That was a nice and funny hunt, albeit rather time consumming!
To summarize, so far code was using a static global gpu_buffer for pbvh vbo drawing
of 'grid' types (multires mostly?).
There were two issues here:
1) Global gpu buffer was assigned to GPU_PBVH_Buffers->index_buf, but then nearly no
check was done when freeing that buffer, to ensure we were not freeing the global one
(not totally sure this one was actually causing any issue, but was bad and unsafe anyway).
Was solved by adding a flag to GPU_PBVH_Buffers to indicate when we are using some
'common' buffer here, which freeing is handled separately.
2) Main issue: if several multires objects in sculpt mode with different grid size
were present simultaneously, the global gpu buffer had to be resized for each object draw
(i.e., freed and re-allocated), but then the pbvh nodes from other objects storing freed reference
to that global buffer had no way to know that it had been freed, which was causing the segfault & crash.
Was solved by getting rid of that global buffer, and instead allocating one 'grid_commmon_gpu_buffer' per pbvh.
Told ya baby, globals are *PURE EVIL*!
Remove legacy code completely, now dyntopo, multires et al even work on
GL 1.1 for really hardcore users :p
Real purpose here though is to be able to have fast multires drawing
even with VBO off, since it requires using indices for vertex buffers.
Also made own code elf puke an eaten normal update function which
made multires not update normals in solid mode...sorry.
option.
This makes sense, since contexts get created at runtime, there is little
reason to require recompilation for this.
Only works on linux currently, will be doing more OSs later
patch number D706 with changes:
- WITH_GPU_DEBUG just creates a debug context (and enables the debug messaging
system functions) but leaves the checks we had intact. Old patch
added the debug functionality only if we had the flag on to save some
performance.
Rationale here is that we might not want to recompile blender just to get
the extra information, and having users start blender with a -d flag to
get the extra information is also useful for bug reports. Those checks already
existed and most expensive ones are hidden behind a debug mode check
so performance should not be that bad.
- Did some cleanup of existing functionality:
When things go wrong blender side, just print the error,
don't check for GL errors first.
- Did not port changes needed for GLES to regular glew.h
- Got rid of duplicate or very similar new functionality.
Generally, code is more moving things around/cleanup and should work exactly
as before apart from the debug context, so it's safe to add even now.
It also provides a nice substitute function for glu error descriptions
