This is the main way to draw GL content in GTK+. It takes a render buffer ID (source_type == GL_RENDERBUFFER) or a texture id (source_type == GL_TEXTURE) and draws it onto cr with an OVER operation, respecting the current clip. The top left corner of the rectangle specified by x, y, width and height will be drawn at the current (0,0) position of the cairo_t.
This will work for *all* cairo_t, as long as window is realized, but the fallback implementation that reads back the pixels from the buffer may be used in the general case. In the case of direct drawing to a window with no special effects applied to cr it will however use a more efficient approach.
Calling this may change the current GL context.
a cairo context
The window we're rendering for (not necessarily into)
The GL ID of the source buffer
The type of the source
The scale-factor that the source buffer is allocated for
The source x position in source to start copying from in GL coordinates
The source y position in source to start copying from in GL coordinates
The width of the region to draw
The height of the region to draw