This retrieves OpenGL function pointers, and will use them in subsequent
operation.
Usually, you can simply call the GL context APIs from this callback (e.g.
glXGetProcAddressARB or wglGetProcAddress), but some APIs do not always
return pointers for all standard functions (even if present); in this
case you have to compensate by looking up these functions yourself when
libmpv wants to resolve them through this callback.
libmpv will not normally attempt to resolve GL functions on its own, nor
does it link to GL libraries directly.
This retrieves OpenGL function pointers, and will use them in subsequent operation. Usually, you can simply call the GL context APIs from this callback (e.g. glXGetProcAddressARB or wglGetProcAddress), but some APIs do not always return pointers for all standard functions (even if present); in this case you have to compensate by looking up these functions yourself when libmpv wants to resolve them through this callback. libmpv will not normally attempt to resolve GL functions on its own, nor does it link to GL libraries directly.