Typed Buffers SRV Not Working

[tengel-lux]

I ran into an issue using e.g., Buffer<float2>. In which case the format would be DXGI_FORMAT_R32G32_FLOAT and StructureByteStride should be set to 0.
https://learn.microsoft.com/en-us/windows/win32/api/d3d12/ns-d3d12-d3d12_buffer_srv

[maoliver-amd]

For clarification gfx only allows creating buffers on the host using a known host type which works fine when accessing using StructuredBuffer in HLSL. However, if it is desired to use a HLSL Buffer with automatic conversion from the internal memory type then this requires creating the host buffer with types beyond what are known to the host.
The example here being the ability to create a DXGI_FORMAT_R8G8_SNORM buffer on the host and then access it in shader code as a Buffer<float2> and get automatic snorm to float conversion

[gboisse]

We could add a format field to the GfxBuffer type (like we have stride atm), make it default to say DXGI_FORMAT_UNKNOWN (which is 0 conveniently so there's nothing to do there 🙂) and add corresponding getters and setters.

But I'd imagine we'd also need to know how the resource is used at shader level...
Cause you can bind a buffer resource either as StructuredBuffer<> or Buffer<> or even change binding type between passes, do we know if we can get this information from DXC's reflection data?

[tengel-lux]

I've open the ticket because I ran into this issue and took me some time to realize what was going on. It's not a must-have feature imo, but it could be made to warn/error when using it to prevent possibly silent issues then. Up to you to decide if we should support it or not.

To my understanding we'd need to create an SRV with specific format, so API user would need to pass it:

• On buffer creation, as mentioned above, or
• gfxProgramSetParameter<GfxBuffer> have an extra DXGI_FORMAT parameter

The D3D12_SHADER_INPUT_BIND_DESC for Buffer<float2> looks like this (I couldn't find a spec on this so tested locally):

added this texture_buffer_ flag to createRootSignature and filled it

case D3D_SRV_DIMENSION_BUFFER:
	kernel_parameter.type_ = Kernel::Parameter::kType_Buffer;
	kernel_parameter.texture_buffer_ = resource_desc.Type == D3D_SIT_TEXTURE;

and when we create the SRV I check it and create appropriately

if (parameter.texture_buffer_) // typed buffer SRV 
{
	srv_desc.ViewDimension = D3D12_SRV_DIMENSION_BUFFER;
	srv_desc.Shader4ComponentMapping = D3D12_DEFAULT_SHADER_4_COMPONENT_MAPPING;
	srv_desc.Buffer.FirstElement        = gfx_buffer.data_offset_ / 2;
	srv_desc.Buffer.NumElements         = (uint32_t)(buffer.size / 2);
	srv_desc.Format                     = DXGI_FORMAT_R8G8_SNORM;
	srv_desc.Buffer.StructureByteStride = 0;
	srv_desc.Buffer.Flags               = D3D12_BUFFER_SRV_FLAG_NONE;
}
else // structured (same as old code)
{
	srv_desc.ViewDimension              = D3D12_SRV_DIMENSION_BUFFER;
	srv_desc.Shader4ComponentMapping    = D3D12_DEFAULT_SHADER_4_COMPONENT_MAPPING;
	srv_desc.Buffer.FirstElement        = gfx_buffer.data_offset_ / buffer.stride;
	srv_desc.Buffer.NumElements         = (uint32_t)(buffer.size / buffer.stride);
	srv_desc.Buffer.StructureByteStride = buffer.stride;
}

and inspecting the SRV with PIX, so looks ok.

also just realized that raw buffer SRV is also not working (I have a fix here for UAV but SRV were not changed #175)