D3D11: Texture - fix DDS mipmap truncation issue (#3290)

Compressed texture can't have mipmaps beyond size 4x4, so remove the last two (2x2, 1x1). However the caller can have images which does not have the full mipmaps chain or already removed the last two mipmaps. The code unconditionally removed the last mipmaps which can be useful.

Co-authored-by: stupak <[email protected]>

RenderSystems/Direct3D11/src/OgreD3D11Texture.cpp

@@ -244,7 +244,11 @@ namespace Ogre
         // determine total number of mipmaps including main one (d3d11 convention)
         UINT numMips = (mNumMipmaps == MIP_UNLIMITED || (1U << mNumMipmaps) > std::max(mSrcWidth, mSrcHeight)) ? 0 : mNumMipmaps + 1;
         if(D3D11Mappings::_isBinaryCompressedFormat(mD3DFormat) && numMips > 1)
-            numMips = std::max(1U, numMips - 2);
+        {
+            // Compressed texture can't have mipmaps beyond size 4x4, so remove the last two (2x2, 1x1)
+            UINT nMaxMips = getMaxMipmaps() + 1;
+            numMips = std::max(1U, std::min(numMips, nMaxMips - 2));
+        }
 
         D3D11_TEXTURE2D_DESC desc;
         desc.Width          = static_cast<UINT>(mSrcWidth);