I have to display an image and text overlay, when text overlay contains many strings, but only one changes from frame to frame. I want to avoid redraw of the entire overlay and only update what has changed.
I tried wglCreateLayerContext but my GPU seems to not support it (PIXELFORMATDESCRIPTOR bReserved is 0).
What is the most efficient way to redraw only part of text overlay?
Redrawing the whole framebuffer is the canonical way in OpenGL. You can use Framebuffer Objects (FBO) to create several off-screen drawing surfaces, to which you render the individual layers. Then you composit the layers into a composite image presented on screen.
but only one changes from frame to frame. I want to avoid redraw of the entire overlay
Why? Figuring out what parts need redraw, masking them, do only a partial clear, updating it, etc. takes more time and effort than to simply redraw the whole text overlay.