Using "viewport" texture in shaders does not work for multisample levels > 1

[cosator]

Steps to reproduce:

• Change multisample level to 1 in Sample.inl
• Build Water Sample and run it
• Notice that Water refraction shows black, instead of bottom texture

Notes:

• Verified on DX11 build on NVIDIA and Intel chipsets.
• Introduced by commit 46793bb "Match multisample mode of the substitute rendertarget & screen buffers with the final destination".
• Changing View.cpp line "int multiSample = renderTarget_ ? renderTarget_->GetMultiSample() : graphics_->GetMultiSample();" to "int multiSample = renderTarget_ ? renderTarget_->GetMultiSample() : 1;" appears to fix the issue.

[cadaver]

This seems to be an oversight in Graphics::ResolveToTexture(Texture2D* destination, const IntRect& viewport) .. basically, resolving backbuffer to a texture.

If the texture is multisampled and has autoresolve on, it should be marked "resolve dirty" so that it will be resolved to non-MS the next time before being sampled by a shader.

The following code needs to be inserted into the function (all API versions) to fix. Oddly, OpenGL appeared to work for me without.

    if (destination->GetMultiSample() > 1 && destination->GetAutoResolve())
        destination->SetResolveDirty(true);

[cosator]

@cadaver I tried the fix that you suggested and it did not work. I tried adding the line both at function entry point and exit point, and it didn't make a difference. I only tried for DX11 on an Intel chipset.

[cadaver]

You're right. It does work on D3D9, but on D3D11 there's something further missing, probably the backbuffer is not being copied right to a multisampled texture. In which case your fix is OK too, and likely better for performance.

[cosator]

My fix was not based on knowledge of what needs to be done, but rather on reverting the change for that particular case. Right now I don't know enough about that portion of code to come up with a robust fix, but this temporary solution seems to work OK for my application until a proper fix is developed.
Thank you so much for looking into it!

[cadaver]

I suspect this may have worked with older drivers (because a black screen in the post-process sample should have been noticeable); however on OpenGL it seems to have always worked, ie. the multisample contents seem to be transported almost "magically" to the texture being sampled. Will submit a PR which essentially reverts the change.