Help - 2 Viewports, 1 regular, 1 zoomed, incremental changes but long draw times.

Just to make sure I understand something. If I create two windows via Viewports and double buffering is enabled, I will have to redraw each viewport each frame? If so, does it mean that swapbuffers clears out the back buffer each time it is called, hence previous images can’t be reused?

If this is true, what if I have an image where only a small section of it changes at a time? I was hoping to just change that section (no depth buffer being used) instead of redrawing the image. The section is random, so it makes a mess of display lists. Also the entire image takes long to display (9 secs) since I don’t have an OpenGL compliant card (I am hoping to make the program useable on PC’s without OpenGL acceleration). The section that changes is typically less than 10 tri’s which draws in no time. I’ve heard about auxillary buffers so theoretically I can update an auxillary buffer that won’t get redrawn then blit the image to the back buffer. However I understand that not all PCs support an auxillary buffer so it might not work on some.

What’s the best thing to do then?

Hi !

Mesa have (or at least had) support for redrawing a part of the framebuffer, at least I think so, I am not sure if this is still available though, if you don’t use hardware OpenGL you might consider using that, that would also give you OpenGL 1.3 for free.