do not smoothscale if not changing pixel size

Flipping or rotating are simple operations in this regard. This saves
some CPU time in raster mode, and for the upcoming chrome/m90 release
this also prevents a failure in
BackendTest::testDrawTransformedBitmapExAlpha() when rotating.

Change-Id: I51890ac19b0bd5312fcf9c7bb8fe519dc10dc007
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/111771
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

3 files changed, 57 insertions, 3 deletions

diff --git a/vcl/inc/skia/utils.hxx b/vcl/inc/skia/utils.hxx
index 7da858ab1fff..b5412e9f9479 100644
--- a/vcl/inc/skia/utils.hxx
+++ b/vcl/inc/skia/utils.hxx
@@ -26,6 +26,7 @@
 #include <driverblocklist.hxx>
 
 #include <SkRegion.h>
+#include <SkSurface.h>
 #include <tools/sk_app/VulkanWindowContext.h>
 
 namespace SkiaHelper
@@ -94,7 +95,13 @@ inline DriverBlocklist::DeviceVendor getVendor()
     return DriverBlocklist::GetVendorFromId(vendorId);
 }
 
-} // namespace
+} // namespace SkiaHelper
+
+// For unittests.
+namespace SkiaTests
+{
+VCL_DLLPUBLIC bool matrixNeedsHighQuality(const SkMatrix& matrix);
+}
 
 template <typename charT, typename traits>
 inline std::basic_ostream<charT, traits>& operator<<(std::basic_ostream<charT, traits>& stream,
diff --git a/vcl/qa/cppunit/skia/skia.cxx b/vcl/qa/cppunit/skia/skia.cxx
index a84cb7d19907..6b18967f0590 100644
--- a/vcl/qa/cppunit/skia/skia.cxx
+++ b/vcl/qa/cppunit/skia/skia.cxx
@@ -17,6 +17,7 @@
 #include <vcl/skia/SkiaHelper.hxx>
 
 #include <skia/salbmp.hxx>
+#include <skia/utils.hxx>
 #include <bitmap/BitmapWriteAccess.hxx>
 
 // This tests backends that use Skia (i.e. intentionally not the svp one, which is the default.)
@@ -37,6 +38,7 @@ public:
     void testInterpretAs8Bit();
     void testAlphaBlendWith();
     void testBitmapCopyOnWrite();
+    void testMatrixQuality();
     void testTdf137329();
 
     CPPUNIT_TEST_SUITE(SkiaTest);
@@ -45,6 +47,7 @@ public:
     CPPUNIT_TEST(testInterpretAs8Bit);
     CPPUNIT_TEST(testAlphaBlendWith);
     CPPUNIT_TEST(testBitmapCopyOnWrite);
+    CPPUNIT_TEST(testMatrixQuality);
     CPPUNIT_TEST(testTdf137329);
     CPPUNIT_TEST_SUITE_END();
 
@@ -307,8 +310,25 @@ void SkiaTest::testBitmapCopyOnWrite()
     CPPUNIT_ASSERT(bitmap.unittestGetAlphaImage() != oldAlphaImage);
 }
 
+void SkiaTest::testMatrixQuality()
+{
+    if (!SkiaHelper::isVCLSkiaEnabled())
+        return;
+    // Not changing the size (but possibly rotated/flipped) does not need high quality transformations.
+    CPPUNIT_ASSERT(!SkiaTests::matrixNeedsHighQuality(SkMatrix()));
+    CPPUNIT_ASSERT(!SkiaTests::matrixNeedsHighQuality(SkMatrix::RotateDeg(90)));
+    CPPUNIT_ASSERT(!SkiaTests::matrixNeedsHighQuality(SkMatrix::RotateDeg(180)));
+    CPPUNIT_ASSERT(!SkiaTests::matrixNeedsHighQuality(SkMatrix::RotateDeg(270)));
+    CPPUNIT_ASSERT(!SkiaTests::matrixNeedsHighQuality(SkMatrix::Scale(1, -1)));
+    CPPUNIT_ASSERT(SkiaTests::matrixNeedsHighQuality(SkMatrix::Scale(0, -1)));
+    CPPUNIT_ASSERT(SkiaTests::matrixNeedsHighQuality(SkMatrix::Scale(2, 1)));
+    CPPUNIT_ASSERT(SkiaTests::matrixNeedsHighQuality(SkMatrix::RotateDeg(89)));
+}
+
 void SkiaTest::testTdf137329()
 {
+    if (!SkiaHelper::isVCLSkiaEnabled())
+        return;
     // Draw a filled polygon in the entire device, with AA enabled.
     // All pixels in the device should be black, even those at edges (i.e. not affected by AA).
     ScopedVclPtr<VirtualDevice> device = VclPtr<VirtualDevice>::Create(DeviceFormat::DEFAULT);
diff --git a/vcl/skia/gdiimpl.cxx b/vcl/skia/gdiimpl.cxx
index d8ddf48536c0..c511b2ef2f45 100644
--- a/vcl/skia/gdiimpl.cxx
+++ b/vcl/skia/gdiimpl.cxx
@@ -1766,6 +1766,33 @@ bool SkiaSalGraphicsImpl::hasFastDrawTransformedBitmap() const
     return true;
 }
 
+// Whether applying matrix needs image smoothing for the transformation.
+static bool matrixNeedsHighQuality(const SkMatrix& matrix)
+{
+    if (matrix.isIdentity())
+        return false;
+    if (matrix.isScaleTranslate())
+    {
+        if (abs(matrix.getScaleX()) == 1 && abs(matrix.getScaleY()) == 1)
+            return false; // Only at most flipping and keeping the size.
+        return true;
+    }
+    assert(!matrix.hasPerspective()); // we do not use this
+    if (matrix.getScaleX() == 0 && matrix.getScaleY() == 0)
+    {
+        // Rotating 90 or 270 degrees while keeping the size.
+        if ((matrix.getSkewX() == 1 && matrix.getSkewY() == -1)
+            || (matrix.getSkewX() == -1 && matrix.getSkewY() == 1))
+            return false;
+    }
+    return true;
+}
+
+namespace SkiaTests
+{
+bool matrixNeedsHighQuality(const SkMatrix& matrix) { return ::matrixNeedsHighQuality(matrix); }
+}
+
 bool SkiaSalGraphicsImpl::drawTransformedBitmap(const basegfx::B2DPoint& rNull,
                                                 const basegfx::B2DPoint& rX,
                                                 const basegfx::B2DPoint& rY,
@@ -1816,7 +1843,7 @@ bool SkiaSalGraphicsImpl::drawTransformedBitmap(const basegfx::B2DPoint& rNull,
         SkAutoCanvasRestore autoRestore(canvas, true);
         canvas->concat(matrix);
         SkPaint paint;
-        if (!matrix.isTranslate())
+        if (matrixNeedsHighQuality(matrix))
             paint.setFilterQuality(kHigh_SkFilterQuality);
         if (fAlpha == 1.0)
             canvas->drawImage(imageToDraw, 0, 0, &paint);
@@ -1842,7 +1869,7 @@ bool SkiaSalGraphicsImpl::drawTransformedBitmap(const basegfx::B2DPoint& rNull,
         SkAutoCanvasRestore autoRestore(canvas, true);
         canvas->concat(matrix);
         SkPaint paint;
-        if (!matrix.isTranslate())
+        if (matrixNeedsHighQuality(matrix))
             paint.setFilterQuality(kHigh_SkFilterQuality);
         if (pSkiaAlphaBitmap)
         {