In Blender 2.90 EEVEE materials were refactored that introduced crashes on Intel
GPUs on Windows. The crash happened in the `local_context_workaround` that temporary
stored compiled materials in a binary form to reload it in the main GL context.
It has been tested that the workaround isn't needed anymore for HD6xx GPUs, but it
is still needed for HD4000.
After several unsuccesfull fixes we came to the conclusion that we could not support
the local context workaround and needed to come with a different workaround. The idea
of this patch is that in these cases there is only a single context that is used for
rendering. Threads that uses these contextes are guarded by a mutex and will block.
Impact on User Level:
* Due to main mutex lock the UI freezes when rendering or baking or feel less snappy
Reviewed By: Clément Foucault, Brecht van Lommel
Differential Revision: https://developer.blender.org/D8410
Previously, we had one global `GPU_matrix` stack, so the API was not
thread safe. This patch makes the stack be per `GPUContext`, effectively
making it local per thread (`GPUContext` is located in thread local
storage).
Reviewed By: brecht
Differential Revision: https://developer.blender.org/D5405
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instead of being ThreadLocal and leading to incorrect usage.
We still enforce no framebuffer when changing context. We can lift this
restriction later.
GPUFrameBuffers were being free when no context was attached or in the
wrong gl context. This make sure this does not happen again.
You can now safely free any gl resource from any thread (well as long as
it's not used anymore!).
