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DirectXTex/DirectXTex.h

@@ -483,6 +483,9 @@ namespace DirectX
         TEX_PMALPHA_IGNORE_SRGB     = 0x1,
             // ignores sRGB colorspace conversions
 
+        TEX_PMALPHA_REVERSE         = 0x2,
+            // converts from premultiplied alpha back to straight alpha
+
         TEX_PMALPHA_SRGB_IN         = 0x1000000,
         TEX_PMALPHA_SRGB_OUT        = 0x2000000,
         TEX_PMALPHA_SRGB            = ( TEX_PMALPHA_SRGB_IN | TEX_PMALPHA_SRGB_OUT ),
@@ -490,9 +493,9 @@ namespace DirectX
             // if the output format type is IsSRGB(), then SRGB_OUT is on by default
     };
 
-    HRESULT __cdecl PremultiplyAlpha( _In_ const Image& srcImage, _In_ DWORD flags, _Out_ ScratchImage& image, bool reverse = false );
+    HRESULT __cdecl PremultiplyAlpha( _In_ const Image& srcImage, _In_ DWORD flags, _Out_ ScratchImage& image );
     HRESULT __cdecl PremultiplyAlpha( _In_reads_(nimages) const Image* srcImages, _In_ size_t nimages, _In_ const TexMetadata& metadata,
-                                      _In_ DWORD flags, _Out_ ScratchImage& result, bool reverse = false);
+                                      _In_ DWORD flags, _Out_ ScratchImage& result );
         // Converts to/from a premultiplied alpha version of the texture
 
     enum TEX_COMPRESS_FLAGS

DirectXTex/DirectXTexPMAlpha.cpp

@@ -198,8 +198,7 @@ _Use_decl_annotations_
 HRESULT DirectX::PremultiplyAlpha(
     const Image& srcImage,
     DWORD flags,
-    ScratchImage& image,
-    bool reverse)
+    ScratchImage& image)
 {
     if (!srcImage.pixels)
         return E_POINTER;
@@ -225,7 +224,7 @@ HRESULT DirectX::PremultiplyAlpha(
         return E_POINTER;
     }
 
-    if (reverse)
+    if (flags & TEX_PMALPHA_REVERSE)
     {
         hr = (flags & TEX_PMALPHA_IGNORE_SRGB) ? DemultiplyAlpha(srcImage, *rimage) : DemultiplyAlphaLinear(srcImage, flags, *rimage);
     }
@@ -252,8 +251,7 @@ HRESULT DirectX::PremultiplyAlpha(
     size_t nimages,
     const TexMetadata& metadata,
     DWORD flags,
-    ScratchImage& result,
-    bool reverse)
+    ScratchImage& result)
 {
     if (!srcImages || !nimages)
         return E_INVALIDARG;
@@ -268,11 +266,11 @@ HRESULT DirectX::PremultiplyAlpha(
     if ((metadata.width > UINT32_MAX) || (metadata.height > UINT32_MAX))
         return E_INVALIDARG;
 
-    if (metadata.IsPMAlpha() != reverse)
+    if (metadata.IsPMAlpha() != ((flags & TEX_PMALPHA_REVERSE) != 0))
         return E_FAIL;
 
     TexMetadata mdata2 = metadata;
-    mdata2.SetAlphaMode(reverse ? TEX_ALPHA_MODE_STRAIGHT : TEX_ALPHA_MODE_PREMULTIPLIED);
+    mdata2.SetAlphaMode((flags & TEX_PMALPHA_REVERSE) ? TEX_ALPHA_MODE_STRAIGHT : TEX_ALPHA_MODE_PREMULTIPLIED);
     HRESULT hr = result.Initialize(mdata2);
     if (FAILED(hr))
         return hr;
@@ -311,7 +309,7 @@ HRESULT DirectX::PremultiplyAlpha(
             return E_FAIL;
         }
 
-        if (reverse)
+        if (flags & TEX_PMALPHA_REVERSE)
         {
             hr = (flags & TEX_PMALPHA_IGNORE_SRGB) ? DemultiplyAlpha(src, dst) : DemultiplyAlphaLinear(src, flags, dst);
         }

Texconv/texconv.cpp

@@ -1557,7 +1557,7 @@ int __cdecl wmain(_In_ int argc, _In_z_count_(argc) wchar_t* argv[])
                     return 1;
                 }
 
-                hr = PremultiplyAlpha(img, nimg, info, dwSRGB, *timage, true);
+                hr = PremultiplyAlpha(img, nimg, info, TEX_PMALPHA_REVERSE | dwSRGB, *timage);
                 if (FAILED(hr))
                 {
                     wprintf(L" FAILED [demultiply alpha] (%x)\n", hr);