blink: Add backdrop-filter support

Source/modules/canvas2d/CanvasRenderingContext2DState.cpp

Index: Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
diff --git a/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp b/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
index 94b6d969cc35ec778d0894bd298375ebb4331097..b2b880cfb8c53847e32ca257f772c60944cffe1e 100644
--- a/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
+++ b/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
@@ -36,6 +36,7 @@ CanvasRenderingContext2DState::CanvasRenderingContext2DState()
     , m_lineDashOffset(0)
     , m_unparsedFont(defaultFont)
     , m_unparsedFilter(defaultFilter)
+    , m_unparsedBackdropFilter(defaultFilter)
     , m_textAlign(StartTextAlign)
     , m_textBaseline(AlphabeticTextBaseline)
     , m_direction(DirectionInherit)
@@ -85,8 +86,11 @@ CanvasRenderingContext2DState::CanvasRenderingContext2DState(const CanvasRenderi
     , m_unparsedFont(other.m_unparsedFont)
     , m_font(other.m_font)
     , m_unparsedFilter(other.m_unparsedFilter)
+    , m_unparsedBackdropFilter(other.m_unparsedBackdropFilter)
     , m_filterValue(other.m_filterValue)
     , m_resolvedFilter(other.m_resolvedFilter)
+    , m_backdropFilterValue(other.m_backdropFilterValue)
+    , m_resolvedBackdropFilter(other.m_resolvedBackdropFilter)
     , m_textAlign(other.m_textAlign)
     , m_textBaseline(other.m_textBaseline)
     , m_direction(other.m_direction)
@@ -172,6 +176,7 @@ void CanvasRenderingContext2DState::fontsNeedUpdate(CSSFontSelector* fontSelecto
     // FIXME: We only really need to invalidate the resolved filter if the font
     // update above changed anything and the filter uses font-dependent units.
     m_resolvedFilter.clear();
+    m_resolvedBackdropFilter.clear(); // TODO(hendrikw): Not so sure if this is needed.
 }
 
 DEFINE_TRACE(CanvasRenderingContext2DState)
@@ -179,6 +184,7 @@ DEFINE_TRACE(CanvasRenderingContext2DState)
     visitor->trace(m_strokeStyle);
     visitor->trace(m_fillStyle);
     visitor->trace(m_filterValue);
+    visitor->trace(m_backdropFilterValue);
     CSSFontSelectorClient::trace(visitor);
 }
 
@@ -307,6 +313,7 @@ void CanvasRenderingContext2DState::setFont(const Font& font, CSSFontSelector* s
     // FIXME: We only really need to invalidate the resolved filter if it
     // uses font-relative units.
     m_resolvedFilter.clear();
+    m_resolvedBackdropFilter.clear(); // TODO(hendrikw): Not so sure if this is needed.
 }
 
 const Font& CanvasRenderingContext2DState::font() const
@@ -355,6 +362,36 @@ SkImageFilter* CanvasRenderingContext2DState::getFilter(Element* styleResolution
     return m_resolvedFilter.get();
 }
 
+SkImageFilter* CanvasRenderingContext2DState::getBackdropFilter(Element* styleResolutionHost, const Font& font) const
+{
+    // TODO(hendrikw): Better understand what this function is doing and determine if we can reuse getFilter,
+    // of if this function needs to be modified.
+    if (!m_backdropFilterValue)
+        return nullptr;
+
+    if (!m_resolvedBackdropFilter) {
+        RefPtr<ComputedStyle> filterStyle = ComputedStyle::create();
+        // Must set font in case the filter uses any font-relative units (em, ex)
+        filterStyle->setFont(font);
+
+        StyleResolverState resolverState(styleResolutionHost->document(), styleResolutionHost, filterStyle.get());
+        resolverState.setStyle(filterStyle);
+
+        // TODO(junov): crbug.com/502877 Feed m_fillStyle and m_strokeStyle into FillPaint and
+        // StrokePaint respectively for filters that reference SVG.
+        StyleBuilder::applyProperty(CSSPropertyBackdropFilter, resolverState, m_backdropFilterValue.get());
+        RefPtrWillBeRawPtr<FilterEffectBuilder> filterEffectBuilder = FilterEffectBuilder::create();
+        const float effectiveZoom = 1.0f; // Deliberately ignore zoom on the canvas element
+        filterEffectBuilder->build(styleResolutionHost, filterStyle->filter(), effectiveZoom);
+
+        SkiaImageFilterBuilder imageFilterBuilder;
+        RefPtrWillBeRawPtr<FilterEffect> lastEffect = filterEffectBuilder->lastEffect();
+        m_resolvedBackdropFilter = imageFilterBuilder.build(lastEffect.get(), ColorSpaceDeviceRGB);
+    }
+
+    return m_resolvedBackdropFilter.get();
+}
+
 SkDrawLooper* CanvasRenderingContext2DState::emptyDrawLooper() const
 {
     if (!m_emptyDrawLooper) {
@@ -441,6 +478,12 @@ void CanvasRenderingContext2DState::setFilter(PassRefPtrWillBeRawPtr<CSSValue> f
     m_resolvedFilter.clear();
 }
 
+void CanvasRenderingContext2DState::setBackdropFilter(PassRefPtrWillBeRawPtr<CSSValue> filterValue)
+{
+    m_backdropFilterValue = filterValue;
+    m_resolvedBackdropFilter.clear();
+}
+
 void CanvasRenderingContext2DState::setGlobalComposite(SkXfermode::Mode mode)
 {
     m_strokePaint.setXfermodeMode(mode);