A gdk.glcontext.GLContext is not tied to any particular normal framebuffer.
For instance, it cannot draw to the surface back buffer. The GDK
repaint system is in full control of the painting to that. Instead,
you can create render buffers or textures and use func@cairo_draw_from_gl
in the draw function of your widget to draw them. Then GDK will handle
the integration of your rendering with that of other widgets.
Support for gdk.glcontext.GLContext is platform-specific and context creation
can fail, returning null context.
A gdk.glcontext.GLContext has to be made "current" in order to start using
it, otherwise any OpenGL call will be ignored.
You will need to make the gdk.glcontext.GLContext the current context before issuing
OpenGL calls; the system sends OpenGL commands to whichever context is current.
It is possible to have multiple contexts, so you always need to ensure that
the one which you want to draw with is the current one before issuing commands:
gdk_gl_context_make_current (context);
You can now perform your drawing using OpenGL commands.
gdk.glcontext.GLContext is an object representing a platform-specific OpenGL draw context.
gdk.glcontext.GLContexts are created for a surface using gdk.surface.Surface.createGlContext, and the context will match the characteristics of the surface.
A gdk.glcontext.GLContext is not tied to any particular normal framebuffer. For instance, it cannot draw to the surface back buffer. The GDK repaint system is in full control of the painting to that. Instead, you can create render buffers or textures and use func@cairo_draw_from_gl in the draw function of your widget to draw them. Then GDK will handle the integration of your rendering with that of other widgets.
Support for gdk.glcontext.GLContext is platform-specific and context creation can fail, returning null context.
A gdk.glcontext.GLContext has to be made "current" in order to start using it, otherwise any OpenGL call will be ignored.
Creating a new OpenGL context
In order to create a new gdk.glcontext.GLContext instance you need a gdk.surface.Surface, which you typically get during the realize call of a widget.
A gdk.glcontext.GLContext is not realized until either gdk.glcontext.GLContext.makeCurrent or gdk.glcontext.GLContext.realize is called. It is possible to specify details of the GL context like the OpenGL version to be used, or whether the GL context should have extra state validation enabled after calling gdk.surface.Surface.createGlContext by calling gdk.glcontext.GLContext.realize. If the realization fails you have the option to change the settings of the gdk.glcontext.GLContext and try again.
Using a GdkGLContext
You will need to make the gdk.glcontext.GLContext the current context before issuing OpenGL calls; the system sends OpenGL commands to whichever context is current. It is possible to have multiple contexts, so you always need to ensure that the one which you want to draw with is the current one before issuing commands:
You can now perform your drawing using OpenGL commands.
You can check which gdk.glcontext.GLContext is the current one by using gdk.glcontext.GLContext.getCurrent; you can also unset any gdk.glcontext.GLContext that is currently set by calling gdk.glcontext.GLContext.clearCurrent.