real hard fbo issue

First off, lets state some the relevant keywords such that a google search has a prayer of finding this...

GL_FRAMEBUFFER_UNSUPPORTED_EXT
glFramebufferTexture2DEXT

OK, so here is the lowdown. It is critically important for most of the really interesting things I want to do to be able to allocate framebuffer objects that render their information to textures.

On the mac, I would create a texture and set it on the framebuffer object and it would work.
On windows, I would always get the above error. Now, pray tell, how would it be possible that textured framebuffers are supported on the mac but not on windows *on the same machine*?

Well, I checked a lot of things. I thought that perhaps this was because one was using pbuffers and the other was using swing's fbo pipleline. I changed the window to be a awt canvas (thus rendering to the native window surface) instead of a swing GLJPanel.

I set up a simple test case using an example from the web (that failed, btw.)

I downloaded lwjgl, setup a test case, and ran an example (that also failed, btw).

I spent hours searching the internet. This is all in my spare time after work, so I get at most 2 hours a day to work on this stuff and that is only a couple times/week. One serious gl problem can set me back several weeks.

I also printed out every single variable I could think of that might affect this operation (pixel store state, pixel transfer state, read/draw buffer status, etc.)

Anyway, to stop holding people in suspense, what was causing the allocation to fail?

It was because I wasn't setting the min and mag filters on the texture before I allocated the FBO.

Min and mag filter specify what the texture lookups should be doing when there are more textels than pixels (minication) and when there are more pixels that textels (magnifying the texture). They are attributes that affect how the texture is *read* from memory, not how it is written.

In any case, in the document for FBO's it explicitly states that mipmapped images are not supported even thought the fbo texture renderbuffer call takes a level.

If you look at the defaults for minfilter and magfilter, they are GL_NEAREST_MIPMAP_LINEAR.

Well, NVIDIA cards are picky about this. Apparently, just setting the min and mag filters makes the texture object a mipmap texture object and the fbo allocate will fail with unsupported (which is true in a pedantic, brittle, poorly thought out sense I guess).

So anyway, a couple evenings of debugging and trying out anything I could think of and the answer is simple. When you want to use a texture on an FBO, set its min and mag filters to either LINEAR, CLAMP, or CLAMP_TO_EDGE. Or probably any constant that doesn't explicitly say mipmap in it...

Jeez what a PITA.