Double buffer issue about rpi-opengl-without-x HOT 2 CLOSED

hi @gitbf

I am not the author of the double buffer mechanism, that credit goes to here: https://github.com/eyelash/tutorials/blob/master/drm-gbm.c

But I understand your problem, I had the same issue when I was working on a similar project. I have two solutions:

• Option A, render everything into an OpenGL framebuffer (or renderbuffer). You can still use double buffering for the final output, but your GUI will be rendered into separate framebuffer/renderbuffer. You will essentially have a single off-screen buffer. Even at full HD resolution, the extra framebuffer should only occupy 6.2MB of GPU memory. You can then have two choices to copy the framebuffer to the screen (to the backbuffer):
  • Via glBlitFramebuffer, but that's only available if you replace EGL_OPENGL_ES2_BIT with EGL_OPENGL_ES3_BIT (glBlitFramebuffer is only available in OpenGL ES 3), but I have not tested it personally.
  • Via a shader program. Simply load the framebuffer attachment (the RGB texture) into a shader program, and render it onto a full-screen quad polygon. I can walk you through it.
• Option B, don't use double buffering at all. You can force single buffering by adding EGL_RENDER_BUFFER, EGL_SINGLE_BUFFER, to the configAttribs on line 142 in triangle_rpi4.c and not using gbmSwapBuffers at all. But I can not guarantee it will work. I was only able to get this (single buffer mode) working on Raspberry Pi 3.

I recommend the framebuffer option.

edit: Should have been: "replace EGL_OPENGL_ES2_BIT with EGL_OPENGL_ES3_BIT", not the other way around.

from rpi-opengl-without-x.

Thanks, I'll give it a try.

from rpi-opengl-without-x.