scratchFramebuffer

Returns an OpenGL framebuffer object suitable for offscreen drawing. The framebuffer has a 32-bit color buffer and a 32-bit depth buffer, both attached as OpenGL texture 2D objects.
The framebuffer may be used by any drawable and for any purpose. However, the draw context makes no guarantees about the framebuffer's contents. Drawables must clear the framebuffer before use, and must assume its contents may be modified by another drawable, either during the current frame or in a subsequent frame.
The OpenGL framebuffer object is created on first use and cached. Subsequent calls to this method return the cached buffer object.