convert internal bitmap formats transparency->alpha

Image formats and graphics APIs use alpha, not transparency,
so change our internal formats and data structures to work directly
with alpha, so we don't need to modify data before we push it to
graphics APIs.

Change-Id: I537f77f79e83876be11d787901df42710d190842
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/108919
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

8 files changed, 17 insertions, 15 deletions

diff --git a/vcl/inc/bitmap/ScanlineTools.hxx b/vcl/inc/bitmap/ScanlineTools.hxx
index c343cf34f61e..98e702549f2b 100644
--- a/vcl/inc/bitmap/ScanlineTools.hxx
+++ b/vcl/inc/bitmap/ScanlineTools.hxx
@@ -46,7 +46,7 @@ public:
 
     virtual void writePixel(Color nColor) override
     {
-        *pData++ = 255 - nColor.GetAlpha();
+        *pData++ = nColor.GetAlpha();
         *pData++ = nColor.GetRed();
         *pData++ = nColor.GetGreen();
         *pData++ = nColor.GetBlue();
diff --git a/vcl/qa/cppunit/ScanlineToolsTest.cxx b/vcl/qa/cppunit/ScanlineToolsTest.cxx
index c6751b827ca1..3a4fc7da9348 100644
--- a/vcl/qa/cppunit/ScanlineToolsTest.cxx
+++ b/vcl/qa/cppunit/ScanlineToolsTest.cxx
@@ -42,9 +42,9 @@ void ScanlineToolsTest::ScanlineTransformer_32_ARGB()
     pScanlineTransformer->startLine(aScanLine.data());
 
     std::vector<Color> aColors{
-        Color(ColorTransparency, 0, 10, 250, 120),   Color(ColorTransparency, 50, 30, 230, 110),
-        Color(ColorTransparency, 100, 50, 210, 100), Color(ColorTransparency, 150, 70, 190, 90),
-        Color(ColorTransparency, 200, 90, 170, 80),
+        Color(ColorAlpha, 255, 10, 250, 120), Color(ColorAlpha, 205, 30, 230, 110),
+        Color(ColorAlpha, 155, 50, 210, 100), Color(ColorAlpha, 105, 70, 190, 90),
+        Color(ColorAlpha, 55, 90, 170, 80),
     };
 
     for (Color const& aColor : aColors)
@@ -52,8 +52,8 @@ void ScanlineToolsTest::ScanlineTransformer_32_ARGB()
         pScanlineTransformer->writePixel(aColor);
     }
 
-    std::vector<sal_uInt8> aExpectedBytes{ 0,   10,  250, 120, 50,  30, 230, 110, 100, 50,
-                                           210, 100, 150, 70,  190, 90, 200, 90,  170, 80 };
+    std::vector<sal_uInt8> aExpectedBytes{ 255, 10,  250, 120, 205, 30, 230, 110, 155, 50,
+                                           210, 100, 105, 70,  190, 90, 55,  90,  170, 80 };
 
     for (size_t i = 0; i < aScanLine.size(); ++i)
     {
diff --git a/vcl/qt5/Qt5Graphics_GDI.cxx b/vcl/qt5/Qt5Graphics_GDI.cxx
index a40a96e9fb29..5c4db9ecceb3 100644
--- a/vcl/qt5/Qt5Graphics_GDI.cxx
+++ b/vcl/qt5/Qt5Graphics_GDI.cxx
@@ -592,7 +592,7 @@ static bool getAlphaImage(const SalBitmap& rSourceBitmap, const SalBitmap& rAlph
             uchar* image_line = rAlphaImage.scanLine(y);
             const uchar* alpha_line = pAlpha->scanLine(y);
             for (int x = 0; x < rAlphaImage.width(); ++x, image_line += 4)
-                image_line[3] = 255 - alpha_line[x];
+                image_line[3] = alpha_line[x];
         }
     }
     else
diff --git a/vcl/skia/salbmp.cxx b/vcl/skia/salbmp.cxx
index e89a824f0d84..5d56abecbe79 100644
--- a/vcl/skia/salbmp.cxx
+++ b/vcl/skia/salbmp.cxx
@@ -1243,7 +1243,7 @@ OString SkiaSalBitmap::GetAlphaImageKey() const
     {
         std::stringstream ss;
         ss << std::hex << std::setfill('0') << std::setw(2)
-           << static_cast<int>(255 - SkColorGetA(fromEraseColorToAlphaImageColor(mEraseColor)));
+           << static_cast<int>(SkColorGetA(fromEraseColorToAlphaImageColor(mEraseColor)));
         return OStringLiteral("E") + ss.str().c_str();
     }
     return OStringLiteral("I") + OString::number(GetAlphaSkImage()->uniqueID());
diff --git a/vcl/source/bitmap/BitmapEx.cxx b/vcl/source/bitmap/BitmapEx.cxx
index 65698b6bbad9..c75aa12ed27b 100644
--- a/vcl/source/bitmap/BitmapEx.cxx
+++ b/vcl/source/bitmap/BitmapEx.cxx
@@ -1588,7 +1588,7 @@ void BitmapEx::AdjustTransparency(sal_uInt8 cTrans)
                 for( tools::Long nX = 0; nX < nWidth; nX++ )
                 {
                     nNewTrans = nTrans + *pAScan;
-                    *pAScan++ = static_cast<sal_uInt8>( ( nNewTrans & 0xffffff00 ) ? 255 : nNewTrans );
+                    *pAScan++ = static_cast<sal_uInt8>( ( nNewTrans & 0xffffff00 ) ? 0 : (255 - nNewTrans) );
                 }
             }
         }
diff --git a/vcl/source/gdi/gdimtf.cxx b/vcl/source/gdi/gdimtf.cxx
index e42e7feedb87..96df06275afc 100644
--- a/vcl/source/gdi/gdimtf.cxx
+++ b/vcl/source/gdi/gdimtf.cxx
@@ -1751,7 +1751,7 @@ Color GDIMetaFile::ImplColConvertFnc( const Color& rColor, const void* pColParam
     if( MtfConversion::N1BitThreshold == static_cast<const ImplColConvertParam*>(pColParam)->eConversion )
         cLum = ( cLum < 128 ) ? 0 : 255;
 
-    return Color( ColorTransparency, 255 - rColor.GetAlpha(), cLum, cLum, cLum );
+    return Color( ColorAlpha, rColor.GetAlpha(), cLum, cLum, cLum );
 }
 
 BitmapEx GDIMetaFile::ImplBmpConvertFnc( const BitmapEx& rBmpEx, const void* pBmpParam )
diff --git a/vcl/source/helper/canvasbitmap.cxx b/vcl/source/helper/canvasbitmap.cxx
index 9cef26b7a19b..97a1293bfad7 100644
--- a/vcl/source/helper/canvasbitmap.cxx
+++ b/vcl/source/helper/canvasbitmap.cxx
@@ -564,7 +564,8 @@ uno::Sequence< sal_Int8 > SAL_CALL VclCanvasBitmap::getPixel( rendering::Integer
         {
             // input less than a byte - copy via GetPixel()
             *pOutBuf++ = m_pBmpAcc->GetPixelIndex(pos.Y,pos.X);
-            *pOutBuf   = m_pAlphaAcc->GetPixelIndex(pos.Y,pos.X);
+            // convert alpha to transparency to preserve UNO compat
+            *pOutBuf   = 255 - m_pAlphaAcc->GetPixelIndex(pos.Y,pos.X);
         }
         else
         {
@@ -574,7 +575,8 @@ uno::Sequence< sal_Int8 > SAL_CALL VclCanvasBitmap::getPixel( rendering::Integer
             // input integer multiple of byte - copy directly
             memcpy(pOutBuf, pScan+nScanlineLeftOffset, nNonAlphaBytes );
             pOutBuf += nNonAlphaBytes;
-            *pOutBuf++ = m_pAlphaAcc->GetPixelIndex(pos.Y,pos.X);
+            // convert alpha to transparency to preserve UNO compat
+            *pOutBuf++ = 255 - m_pAlphaAcc->GetPixelIndex(pos.Y,pos.X);
         }
     }
 
@@ -1320,7 +1322,7 @@ uno::Sequence< ::sal_Int8 > SAL_CALL VclCanvasBitmap::convertIntegerFromARGB( co
 
             m_pBmpAcc->SetPixelOnData(pColors,i,aCol2);
             pColors   += nNonAlphaBytes;
-            *pColors++ = 255 - toByteColor(rgbColor[i].Alpha);
+            *pColors++ = toByteColor(rgbColor[i].Alpha);
         }
     }
     else
@@ -1370,7 +1372,7 @@ uno::Sequence< ::sal_Int8 > SAL_CALL VclCanvasBitmap::convertIntegerFromPARGB( c
 
             m_pBmpAcc->SetPixelOnData(pColors,i,aCol2);
             pColors   += nNonAlphaBytes;
-            *pColors++ = 255 - toByteColor(nAlpha);
+            *pColors++ = toByteColor(nAlpha);
         }
     }
     else
diff --git a/vcl/source/opengl/OpenGLHelper.cxx b/vcl/source/opengl/OpenGLHelper.cxx
index 82e01da1dc8d..2d9d3ce8c713 100644
--- a/vcl/source/opengl/OpenGLHelper.cxx
+++ b/vcl/source/opengl/OpenGLHelper.cxx
@@ -597,7 +597,7 @@ BitmapEx OpenGLHelper::ConvertBufferToBitmapEx(const sal_uInt8* const pBuffer, t
                 *pScan++ = pBuffer[nCurPos+2];
 
                 nCurPos += 3;
-                *pAlphaScan++ = static_cast<sal_uInt8>( 255 - pBuffer[nCurPos++] );
+                *pAlphaScan++ = pBuffer[nCurPos++];
             }
         }
     }