overlay support in windows/opengl environment

Question

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?

Answer 1

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.