optimised Skia Invert() operation

which is not that important right now, but my upcoming
transparency->alpha patch will make more heavy use of Invert(),
and this change will reduce the cost of that

Change-Id: I53d8dfbf153f16f4d94022527c71d70d08392dfc
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/153857
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

1 files changed, 25 insertions, 0 deletions

diff --git a/vcl/skia/salbmp.cxx b/vcl/skia/salbmp.cxx
index 57cea14316c5..1ce85dd0e837 100644
--- a/vcl/skia/salbmp.cxx
+++ b/vcl/skia/salbmp.cxx
@@ -623,6 +623,31 @@ bool SkiaSalBitmap::AlphaBlendWith(const SalBitmap& rSalBmp)
     return true;
 }
 
+bool SkiaSalBitmap::Invert()
+{
+#ifdef DBG_UTIL
+    assert(mWriteAccessCount == 0);
+#endif
+    // Normally this would need to convert contents of mBuffer for all possible formats,
+    // so just let the VCL algorithm do it.
+    // Avoid the costly SkImage->buffer->SkImage conversion.
+    if (!mBuffer && mImage && !mEraseColorSet)
+    {
+        // This is 8-bit bitmap serving as alpha/transparency/mask, so the image itself needs no alpha.
+        sk_sp<SkSurface> surface = createSkSurface(mSize, kOpaque_SkAlphaType);
+        surface->getCanvas()->clear(SK_ColorWHITE);
+        SkPaint paint;
+        paint.setBlendMode(SkBlendMode::kDifference);
+        surface->getCanvas()->drawImage(
+            mImage, 0, 0, SkSamplingOptions(SkFilterMode::kLinear, SkMipmapMode::kLinear), &paint);
+        ResetToSkImage(makeCheckedImageSnapshot(surface));
+        DataChanged();
+        SAL_INFO("vcl.skia.trace", "invert(" << this << ")");
+        return true;
+    }
+    return false;
+}
+
 SkBitmap SkiaSalBitmap::GetAsSkBitmap() const
 {
 #ifdef DBG_UTIL