One cannot pass NULL to MapSubresource for the parameter D3D11_MAPPED_SUBRESOURCE *pMappedResource

[adiba]

Since MapSubresource returns the mapped subresource rather than taking a destination pointer, there is no way to pass pMappedResource = NULL to Map, which is required for the ReadFromSubresource operation.

Relevant docs:

• https://docs.microsoft.com/en-us/windows/desktop/api/d3d11/nf-d3d11-id3d11devicecontext-map#null-pointers-for-pmappedresource
• https://docs.microsoft.com/en-us/windows/desktop/api/d3d11_3/nf-d3d11_3-id3d11device3-readfromsubresource#remarks

[h1cks]

I've dug through this one and it definitely is a bug and I believe we can fix this without a breaking change. But relies on use of a default parameter to be added.

The base call into MapSubresource is the problem, its calling by mapping a databox address which then always passes a non null address to Map Sub resource.

Need to understand what to set in the mapping xml to pass as a nullable struct. Then test the struct for null in the code, prior to mapping it to a reference. I feel that this will need to be hand coded rather than auto generated. Additional changes up the call tree are required to pass through a flag to make the input variable pass whether the call should be made with a null or a data struct.

Need some advice on how to set up the mapping xml so to hand code the call to MapSubresource

[h1cks]

Update: Still working through the fix, may have to rethink a couple of parts of the proposed solution.