to 1 (OpenGL supports always 1 texture) otherwise.

Number of texture units available for shader pipeline.

Are all OpenGL multi-texturing extensions for VRML/X3D MultiTexture support available.

This used to check a couple of multitexturing extensions, like ARB_multitexture. Right now, it simply checks for OpenGL 1.3 version. It is supported by virtually all existing GPUs. So it's acceptable to just check it, and write your code for 1.3, and eventual fallback code (when this is false) write only for really ancient GPUs.

Are 3D textures supported by OpenGL. If they are, note that GL_TEXTURE_3D and GL_TEXTURE_3D_EXT are equal, so often both Texture3D = gsStandard and Texture3D = gsExtension cases may be handled by the same code.

Is Framebuffer supported. Value gsExtension means that EXT_framebuffer_object is used, gsStandard means that ARB_framebuffer_object (which is a "core extesion", present the same way in OpenGL 3 core, also in OpenGL ES >= 2.0 core) is available.

Is multisampling possible for FBO buffers and textures. Although these are two orthogonal features of OpenGL, in practice you want to use multisample for both FBO buffers and textures, or for none — otherwise, FBO can not be initialized correctly when you mix various multisample settings.

How multi-sampling was initialized for this OpenGL context. Value = 1 means that no multi-sampling is initialized. Values > 1 mean that you have multi-sampling, with given number of samples per pixel. Contrast this with TCastleWindow.MultiSampling or TOpenGLControl.MultiSampling, that say how many samples you wanted to get.

Does OpenGL context have depth buffer packed with stencil buffer. See OpenGL extensions EXT_packed_depth_stencil and OES_packed_depth_stencil (http://www.opengl.org/registry/specs/EXT/packed_depth_stencil.txt, https://www.khronos.org/registry/OpenGL/extensions/OES/OES_packed_depth_stencil.txt) for explanation what does it mean.

This is important for FBOs, as the depth/stencil have to be set up differently depending on PackedDepthStencil value. This is also important for all code using TGLRenderToTexture with TGLRenderToTexture.Buffer equal tbDepth or tbColorAndDepth: your depth texture must be prepared differently, to include both depth+stencil data, to work.

For now, this is simply equal to GL_EXT_packed_depth_stencil. (TODO: for core OpenGL 3, how to detect should we use packed version? http://www.opengl.org/registry/specs/ARB/framebuffer_object.txt incorporates EXT_packed_depth_stencil, so forward-compatible contexts do not need to declare it. Should we assume that forward-compatible gl 3 contexts always have depth/stencil packed?)

Does OpenGL context support shadow volumes. This simply checks do we have stencil buffer with at least 4 bits for now.

Are non-power-of-2 textures supported.

Are cubemaps supported.

gsExtension means GL_ARB_texture_cube_map on core OpenGL. gsStandard means standard feature of OpenGL or OpenGL ES. Since the constants defined by ARB_texture_cube_map were promoted to core with the same values, the distinction between gsExtension and gsStandard in practice doesn't exist.

Which texture compression formats are supported.

VBO support (in OpenGL (ES) core).

glBlendColor and GL_CONSTANT_ALPHA support.

Support for float texture formats for glTexImage2d.

Support for depth texture formats for glTexImage2d.

GLSL shaders support.

Note: Setting it is allowed for now, as a simple way to force non-shader rendering, to test it. You should not use this or rely it will be available in future versions.

Enable OpenGL fixed-function rendering on desktops.

• This makes Gouraud-shaded shapes rendered using OpenGL fixed-function pipeline on desktops.

• It also makes TDrawableImage.Draw, DrawPrimitive2D (and consequently most of the 2D user-interface) rendered using OpenGL fixed-function pipeline on desktops.

• It also allows you to use fixed-function pipeline calls in the TCastleWindow.OnRender callback, TCastleUserInterface.Render override and related places.

• It also allows some deprecated rendering features like WindowPos to continue to work.

This is False by default on modern GPUs (that have good GLSL support).

On OpenGLES, it must be False always, since OpenGLES >= 2 has no fixed-function pipeline.

Total and current memory available. Call Memory.Refresh whenever needed.