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GL \ Procedures query
OpenGL.Net support various APIs, which function pointers are loaded at run-time. This is performed by calling Gl.BindAPI() method, just after an OpenGL context is made current on the current thread. This method loads the specific OpenGL implementation pointers for the current thread (threads have local storage for every function pointer, hence this function shall be called for each thread). If you use the DeviceContext you don't have to worry about calling Gl.BindAPI() yourself.
OpenGL.Net is aware of function aliases. Indeed there is a chance to execute a core function or an extension functions, depending on the current OpenGL implementation offered by the driver.
However, OpenGL.Net does not declare a method for each entry point available. Instead, make use of the function aliasing to scale the execution of the implementation currently available. Indeed a method can actually point to one of the many (aliasing) functions. For example, consider the following code:
[AliasOf("glGenBuffersARB")]
[RequiredByFeature("GL_VERSION_1_5")]
[RequiredByFeature("GL_VERSION_ES_CM_1_0", Api = "gles1")]
[RequiredByFeature("GL_ES_VERSION_2_0", Api = "gles2")]
[RequiredByFeature("GL_ARB_vertex_buffer_object")]
public static void GenBuffers(UInt32[] buffers) { ... }
It means that glGenBuffers can be aliased by glGenBuffers (core API, including ES variants) or glGenBuffersARB (defined by the GL_ARB_vertex_buffer_object_extension). But, which is the function actually called if multiple entry points are available?
The OpenGL.Net procedure loader prefers the following entry points, in that order:
- Core API functions (OpenGL API or OpenGL ES API)
- ARB extension functions (ARB suffix)
- EXT extension functions (EXT suffix)
- Vendor-specific extension functions (i.e. _NV, _AMD, _INTEL...)
The platform library used for loading OpenGL function pointers depends on the version of the current OpenGL context. The currently supported APIs are:
- OpenGL (up to 4.5)
- OpenGL ES
- OpenGL ES 2+ (up to 3.2)
You can find more precise information about on Platform page.
Indeed, you are aware that you cannot bind your application to the old extension methods. Instead, you need to take into account that the library entry points can execute core API functions. Usually this is not a problem, since strange side-effects due function promotion are very limited.
Every function is checked against errors automatically; in this way is is possible to spot any error as soon it is generated, facilitating the application debugging. However, this feature is available only on debug builds.
In the the user executes a function currently undefined on the running system, the method will throw a NullReferenceException. However, if running with a debug build, an assertion is executed with a descriptive message.