tdf#144601 Qt fix creating QImage with alpha mask

Rechecking the QImage documentation, this actually can be easily
done; no more bit twiddling, which I got wrong to begin with.

LO's alpha mask is inverted to Qt's expectations, but we have
invertPixels() and then apply it with setAlphaChannel(). And we
can even set the fAlpha using setOpacity()!

Change-Id: If2030d3f87d3a4698d1cd9af005d307c2ee63061
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/135044
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>
Tested-by: Jenkins

1 files changed, 16 insertions, 50 deletions

diff --git a/vcl/qt5/QtGraphics_GDI.cxx b/vcl/qt5/QtGraphics_GDI.cxx
index f87de50827df..6849a3bc7bde 100644
--- a/vcl/qt5/QtGraphics_GDI.cxx
+++ b/vcl/qt5/QtGraphics_GDI.cxx
@@ -601,55 +601,24 @@ bool QtGraphicsBackend::blendAlphaBitmap(const SalTwoRect&, const SalBitmap& /*r
     return false;
 }
 
-static bool getAlphaImage(const SalBitmap& rSourceBitmap, const SalBitmap& rAlphaBitmap,
-                          QImage& rAlphaImage)
+static QImage getAlphaImage(const SalBitmap& rSourceBitmap, const SalBitmap& rAlphaBitmap)
 {
-    if (rAlphaBitmap.GetBitCount() != 8 && rAlphaBitmap.GetBitCount() != 1)
-    {
-        SAL_WARN("vcl.gdi", "unsupported alpha depth case: " << rAlphaBitmap.GetBitCount());
-        return false;
-    }
+    assert(rSourceBitmap.GetSize() == rAlphaBitmap.GetSize());
+    assert(rAlphaBitmap.GetBitCount() == 8 || rAlphaBitmap.GetBitCount() == 1);
 
-    const QImage* pBitmap = static_cast<const QtBitmap*>(&rSourceBitmap)->GetQImage();
-    const QImage* pAlpha = static_cast<const QtBitmap*>(&rAlphaBitmap)->GetQImage();
-    rAlphaImage = pBitmap->convertToFormat(Qt_DefaultFormat32);
+    QImage aAlphaMask = *static_cast<const QtBitmap*>(&rAlphaBitmap)->GetQImage();
+    aAlphaMask.invertPixels();
 
-    if (rAlphaBitmap.GetBitCount() == 8)
-    {
-        for (int y = 0; y < rAlphaImage.height(); ++y)
-        {
-            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];
-        }
-    }
-    else
-    {
-        for (int y = 0; y < rAlphaImage.height(); ++y)
-        {
-            uchar* image_line = rAlphaImage.scanLine(y);
-            const uchar* alpha_line = pAlpha->scanLine(y);
-            for (int x = 0; x < rAlphaImage.width(); ++x, image_line += 4)
-            {
-                if (x && !(x % 8))
-                    ++alpha_line;
-                if (0 != (*alpha_line & (1 << (7 - x % 8))))
-                    image_line[3] = 0;
-            }
-        }
-    }
-
-    return true;
+    const QImage* pBitmap = static_cast<const QtBitmap*>(&rSourceBitmap)->GetQImage();
+    QImage aImage = pBitmap->convertToFormat(Qt_DefaultFormat32);
+    aImage.setAlphaChannel(aAlphaMask);
+    return aImage;
 }
 
 bool QtGraphicsBackend::drawAlphaBitmap(const SalTwoRect& rPosAry, const SalBitmap& rSourceBitmap,
                                         const SalBitmap& rAlphaBitmap)
 {
-    QImage aImage;
-    if (!getAlphaImage(rSourceBitmap, rAlphaBitmap, aImage))
-        return false;
-    drawScaledImage(rPosAry, aImage);
+    drawScaledImage(rPosAry, getAlphaImage(rSourceBitmap, rAlphaBitmap));
     return true;
 }
 
@@ -659,20 +628,17 @@ bool QtGraphicsBackend::drawTransformedBitmap(const basegfx::B2DPoint& rNull,
                                               const SalBitmap& rSourceBitmap,
                                               const SalBitmap* pAlphaBitmap, double fAlpha)
 {
-    if (fAlpha != 1.0)
-        return false;
     QImage aImage;
-    if (pAlphaBitmap && !getAlphaImage(rSourceBitmap, *pAlphaBitmap, aImage))
-        return false;
+    if (!pAlphaBitmap)
+        aImage = *static_cast<const QtBitmap*>(&rSourceBitmap)->GetQImage();
     else
-    {
-        const QImage* pBitmap = static_cast<const QtBitmap*>(&rSourceBitmap)->GetQImage();
-        aImage = pBitmap->convertToFormat(Qt_DefaultFormat32);
-    }
+        aImage = getAlphaImage(rSourceBitmap, *pAlphaBitmap);
 
-    QtPainter aPainter(*this);
     const basegfx::B2DVector aXRel = rX - rNull;
     const basegfx::B2DVector aYRel = rY - rNull;
+
+    QtPainter aPainter(*this);
+    aPainter.setOpacity(fAlpha);
     aPainter.setTransform(QTransform(aXRel.getX() / aImage.width(), aXRel.getY() / aImage.width(),
                                      aYRel.getX() / aImage.height(), aYRel.getY() / aImage.height(),
                                      rNull.getX(), rNull.getY()));