SkCanvas::drawPaint() -> drawRect(), where applicable, and fix matrix

It makes the code a bit simpler. Also fix the matrix used
in SkiaSalGraphicsImpl::drawShader(), plus add asserts to verify
it's correct.

Change-Id: Ia6692ad90e822e6e44028b280dc2faaac06959a5
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/103743
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
(cherry picked from commit c1206e12eab237ffa7dde728da5bf1883a05ddb0)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/103791
Reviewed-by: Caolán McNamara <caolanm@redhat.com>

1 files changed, 14 insertions, 12 deletions

diff --git a/vcl/skia/gdiimpl.cxx b/vcl/skia/gdiimpl.cxx
index a4f0d5eb1a5d..fa2f386d6c35 100644
--- a/vcl/skia/gdiimpl.cxx
+++ b/vcl/skia/gdiimpl.cxx
@@ -1626,17 +1626,21 @@ void SkiaSalGraphicsImpl::drawShader(const SalTwoRect& rPosAry, const sk_sp<SkSh
     if (rPosAry.mnSrcWidth != rPosAry.mnDestWidth || rPosAry.mnSrcHeight != rPosAry.mnDestHeight)
         paint.setFilterQuality(kHigh_SkFilterQuality);
     SkCanvas* canvas = getDrawCanvas();
-    // SkCanvas::drawShader() cannot do rectangles, so clip to destination and use a matrix
-    // to map from source.
-    SkMatrix matrix;
+    // Scaling needs to be done explicitly using a matrix.
     SkAutoCanvasRestore autoRestore(canvas, true);
-    canvas->clipRect(destinationRect);
-    matrix.set(SkMatrix::kMScaleX, 1.0 * rPosAry.mnDestWidth / rPosAry.mnSrcWidth);
-    matrix.set(SkMatrix::kMScaleY, 1.0 * rPosAry.mnDestHeight / rPosAry.mnSrcHeight);
-    matrix.set(SkMatrix::kMTransX, rPosAry.mnDestX - rPosAry.mnSrcX);
-    matrix.set(SkMatrix::kMTransY, rPosAry.mnDestY - rPosAry.mnSrcY);
+    SkMatrix matrix = SkMatrix::Translate(rPosAry.mnDestX, rPosAry.mnDestY)
+                      * SkMatrix::Scale(1.0 * rPosAry.mnDestWidth / rPosAry.mnSrcWidth,
+                                        1.0 * rPosAry.mnDestHeight / rPosAry.mnSrcHeight)
+                      * SkMatrix::Translate(-rPosAry.mnSrcX, -rPosAry.mnSrcY);
+    assert(matrix.mapXY(rPosAry.mnSrcX, rPosAry.mnSrcY)
+           == SkPoint::Make(rPosAry.mnDestX, rPosAry.mnDestY));
+    assert(matrix.mapXY(rPosAry.mnSrcX + rPosAry.mnSrcWidth, rPosAry.mnSrcY + rPosAry.mnSrcHeight)
+           == SkPoint::Make(rPosAry.mnDestX + rPosAry.mnDestWidth,
+                            rPosAry.mnDestY + rPosAry.mnDestHeight));
     canvas->concat(matrix);
-    canvas->drawPaint(paint);
+    SkRect sourceRect
+        = SkRect::MakeXYWH(rPosAry.mnSrcX, rPosAry.mnSrcY, rPosAry.mnSrcWidth, rPosAry.mnSrcHeight);
+    canvas->drawRect(sourceRect, paint);
     postDraw();
 }
 
@@ -1705,12 +1709,10 @@ bool SkiaSalGraphicsImpl::drawTransformedBitmap(const basegfx::B2DPoint& rNull,
         paint.setFilterQuality(kHigh_SkFilterQuality);
         if (pSkiaAlphaBitmap)
         {
-            // SkCanvas::drawPaint() cannot do rectangles, so clip (is transformed by the matrix too).
-            canvas->clipRect(SkRect::MakeWH(aSize.Width(), aSize.Height()));
             paint.setShader(SkShaders::Blend(SkBlendMode::kDstOut, // VCL alpha is one-minus-alpha.
                                              rSkiaBitmap.GetSkImage()->makeShader(),
                                              pSkiaAlphaBitmap->GetAlphaSkImage()->makeShader()));
-            canvas->drawPaint(paint);
+            canvas->drawRect(SkRect::MakeWH(aSize.Width(), aSize.Height()), paint);
         }
         else
         {