[Skia] Implement inset shadows

https://bugs.webkit.org/show_bug.cgi?id=269714

Reviewed by Carlos Garcia Campos.

Move the drop shadow filter creation into a helper method, and refactor
all callers of GraphicsContextSkia::createFillPaint() to manually create
and apply a drop shadow. The helper method returns nullptr if there is
no shadow, or if the shadow is effectively hidden, following Cairo's
optimization.

Add a selector enum for inset and outset shadows, used by the helper
method aforementioned, and handle the case for both inset and outset
shadows. The outset shadow case is just what was there before.

The inset shadow case is a combination of two image filters. One creates
a black shadow with the drop shadow parameters, and uses it as a mask to
apply a color blend. The color blend is what uses the actual drop shadow
color, and blends it with the SrcIn mode, which effectively inverts the
drop shadow based on the pixel opacity.

The only place in code that interprets GraphicsContext.dropShadow() as
an inset shadow is inside GraphicsContext::fillRectWithRoundedHole(),
which is implemented in this commit using SkCanvas::drawDRRect().

* Source/WebCore/platform/graphics/skia/FontCascadeSkia.cpp:
(WebCore::FontCascade::drawGlyphs):
* Source/WebCore/platform/graphics/skia/GraphicsContextSkia.cpp:
(WebCore::GraphicsContextSkia::drawNativeImageInternal):
(WebCore::GraphicsContextSkia::fillPath):
(WebCore::GraphicsContextSkia::createDropShadowFilter const):
(WebCore::GraphicsContextSkia::createFillPaint const):
(WebCore::GraphicsContextSkia::fillRect):
(WebCore::GraphicsContextSkia::fillRoundedRectImpl):
(WebCore::GraphicsContextSkia::fillRectWithRoundedHole):
* Source/WebCore/platform/graphics/skia/GraphicsContextSkia.h:

Canonical link: https://commits.webkit.org/275093@main

Source/WebCore/platform/graphics/skia/FontCascadeSkia.cpp

@@ -51,7 +51,9 @@ void FontCascade::drawGlyphs(GraphicsContext& graphicsContext, const Font& font,
     }
     auto blob = builder.make();
     auto* canvas = graphicsContext.platformContext();
-    canvas->drawTextBlob(blob, SkFloatToScalar(position.x()), SkFloatToScalar(position.y()), static_cast<GraphicsContextSkia*>(&graphicsContext)->createFillPaint());
+    SkPaint paint = static_cast<GraphicsContextSkia*>(&graphicsContext)->createFillPaint();
+    paint.setImageFilter(static_cast<GraphicsContextSkia*>(&graphicsContext)->createDropShadowFilterIfNeeded(GraphicsContextSkia::ShadowStyle::Outset));
+    canvas->drawTextBlob(blob, SkFloatToScalar(position.x()), SkFloatToScalar(position.y()), paint);
 }
 
 bool FontCascade::canReturnFallbackFontsForComplexText()

Source/WebCore/platform/graphics/skia/GraphicsContextSkia.cpp

@@ -34,6 +34,7 @@
 #include "ImageBuffer.h"
 #include "IntRect.h"
 #include "NotImplemented.h"
+#include <skia/core/SkColorFilter.h>
 #include <skia/core/SkImage.h>
 #include <skia/core/SkPath.h>
 #include <skia/core/SkPathEffect.h>
@@ -230,6 +231,7 @@ void GraphicsContextSkia::drawNativeImageInternal(NativeImage& nativeImage, cons
     auto normalizedDestRect = normalizeRect(destRect);
     SkPaint paint = createFillPaint();
     paint.setBlendMode(toSkiaBlendMode(options.compositeOperator(), options.blendMode()));
+    paint.setImageFilter(createDropShadowFilterIfNeeded(ShadowStyle::Outset));
     canvas().drawImageRect(image, normalizedSrcRect, normalizedDestRect, toSkSamplingOptions(m_state.imageInterpolationQuality()), &paint, { });
 }
 
@@ -264,16 +266,19 @@ void GraphicsContextSkia::fillPath(const Path& path)
     if (path.isEmpty())
         return;
 
+    SkPaint paint = createFillPaint();
+    paint.setImageFilter(createDropShadowFilterIfNeeded(ShadowStyle::Outset));
+
     auto fillRule = toSkiaFillType(state().fillRule());
     auto& skiaPath= *path.platformPath();
     if (skiaPath.getFillType() == fillRule) {
-        canvas().drawPath(skiaPath, createFillPaint());
+        canvas().drawPath(skiaPath, paint);
         return;
     }
 
     auto skiaPathCopy = skiaPath;
     skiaPathCopy.setFillType(fillRule);
-    canvas().drawPath(skiaPathCopy, createFillPaint());
+    canvas().drawPath(skiaPathCopy, paint);
 }
 
 void GraphicsContextSkia::strokePath(const Path& path)
@@ -284,6 +289,42 @@ void GraphicsContextSkia::strokePath(const Path& path)
     canvas().drawPath(*path.platformPath(), createStrokePaint());
 }
 
+sk_sp<SkImageFilter> GraphicsContextSkia::createDropShadowFilterIfNeeded(ShadowStyle shadowStyle) const
+{
+    // FIXME: this does not handle state.shadowsIgnoreTransforms()
+
+    if (!hasDropShadow())
+        return nullptr;
+
+    const auto& shadow = dropShadow();
+    ASSERT(shadow);
+
+    const FloatSize& offset = shadow->offset;
+    auto shadowColor = shadow->color;
+
+    if (!shadowColor.isVisible() || (!offset.width() && !offset.height() && !shadow->radius))
+        return nullptr;
+
+    const auto& state = this->state();
+
+    const auto sigma = shadow->radius / 2.0;
+    auto globalAlpha = state.alpha();
+    if (globalAlpha < 1)
+        shadowColor = shadowColor.colorWithAlphaMultipliedBy(globalAlpha);
+    auto [r, g, b, a] = shadowColor.toColorTypeLossy<SRGBA<uint8_t>>().resolved();
+
+    switch (shadowStyle) {
+    case ShadowStyle::Outset:
+        return SkImageFilters::DropShadow(offset.width(), offset.height(), sigma, sigma, SkColorSetARGB(a, r, g, b), nullptr);
+    case ShadowStyle::Inset: {
+        auto dropShadow = SkImageFilters::DropShadowOnly(offset.width(), offset.height(), sigma, sigma, SK_ColorBLACK, nullptr);
+        return SkImageFilters::ColorFilter(SkColorFilters::Blend(SkColorSetARGB(a, r, g, b), SkBlendMode::kSrcIn), dropShadow);
+    }
+    }
+
+    return nullptr;
+}
+
 SkPaint GraphicsContextSkia::createFillPaint(std::optional<Color> fillColor) const
 {
     const auto& state = this->state();
@@ -306,21 +347,6 @@ SkPaint GraphicsContextSkia::createFillPaint(std::optional<Color> fillColor) con
         paint.setColor(SkColorSetARGB(a, r, g, b));
     }
 
-    // Outset shadow
-    // FIXME: Don't add the effect if the shadow is inset
-    if (hasDropShadow()) {
-        const auto shadow = dropShadow();
-        ASSERT(shadow);
-
-        const auto sigma = shadow->radius / 2.0;
-        auto globalAlpha = state.alpha();
-        auto shadowColor = shadow->color;
-        if (globalAlpha < 1)
-            shadowColor = shadowColor.colorWithAlphaMultipliedBy(globalAlpha);
-        auto [r, g, b, a] = shadowColor.toColorTypeLossy<SRGBA<uint8_t>>().resolved();
-        paint.setImageFilter(SkImageFilters::DropShadow(shadow->offset.width(), shadow->offset.height(), sigma, sigma, SkColorSetARGB(a, r, g, b), nullptr));
-    }
-
     return paint;
 }
 
@@ -357,12 +383,16 @@ SkPaint GraphicsContextSkia::createStrokePaint(std::optional<Color> strokeColor)
 
 void GraphicsContextSkia::fillRect(const FloatRect& boundaries)
 {
-    canvas().drawRect(boundaries, createFillPaint());
+    SkPaint paint = createFillPaint();
+    paint.setImageFilter(createDropShadowFilterIfNeeded(ShadowStyle::Outset));
+    canvas().drawRect(boundaries, paint);
 }
 
 void GraphicsContextSkia::fillRect(const FloatRect& boundaries, const Color& fillColor)
 {
-    canvas().drawRect(boundaries, createFillPaint(fillColor));
+    SkPaint paint = createFillPaint(fillColor);
+    paint.setImageFilter(createDropShadowFilterIfNeeded(ShadowStyle::Outset));
+    canvas().drawRect(boundaries, paint);
 }
 
 void GraphicsContextSkia::fillRect(const FloatRect&, Gradient&, const AffineTransform&)
@@ -620,14 +650,29 @@ void GraphicsContextSkia::fillRoundedRectImpl(const FloatRoundedRect& rect, cons
         { SkFloatToScalar(radii.bottomLeft().width()), SkFloatToScalar(radii.bottomLeft().height()) },
         { SkFloatToScalar(radii.bottomRight().width()), SkFloatToScalar(radii.bottomRight().height()) } };
     skRect.setRectRadii(rect.rect(), skRadii);
-    canvas().drawRRect(skRect, createFillPaint(color));
+
+    SkPaint paint = createFillPaint(color);
+    paint.setImageFilter(createDropShadowFilterIfNeeded(ShadowStyle::Outset));
+    canvas().drawRRect(skRect, paint);
 }
 
-void GraphicsContextSkia::fillRectWithRoundedHole(const FloatRect&, const FloatRoundedRect&, const Color& color)
+void GraphicsContextSkia::fillRectWithRoundedHole(const FloatRect& outerRect, const FloatRoundedRect& innerRRect, const Color& color)
 {
     if (!color.isValid())
         return;
-    notImplemented();
+
+    auto innerSkRect = SkRRect::MakeEmpty();
+    const auto& radii = innerRRect.radii();
+    SkVector skRadii[4] = {
+        { SkFloatToScalar(radii.topLeft().width()), SkFloatToScalar(radii.topLeft().height()) },
+        { SkFloatToScalar(radii.topRight().width()), SkFloatToScalar(radii.topRight().height()) },
+        { SkFloatToScalar(radii.bottomLeft().width()), SkFloatToScalar(radii.bottomLeft().height()) },
+        { SkFloatToScalar(radii.bottomRight().width()), SkFloatToScalar(radii.bottomRight().height()) } };
+    innerSkRect.setRectRadii(innerRRect.rect(), skRadii);
+
+    SkPaint paint = createFillPaint(color);
+    paint.setImageFilter(createDropShadowFilterIfNeeded(ShadowStyle::Inset));
+    canvas().drawDRRect(SkRRect::MakeRect(outerRect), innerSkRect, paint);
 }
 
 void GraphicsContextSkia::drawPattern(NativeImage& nativeImage, const FloatRect& destRect, const FloatRect& tileRect, const AffineTransform& patternTransform, const FloatPoint& phase, const FloatSize& spacing, ImagePaintingOptions options)

Source/WebCore/platform/graphics/skia/GraphicsContextSkia.h

@@ -99,6 +99,9 @@ class WEBCORE_EXPORT GraphicsContextSkia final : public GraphicsContext {
 
     RenderingMode renderingMode() const final;
 
+    enum class ShadowStyle : uint8_t { Outset, Inset };
+    sk_sp<SkImageFilter> createDropShadowFilterIfNeeded(ShadowStyle) const;
+
     SkPaint createFillPaint(std::optional<Color> fillColor = std::nullopt) const;
     SkPaint createStrokeStylePaint() const;
     SkPaint createStrokePaint(std::optional<Color> strokeColor = std::nullopt) const;