implement xor drawing directly using Skia (tdf#141090)

Up until now this has been implemented like in almost all other VCL
backends by manually xor-ing pixel values. But that required fetching
pixel values from the GPU in Vulkan mode, which is relatively slow.
Since some time Skia now has supported writing custom blending modes
using the SkBlender class, so it's now possible to drop the hack
and support xor drawing directly using a blender that does
the operation. This should be both faster and simpler.

Change-Id: Id751d0ed4034852ce68697ecf56cc6dfac95307f
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/126051
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

1 files changed, 23 insertions, 120 deletions

diff --git a/vcl/skia/gdiimpl.cxx b/vcl/skia/gdiimpl.cxx
index 63d588aa913e..f1670e8c6db5 100644
--- a/vcl/skia/gdiimpl.cxx
+++ b/vcl/skia/gdiimpl.cxx
@@ -263,7 +263,7 @@ SkiaSalGraphicsImpl::SkiaSalGraphicsImpl(SalGraphics& rParent, SalGeometryProvid
     , mIsGPU(false)
     , mLineColor(SALCOLOR_NONE)
     , mFillColor(SALCOLOR_NONE)
-    , mXorMode(false)
+    , mXorMode(XorMode::None)
     , mFlush(new SkiaFlushIdle(this))
     , mPendingOperationsToFlush(0)
     , mScaling(1)
@@ -540,8 +540,6 @@ void SkiaSalGraphicsImpl::flushDrawing()
     if (!mSurface)
         return;
     checkPendingDrawing();
-    if (mXorMode)
-        applyXor();
     mSurface->flushAndSubmit();
     mPendingOperationsToFlush = 0;
 }
@@ -553,7 +551,7 @@ void SkiaSalGraphicsImpl::setCanvasScalingAndClipping()
     // If HiDPI scaling is active, simply set a scaling matrix for the canvas. This means
     // that all painting can use VCL coordinates and they'll be automatically translated to mSurface
     // scaled coordinates. If that is not wanted, the scale() state needs to be temporarily unset.
-    // State such as mDirtyRect and mXorRegion is not scaled, the scaling matrix applies to clipping too,
+    // State such as mDirtyRect is not scaled, the scaling matrix applies to clipping too,
     // and the rest needs to be handled explicitly.
     // When reading mSurface contents there's no automatic scaling and it needs to be handled explicitly.
     canvas->save(); // keep the original state without any scaling
@@ -645,109 +643,14 @@ void SkiaSalGraphicsImpl::SetFillColor(Color nColor)
     mFillColor = nColor;
 }
 
-void SkiaSalGraphicsImpl::SetXORMode(bool set, bool)
+void SkiaSalGraphicsImpl::SetXORMode(bool set, bool invert)
 {
-    if (mXorMode == set)
+    XorMode newMode = set ? (invert ? XorMode::Invert : XorMode::Xor) : XorMode::None;
+    if (newMode == mXorMode)
         return;
     checkPendingDrawing();
-    SAL_INFO("vcl.skia.trace", "setxormode(" << this << "): " << set);
-    if (set)
-        mXorRegion.setEmpty();
-    else
-        applyXor();
-    mXorMode = set;
-}
-
-SkCanvas* SkiaSalGraphicsImpl::getXorCanvas()
-{
-    SkiaZone zone;
-    assert(mXorMode);
-    // Skia does not implement xor drawing, so we need to handle it manually by redirecting
-    // to a temporary SkBitmap and then doing the xor operation on the data ourselves.
-    // There's no point in using SkSurface for GPU, we'd immediately need to get the pixels back.
-    if (!mXorCanvas)
-    {
-        // Use unpremultiplied alpha (see xor applying in applyXor()).
-        if (!mXorBitmap.tryAllocPixels(mSurface->imageInfo().makeAlphaType(kUnpremul_SkAlphaType)))
-            abort();
-        mXorBitmap.eraseARGB(0, 0, 0, 0);
-        mXorCanvas = std::make_unique<SkCanvas>(mXorBitmap);
-        if (mScaling != 1)
-            mXorCanvas->scale(mScaling, mScaling);
-        setCanvasClipRegion(mXorCanvas.get(), mClipRegion);
-    }
-    return mXorCanvas.get();
-}
-
-void SkiaSalGraphicsImpl::applyXor()
-{
-    // Apply the result from the temporary bitmap manually. This is indeed
-    // slow, but it doesn't seem to be needed often and is optimized
-    // in each operation by extending mXorRegion with the area that should be
-    // updated.
-    assert(mXorMode);
-    if (mScaling != 1 && !mXorRegion.isEmpty())
-    {
-        // Scale mXorRegion to mSurface coordinates if needed.
-        std::vector<SkIRect> rects;
-        for (SkRegion::Iterator it(mXorRegion); !it.done(); it.next())
-            rects.push_back(scaleRect(it.rect(), mScaling));
-        mXorRegion.setRects(rects.data(), rects.size());
-    }
-    if (!mSurface || !mXorCanvas
-        || !mXorRegion.op(SkIRect::MakeXYWH(0, 0, mSurface->width(), mSurface->height()),
-                          SkRegion::kIntersect_Op))
-    {
-        mXorRegion.setEmpty();
-        return;
-    }
-    SAL_INFO("vcl.skia.trace", "applyxor(" << this << "): " << mXorRegion);
-    // Copy the surface contents to another pixmap.
-    SkBitmap surfaceBitmap;
-    // Use unpremultiplied alpha format, so that we do not have to do the conversions to get
-    // the RGB and back (Skia will do it when converting, but it'll be presumably faster at it).
-    if (!surfaceBitmap.tryAllocPixels(mSurface->imageInfo().makeAlphaType(kUnpremul_SkAlphaType)))
-        abort();
-    SkPaint paint;
-    paint.setBlendMode(SkBlendMode::kSrc); // copy as is
-    SkRect area = SkRect::Make(mXorRegion.getBounds());
-    {
-        SkCanvas canvas(surfaceBitmap);
-        canvas.drawImageRect(makeCheckedImageSnapshot(mSurface), area, area, SkSamplingOptions(),
-                             &paint, SkCanvas::kFast_SrcRectConstraint);
-    }
-    // xor to surfaceBitmap
-    assert(surfaceBitmap.info().alphaType() == kUnpremul_SkAlphaType);
-    assert(mXorBitmap.info().alphaType() == kUnpremul_SkAlphaType);
-    assert(surfaceBitmap.bytesPerPixel() == 4);
-    assert(mXorBitmap.bytesPerPixel() == 4);
-    for (SkRegion::Iterator it(mXorRegion); !it.done(); it.next())
-    {
-        for (int y = it.rect().top(); y < it.rect().bottom(); ++y)
-        {
-            uint8_t* data = static_cast<uint8_t*>(surfaceBitmap.getAddr(it.rect().x(), y));
-            const uint8_t* xordata = static_cast<uint8_t*>(mXorBitmap.getAddr(it.rect().x(), y));
-            for (int x = 0; x < it.rect().width(); ++x)
-            {
-                *data++ ^= *xordata++;
-                *data++ ^= *xordata++;
-                *data++ ^= *xordata++;
-                // alpha is not xor-ed
-                data++;
-                xordata++;
-            }
-        }
-    }
-    surfaceBitmap.notifyPixelsChanged();
-    surfaceBitmap.setImmutable();
-    // Copy without any clipping or scaling.
-    resetCanvasScalingAndClipping();
-    mSurface->getCanvas()->drawImageRect(surfaceBitmap.asImage(), area, area, SkSamplingOptions(),
-                                         &paint, SkCanvas::kFast_SrcRectConstraint);
-    setCanvasScalingAndClipping();
-    mXorCanvas.reset();
-    mXorBitmap.reset();
-    mXorRegion.setEmpty();
+    SAL_INFO("vcl.skia.trace", "setxormode(" << this << "): " << set << "/" << invert);
+    mXorMode = newMode;
 }
 
 void SkiaSalGraphicsImpl::SetROPLineColor(SalROPColor nROPColor)
@@ -796,8 +699,7 @@ void SkiaSalGraphicsImpl::drawPixel(tools::Long nX, tools::Long nY, Color nColor
     preDraw();
     SAL_INFO("vcl.skia.trace", "drawpixel(" << this << "): " << Point(nX, nY) << ":" << nColor);
     addUpdateRegion(SkRect::MakeXYWH(nX, nY, 1, 1));
-    SkPaint paint;
-    paint.setColor(toSkColor(nColor));
+    SkPaint paint = makePixelPaint(nColor);
     // Apparently drawPixel() is actually expected to set the pixel and not draw it.
     paint.setBlendMode(SkBlendMode::kSrc); // set as is, including alpha
     if (mScaling != 1 && isUnitTestRunning())
@@ -1290,7 +1192,7 @@ void SkiaSalGraphicsImpl::copyBits(const SalTwoRect& rPosAry, SalGraphics* pSrcG
     else
     {
         src = this;
-        assert(!mXorMode);
+        assert(mXorMode == XorMode::None);
     }
     auto srcDebug = [&]() -> std::string {
         if (src == this)
@@ -1309,7 +1211,7 @@ void SkiaSalGraphicsImpl::copyBits(const SalTwoRect& rPosAry, SalGraphics* pSrcG
 
 void SkiaSalGraphicsImpl::privateCopyBits(const SalTwoRect& rPosAry, SkiaSalGraphicsImpl* src)
 {
-    assert(!mXorMode);
+    assert(mXorMode == XorMode::None);
     addUpdateRegion(SkRect::MakeXYWH(rPosAry.mnDestX, rPosAry.mnDestY, rPosAry.mnDestWidth,
                                      rPosAry.mnDestHeight));
     SkPaint paint;
@@ -1499,7 +1401,7 @@ void SkiaSalGraphicsImpl::invert(basegfx::B2DPolygon const& rPoly, SalInvert eFl
 {
     preDraw();
     SAL_INFO("vcl.skia.trace", "invert(" << this << "): " << rPoly << ":" << int(eFlags));
-    assert(!mXorMode);
+    assert(mXorMode == XorMode::None);
     SkPath aPath;
     aPath.incReserve(rPoly.count());
     addPolygonToPath(rPoly, aPath);
@@ -1847,7 +1749,7 @@ void SkiaSalGraphicsImpl::drawImage(const SalTwoRect& rPosAry, const sk_sp<SkIma
     SkRect aDestinationRect = SkRect::MakeXYWH(rPosAry.mnDestX, rPosAry.mnDestY,
                                                rPosAry.mnDestWidth, rPosAry.mnDestHeight);
 
-    SkPaint aPaint;
+    SkPaint aPaint = makeBitmapPaint();
     aPaint.setBlendMode(eBlendMode);
 
     preDraw();
@@ -1871,7 +1773,7 @@ void SkiaSalGraphicsImpl::drawShader(const SalTwoRect& rPosAry, const sk_sp<SkSh
     SkRect destinationRect = SkRect::MakeXYWH(rPosAry.mnDestX, rPosAry.mnDestY, rPosAry.mnDestWidth,
                                               rPosAry.mnDestHeight);
     addUpdateRegion(destinationRect);
-    SkPaint paint;
+    SkPaint paint = makeBitmapPaint();
     paint.setBlendMode(blendMode);
     paint.setShader(shader);
     SkCanvas* canvas = getDrawCanvas();
@@ -1994,12 +1896,13 @@ bool SkiaSalGraphicsImpl::drawTransformedBitmap(const basegfx::B2DPoint& rNull,
             // Specify sizes to scale the image size back if needed (because of mScaling).
             SkRect dstRect = SkRect::MakeWH(imageSize.Width(), imageSize.Height());
             SkRect srcRect = SkRect::MakeWH(imageToDraw->width(), imageToDraw->height());
-            canvas->drawImageRect(imageToDraw, srcRect, dstRect, samplingOptions, nullptr,
+            SkPaint paint = makeBitmapPaint();
+            canvas->drawImageRect(imageToDraw, srcRect, dstRect, samplingOptions, &paint,
                                   SkCanvas::kFast_SrcRectConstraint);
         }
         else
         {
-            SkPaint paint;
+            SkPaint paint = makeBitmapPaint();
             // Scale the image size back if needed.
             SkMatrix scale = SkMatrix::Scale(1.0 / mScaling, 1.0 / mScaling);
             paint.setShader(SkShaders::Blend(
@@ -2026,7 +1929,7 @@ bool SkiaSalGraphicsImpl::drawTransformedBitmap(const basegfx::B2DPoint& rNull,
             samplingOptions = makeSamplingOptions(BmpScaleFlag::BestQuality, matrix, mScaling);
         if (pSkiaAlphaBitmap)
         {
-            SkPaint paint;
+            SkPaint paint = makeBitmapPaint();
             paint.setShader(SkShaders::Blend(SkBlendMode::kDstOut, // VCL alpha is one-minus-alpha.
                                              rSkiaBitmap.GetSkShader(samplingOptions),
                                              pSkiaAlphaBitmap->GetAlphaSkShader(samplingOptions)));
@@ -2038,7 +1941,7 @@ bool SkiaSalGraphicsImpl::drawTransformedBitmap(const basegfx::B2DPoint& rNull,
         }
         else if (rSkiaBitmap.PreferSkShader() || fAlpha != 1.0)
         {
-            SkPaint paint;
+            SkPaint paint = makeBitmapPaint();
             paint.setShader(rSkiaBitmap.GetSkShader(samplingOptions));
             if (fAlpha != 1.0)
                 paint.setShader(
@@ -2048,7 +1951,8 @@ bool SkiaSalGraphicsImpl::drawTransformedBitmap(const basegfx::B2DPoint& rNull,
         }
         else
         {
-            canvas->drawImage(rSkiaBitmap.GetSkImage(), 0, 0, samplingOptions);
+            SkPaint paint = makeBitmapPaint();
+            canvas->drawImage(rSkiaBitmap.GetSkImage(), 0, 0, samplingOptions, &paint);
         }
     }
     postDraw();
@@ -2135,7 +2039,7 @@ bool SkiaSalGraphicsImpl::drawGradient(const tools::PolyPolygon& rPolyPolygon,
         shader = SkGradientShader::MakeRadial(center, radius, colors, pos, 2, SkTileMode::kClamp);
     }
 
-    SkPaint paint;
+    SkPaint paint = makeGradientPaint();
     paint.setAntiAlias(mParent.getAntiAlias());
     paint.setShader(shader);
     getDrawCanvas()->drawPath(path, paint);
@@ -2168,7 +2072,7 @@ bool SkiaSalGraphicsImpl::implDrawGradient(const basegfx::B2DPolyPolygon& rPolyP
     }
     sk_sp<SkShader> shader = SkGradientShader::MakeLinear(points, colors.data(), pos.data(),
                                                           colors.size(), SkTileMode::kDecal);
-    SkPaint paint;
+    SkPaint paint = makeGradientPaint();
     paint.setAntiAlias(mParent.getAntiAlias());
     paint.setShader(shader);
     getDrawCanvas()->drawPath(path, paint);
@@ -2229,8 +2133,7 @@ void SkiaSalGraphicsImpl::drawGenericLayout(const GenericSalLayout& layout, Colo
             glyphIds.data() + index, count * sizeof(SkGlyphID), glyphForms.data() + index,
             verticalRun ? verticalFont : font, SkTextEncoding::kGlyphID);
         addUpdateRegion(textBlob->bounds());
-        SkPaint paint;
-        paint.setColor(toSkColor(textColor));
+        SkPaint paint = makeTextPaint(textColor);
         getDrawCanvas()->drawTextBlob(textBlob, 0, 0, paint);
         pos = rangeEnd;
     }