[web-animations] implement correct accumulation support for the `filt…

…er` property

https://bugs.webkit.org/show_bug.cgi?id=248235

Reviewed by Tim Nguyen.

Implement the specific accumulation behavior for brightness(), contrast(), opacity()
and saturate() operations. We also ensure we have the correct clipping behavior for
various other operations since with accumulation support they could appear out of
bounds.

* LayoutTests/imported/w3c/web-platform-tests/web-animations/animation-model/animation-types/accumulation-per-property-001-expected.txt:
* LayoutTests/imported/w3c/web-platform-tests/web-animations/animation-model/keyframe-effects/effect-value-iteration-composite-operation-expected.txt:
* Source/WebCore/platform/graphics/filters/FilterOperation.cpp:
(WebCore::FilterOperation::blendAmounts const):
(WebCore::BasicColorMatrixFilterOperation::blend):
(WebCore::BasicComponentTransferFilterOperation::blend):
* Source/WebCore/platform/graphics/filters/FilterOperation.h:

Canonical link: https://commits.webkit.org/256952@main

LayoutTests/imported/w3c/web-platform-tests/web-animations/animation-model/animation-types/accumulation-per-property-001-expected.txt

@@ -197,7 +197,7 @@ PASS fill-rule (type: discrete) has testAccumulation function
 PASS fill-rule: "nonzero" onto "evenodd"
 PASS fill-rule: "evenodd" onto "nonzero"
 PASS filter (type: filterList) has testAccumulation function
-FAIL filter: same ordered filter functions assert_equals: The value should be blur(30px) brightness(0) at 0ms expected "blur(30px) brightness(0)" but got "blur(30px) brightness(0.4)"
+PASS filter: same ordered filter functions
 PASS filter: mismatched ordered filter functions
 PASS flex-basis (type: lengthPercentageOrCalc) has testAccumulation function
 PASS flex-basis: length

LayoutTests/imported/w3c/web-platform-tests/web-animations/animation-model/keyframe-effects/effect-value-iteration-composite-operation-expected.txt

@@ -11,10 +11,10 @@ PASS iteration composition of <calc()> value animation that the values can'tbe r
 FAIL iteration composition of opacity animation assert_equals: Animated opacity style at 50s of the third iteration expected "1" but got "0.9"
 PASS iteration composition of box-shadow animation
 PASS iteration composition of filter blur animation
-FAIL iteration composition of filter brightness for different unit animation assert_equals: Animated filter brightness style at 0s of the third iteration expected "brightness(2.6)" but got "brightness(4.6)"
-FAIL iteration composition of filter brightness animation assert_equals: Animated filter brightness style at 0s of the third iteration expected "brightness(0)" but got "brightness(2)"
+PASS iteration composition of filter brightness for different unit animation
+PASS iteration composition of filter brightness animation
 PASS iteration composition of filter drop-shadow animation
-FAIL iteration composition of same filter list animation assert_equals: Animated filter list at 0s of the third iteration expected "brightness(3) contrast(3)" but got "brightness(5) contrast(5)"
+PASS iteration composition of same filter list animation
 FAIL iteration composition of discrete filter list because of mismatch of the order assert_equals: Animated filter list at 0s of the third iteration expected "brightness(1) contrast(1)" but got "contrast(2) brightness(2)"
 FAIL iteration composition of different length filter list animation assert_equals: Animated filter list at 50s of the first iteration expected "sepia(0.5) contrast(1.5)" but got "sepia(1) contrast(2)"
 PASS iteration composition of transform(rotate) animation

Source/WebCore/platform/graphics/filters/FilterOperation.cpp

@@ -92,29 +92,53 @@ void ReferenceFilterOperation::loadExternalDocumentIfNeeded(CachedResourceLoader
     m_cachedSVGDocumentReference->load(cachedResourceLoader, options);
 }
 
+double FilterOperation::blendAmounts(double from, double to, const BlendingContext& context) const
+{
+    auto blendedAmount = [&]() {
+        if (context.compositeOperation == CompositeOperation::Accumulate) {
+            // The "initial value for interpolation" is 1 for brightness, contrast, opacity and saturate.
+            // Accumulation works differently for such operations per https://drafts.fxtf.org/filter-effects/#accumulation.
+            switch (m_type) {
+            case BRIGHTNESS:
+            case CONTRAST:
+            case OPACITY:
+            case SATURATE:
+                return from + to - 1;
+            default:
+                break;
+            }
+        }
+        return WebCore::blend(from, to, context);
+    }();
+
+    // Make sure blended values remain within bounds as specified by
+    // https://drafts.fxtf.org/filter-effects/#supported-filter-functions
+    switch (m_type) {
+    case GRAYSCALE:
+    case INVERT:
+    case OPACITY:
+    case SEPIA:
+        return std::clamp(blendedAmount, 0.0, 1.0);
+    case BRIGHTNESS:
+    case CONTRAST:
+    case SATURATE:
+        return std::max(blendedAmount, 0.0);
+    default:
+        return blendedAmount;
+    }
+}
+
 RefPtr<FilterOperation> BasicColorMatrixFilterOperation::blend(const FilterOperation* from, const BlendingContext& context, bool blendToPassthrough)
 {
     if (from && !from->isSameType(*this))
         return this;
-    
+
     if (blendToPassthrough)
         return BasicColorMatrixFilterOperation::create(WebCore::blend(m_amount, passthroughAmount(), context), m_type);
-        
+
     const BasicColorMatrixFilterOperation* fromOperation = downcast<BasicColorMatrixFilterOperation>(from);
     double fromAmount = fromOperation ? fromOperation->amount() : passthroughAmount();
-    double blendedAmount = WebCore::blend(fromAmount, m_amount, context);
-
-    switch (m_type) {
-    case GRAYSCALE:
-    case SEPIA:
-        blendedAmount = std::clamp(blendedAmount, 0.0, 1.0);
-        break;
-    case SATURATE:
-        blendedAmount = std::max(blendedAmount, 0.0);
-        break;
-    default:
-        break;
-    }
+    auto blendedAmount = blendAmounts(fromAmount, m_amount, context);
     return BasicColorMatrixFilterOperation::create(blendedAmount, m_type);
 }
 
@@ -183,20 +207,7 @@ RefPtr<FilterOperation> BasicComponentTransferFilterOperation::blend(const Filte
 
     const BasicComponentTransferFilterOperation* fromOperation = downcast<BasicComponentTransferFilterOperation>(from);
     double fromAmount = fromOperation ? fromOperation->amount() : passthroughAmount();
-    double blendedAmount = WebCore::blend(fromAmount, m_amount, context);
-
-    switch (m_type) {
-    case INVERT:
-    case OPACITY:
-        blendedAmount = std::clamp(blendedAmount, 0.0, 1.0);
-        break;
-    case BRIGHTNESS:
-    case CONTRAST:
-        blendedAmount = std::max(blendedAmount, 0.0);
-        break;
-    default:
-        break;
-    }
+    auto blendedAmount = blendAmounts(fromAmount, m_amount, context);
     return BasicComponentTransferFilterOperation::create(blendedAmount, m_type);
 }
 

Source/WebCore/platform/graphics/filters/FilterOperation.h

@@ -114,6 +114,8 @@ class FilterOperation : public ThreadSafeRefCounted<FilterOperation> {
     {
     }
 
+    double blendAmounts(double from, double to, const BlendingContext&) const;
+
     OperationType m_type;
 };