D3D12: Unhandled exception when creating more than 64 samplers

[falia18]

Describe the bug
On D3D12, creating more than 64 samplers will throw an exception in DescriptorAllocatorD3D12::alloc() on line device->CreateSampler(&sd, cpuHandle);

To Reproduce
Steps to reproduce the behavior:

1. Create at least 65 different texture samplers
2. Launch with D3D12 renderer
3. See error

I've forked and edited example 6-bump to reproduce the issue (https://github.com/falia18/bgfx/tree/d3d12-sampler-crash-example)
Clone the project and switch to branch d3d12-sampler-crash-example
Launch example 6-bump with --d3d12 and crash will occur after ~20 frames.

Expected behavior
Sampler creation proceeds without exception.

Additional context
Tested on Windows 10 with both NVIDIA and AMD GPU

[bkaradzic]

Did you test it in debug build?

[falia18]

Release and debug, both crash

[falia18]

I've had time to look a bit through the code and I suspect the problem comes from the fact that m_numDescriptorsPerBlock (in m_samplerAllocator.create() ) is initialized with BGFX_CONFIG_MAX_TEXTURE_SAMPLERS in RendererContextD3D12::init().
Not sure what 'm_numDescriptorsPerBlock` is supposed to do but if initialized at 1 it seems to work as intended.

[bkaradzic]

falia18@ef42e58

[bkaradzic]

@falia18 this is partial fix... I'm still working on proper fix.