From cb268beaa9b159c19478d3b30a6504ca181dfabc Mon Sep 17 00:00:00 2001
From: Niklas von Hertzen <niklasvh@gmail.com>
Date: Tue, 29 Dec 2020 12:29:00 +0800
Subject: [PATCH] fix: opacity with overflow hidden (#2450)

---
 src/render/canvas/canvas-renderer.ts  |  7 +++++--
 src/render/effects.ts                 | 23 ++++++++++++++++-------
 src/render/stacking-context.ts        |  6 +++++-
 tests/reftests/overflow/overflow.html |  1 +
 4 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/src/render/canvas/canvas-renderer.ts b/src/render/canvas/canvas-renderer.ts
index 93ca92340..f6d3a4af1 100644
--- a/src/render/canvas/canvas-renderer.ts
+++ b/src/render/canvas/canvas-renderer.ts
@@ -22,7 +22,7 @@ import {contentBox} from '../box-sizing';
 import {CanvasElementContainer} from '../../dom/replaced-elements/canvas-element-container';
 import {SVGElementContainer} from '../../dom/replaced-elements/svg-element-container';
 import {ReplacedElementContainer} from '../../dom/replaced-elements/index';
-import {EffectTarget, IElementEffect, isClipEffect, isTransformEffect} from '../effects';
+import {EffectTarget, IElementEffect, isClipEffect, isOpacityEffect, isTransformEffect} from '../effects';
 import {contains} from '../../core/bitwise';
 import {calculateGradientDirection, calculateRadius, processColorStops} from '../../css/types/functions/gradient';
 import {FIFTY_PERCENT, getAbsoluteValue} from '../../css/types/length-percentage';
@@ -99,6 +99,10 @@ export class CanvasRenderer {
 
     applyEffect(effect: IElementEffect) {
         this.ctx.save();
+        if (isOpacityEffect(effect)) {
+            this.ctx.globalAlpha = effect.opacity;
+        }
+
         if (isTransformEffect(effect)) {
             this.ctx.translate(effect.offsetX, effect.offsetY);
             this.ctx.transform(
@@ -128,7 +132,6 @@ export class CanvasRenderer {
     async renderStack(stack: StackingContext) {
         const styles = stack.element.container.styles;
         if (styles.isVisible()) {
-            this.ctx.globalAlpha = styles.opacity;
             await this.renderStackContent(stack);
         }
     }
diff --git a/src/render/effects.ts b/src/render/effects.ts
index f9df190df..1bb428349 100644
--- a/src/render/effects.ts
+++ b/src/render/effects.ts
@@ -3,7 +3,8 @@ import {Path} from './path';
 
 export const enum EffectType {
     TRANSFORM = 0,
-    CLIP = 1
+    CLIP = 1,
+    OPACITY = 2
 }
 
 export const enum EffectTarget {
@@ -17,33 +18,41 @@ export interface IElementEffect {
 }
 
 export class TransformEffect implements IElementEffect {
-    readonly type: EffectType;
-    readonly target: number;
+    readonly type: EffectType = EffectType.TRANSFORM;
+    readonly target: number = EffectTarget.BACKGROUND_BORDERS | EffectTarget.CONTENT;
     readonly offsetX: number;
     readonly offsetY: number;
     readonly matrix: Matrix;
 
     constructor(offsetX: number, offsetY: number, matrix: Matrix) {
-        this.type = EffectType.TRANSFORM;
         this.offsetX = offsetX;
         this.offsetY = offsetY;
         this.matrix = matrix;
-        this.target = EffectTarget.BACKGROUND_BORDERS | EffectTarget.CONTENT;
     }
 }
 
 export class ClipEffect implements IElementEffect {
-    readonly type: EffectType;
+    readonly type: EffectType = EffectType.CLIP;
     readonly target: number;
     readonly path: Path[];
 
     constructor(path: Path[], target: EffectTarget) {
-        this.type = EffectType.CLIP;
         this.target = target;
         this.path = path;
     }
 }
 
+export class OpacityEffect implements IElementEffect {
+    readonly type: EffectType = EffectType.OPACITY;
+    readonly target: number = EffectTarget.BACKGROUND_BORDERS | EffectTarget.CONTENT;
+    readonly opacity: number;
+
+    constructor(opacity: number) {
+        this.opacity = opacity;
+    }
+}
+
 export const isTransformEffect = (effect: IElementEffect): effect is TransformEffect =>
     effect.type === EffectType.TRANSFORM;
 export const isClipEffect = (effect: IElementEffect): effect is ClipEffect => effect.type === EffectType.CLIP;
+export const isOpacityEffect = (effect: IElementEffect): effect is OpacityEffect => effect.type === EffectType.OPACITY;
diff --git a/src/render/stacking-context.ts b/src/render/stacking-context.ts
index 27787b619..5cba00bfd 100644
--- a/src/render/stacking-context.ts
+++ b/src/render/stacking-context.ts
@@ -1,7 +1,7 @@
 import {ElementContainer, FLAGS} from '../dom/element-container';
 import {contains} from '../core/bitwise';
 import {BoundCurves, calculateBorderBoxPath, calculatePaddingBoxPath} from './bound-curves';
-import {ClipEffect, EffectTarget, IElementEffect, TransformEffect} from './effects';
+import {ClipEffect, EffectTarget, IElementEffect, OpacityEffect, TransformEffect} from './effects';
 import {OVERFLOW} from '../css/property-descriptors/overflow';
 import {equalPath} from './path';
 import {DISPLAY} from '../css/property-descriptors/display';
@@ -41,6 +41,10 @@ export class ElementPaint {
         this.container = element;
         this.effects = parentStack.slice(0);
         this.curves = new BoundCurves(element);
+        if (element.styles.opacity < 1) {
+            this.effects.push(new OpacityEffect(element.styles.opacity));
+        }
+
         if (element.styles.transform !== null) {
             const offsetX = element.bounds.left + element.styles.transformOrigin[0].number;
             const offsetY = element.bounds.top + element.styles.transformOrigin[1].number;
diff --git a/tests/reftests/overflow/overflow.html b/tests/reftests/overflow/overflow.html
index 43618a56c..6a9f0e9a6 100644
--- a/tests/reftests/overflow/overflow.html
+++ b/tests/reftests/overflow/overflow.html
@@ -128,5 +128,6 @@ <h1>Overflow: hidden</h1>
 
     </script>
 </div>
+<div class="hidden">Hidden<div style="opacity: 0.5">With opacity</div></div>
 </body>
 </html>