feat: add support for data-html2canvas-debug property for debugging (#2658)

src/core/debugger.ts

@@ -0,0 +1,29 @@
+const elementDebuggerAttribute = 'data-html2canvas-debug';
+export const enum DebuggerType {
+    NONE,
+    ALL,
+    CLONE,
+    PARSE,
+    RENDER
+}
+
+const getElementDebugType = (element: Element): DebuggerType => {
+    const attribute = element.getAttribute(elementDebuggerAttribute);
+    switch (attribute) {
+        case 'all':
+            return DebuggerType.ALL;
+        case 'clone':
+            return DebuggerType.CLONE;
+        case 'parse':
+            return DebuggerType.PARSE;
+        case 'render':
+            return DebuggerType.RENDER;
+        default:
+            return DebuggerType.NONE;
+    }
+};
+
+export const isDebugging = (element: Element, type: Omit<DebuggerType, DebuggerType.NONE>): boolean => {
+    const elementType = getElementDebugType(element);
+    return elementType === DebuggerType.ALL || type === elementType;
+};

src/dom/document-cloner.ts

@@ -20,6 +20,7 @@ import {LIST_STYLE_TYPE, listStyleType} from '../css/property-descriptors/list-s
 import {CSSParsedCounterDeclaration, CSSParsedPseudoDeclaration} from '../css/index';
 import {getQuote} from '../css/property-descriptors/quotes';
 import {Context} from '../core/context';
+import {DebuggerType, isDebugging} from '../core/debugger';
 
 export interface CloneOptions {
     ignoreElements?: (element: Element) => boolean;
@@ -136,6 +137,9 @@ export class DocumentCloner {
     }
 
     createElementClone<T extends HTMLElement | SVGElement>(node: T): HTMLElement | SVGElement {
+        if (isDebugging(node, DebuggerType.CLONE)) {
+            debugger;
+        }
         if (isCanvasElement(node)) {
             return this.createCanvasClone(node);
         }

src/dom/element-container.ts

@@ -3,24 +3,27 @@ import {TextContainer} from './text-container';
 import {Bounds, parseBounds} from '../css/layout/bounds';
 import {isHTMLElementNode} from './node-parser';
 import {Context} from '../core/context';
+import {DebuggerType, isDebugging} from '../core/debugger';
 
 export const enum FLAGS {
     CREATES_STACKING_CONTEXT = 1 << 1,
     CREATES_REAL_STACKING_CONTEXT = 1 << 2,
-    IS_LIST_OWNER = 1 << 3
+    IS_LIST_OWNER = 1 << 3,
+    DEBUG_RENDER = 1 << 4
 }
 
 export class ElementContainer {
     readonly styles: CSSParsedDeclaration;
-    readonly textNodes: TextContainer[];
-    readonly elements: ElementContainer[];
+    readonly textNodes: TextContainer[] = [];
+    readonly elements: ElementContainer[] = [];
     bounds: Bounds;
-    flags: number;
+    flags = 0;
 
     constructor(protected readonly context: Context, element: Element) {
+        if (isDebugging(element, DebuggerType.PARSE)) {
+            debugger;
+        }
         this.styles = new CSSParsedDeclaration(context, window.getComputedStyle(element, null));
-        this.textNodes = [];
-        this.elements = [];
 
         if (isHTMLElementNode(element)) {
             if (this.styles.animationDuration.some((duration) => duration > 0)) {
@@ -37,6 +40,9 @@ export class ElementContainer {
         }
 
         this.bounds = parseBounds(this.context, element);
-        this.flags = 0;
+
+        if (isDebugging(element, DebuggerType.RENDER)) {
+            this.flags |= FLAGS.DEBUG_RENDER;
+        }
     }
 }

src/render/canvas/canvas-renderer.ts

@@ -1,6 +1,6 @@
 import {ElementPaint, parseStackingContexts, StackingContext} from '../stacking-context';
 import {asString, Color, isTransparent} from '../../css/types/color';
-import {ElementContainer} from '../../dom/element-container';
+import {ElementContainer, FLAGS} from '../../dom/element-container';
 import {BORDER_STYLE} from '../../css/property-descriptors/border-style';
 import {CSSParsedDeclaration} from '../../css/index';
 import {TextContainer} from '../../dom/text-container';
@@ -135,6 +135,10 @@ export class CanvasRenderer extends Renderer {
     }
 
     async renderNode(paint: ElementPaint): Promise<void> {
+        if (contains(paint.container.flags, FLAGS.DEBUG_RENDER)) {
+            debugger;
+        }
+
         if (paint.container.styles.isVisible()) {
             await this.renderNodeBackgroundAndBorders(paint);
             await this.renderNodeContent(paint);
@@ -468,6 +472,9 @@ export class CanvasRenderer extends Renderer {
     }
 
     async renderStackContent(stack: StackingContext): Promise<void> {
+        if (contains(stack.element.container.flags, FLAGS.DEBUG_RENDER)) {
+            debugger;
+        }
         // https://www.w3.org/TR/css-position-3/#painting-order
         // 1. the background and borders of the element forming the stacking context.
         await this.renderNodeBackgroundAndBorders(stack.element);