UCanvasRenderTarget2D crashes on some video cards if the BGRA format is selected

The reason for the crash is that the underlying resource uses DXGI_FORMAT_B8G8R8A8_TYPELESS, and UAV support for that format is optional. UCanvasRenderTarget2D sets bCanCreateUAV to true always, without checking RHIIsTypedUAVLoadSupported() for the format. It does this because it might need to generate mips for the texture, and sometimes this uses a compute shader.

What should happen instead is that we don't request UAV creation if the card can't do UAVs for the format, and mip generation should be forced to use the raster path if there's no UAV. UCanvasRenderTarget2D shouldn't deal with any of this, it should be moved to the base class (UTextureRenderTarget2D) if possible.

Original bug report came from this UDN: [Link Removed]

• Create a Canvas Render Target
• Set format to RTF_RGBA8
• Observe crash:
  Fatal error: Direct3DDevice->CreateUnorderedAccessView failed with error E_INVALIDARG

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The error report came from a machine running Win10 1607 (old!) on an Nvidia GTX 1060. No information about driver version.