FBO issue: glViewport set, only draws one part
Note: this message is cross-posted in OpenGL coding: Advanced. [B]Please help, it's a stumper
I have only ever been able to get FBOs working when they are 512x512 or display WxH, mainly because other sized FBOs have unpredictable coordinate systems or unpredictably "clipped" results. Using just the two sizes I mentioned, everything has been working just fine until recently I hit another wall:
I am using a variety of FBOs in an application, and I reach a point in the rendering pipeline where FBOs start breaking down, where four particular FBOs end up clipped showing only the lower right quarter (it's not exactly a quarter). Or, it will draw only the bottom half. While it tastes like undefined behavior, it has some predictability to which quadrant, for instance. It's all the same FBO, but there are four operations on this same fbo in succession, and they all seem meshed together, like someone shuffled parts of them.
- I tried solving this with glFinish() added to the end of each of the four successive calls, but this made no difference.
- Someone said "hey, your glViewport must be messed up" but that's not possible because the same code and FBOs are used elsewhere on the screen at the same time with no issue. I used glViewport(0,0,fbo->w,fbo->h), which are 512x512 or screen WxH.
The same rendering code that is between the fbo bind/unbind is used elsewhere without issue.
- Switching the FBOs between various "flavors" (depth, depth stencil, depth color, color) does not affect it.
- Changing the uniqueness does not affect it (using a different FBO id that is used less frequently)...
- Changing FBO size only changes how much is drawn correctly, and in the opposite way you would think (bigger=more clipped).
- Turning off scissor test doesn't fix it.
- Clearing the depth buffer doesn't matter.
- Muffing with "near/far" values makes no difference.