canvas-renderer.ts

import {ElementPaint, parseStackingContexts, StackingContext} from '../stacking-context';
import {asString, Color, isTransparent} from '../../css/types/color';
import {Logger} from '../../core/logger';
import {ElementContainer} from '../../dom/element-container';
import {BORDER_STYLE} from '../../css/property-descriptors/border-style';
import {CSSParsedDeclaration} from '../../css/index';
import {TextContainer} from '../../dom/text-container';
import {Path, transformPath} from '../path';
import {BACKGROUND_CLIP} from '../../css/property-descriptors/background-clip';
import {BoundCurves, calculateBorderBoxPath, calculateContentBoxPath, calculatePaddingBoxPath} from '../bound-curves';
import {isBezierCurve} from '../bezier-curve';
import {Vector} from '../vector';
import {CSSImageType, CSSURLImage, isLinearGradient, isRadialGradient} from '../../css/types/image';
import {parsePathForBorder} from '../border';
import {Cache} from '../../core/cache-storage';
import {calculateBackgroundRendering, getBackgroundValueForIndex} from '../background';
import {isDimensionToken} from '../../css/syntax/parser';
import {TextBounds} from '../../css/layout/text';
import {fromCodePoint, toCodePoints} from 'css-line-break';
import {ImageElementContainer} from '../../dom/replaced-elements/image-element-container';
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 {contains} from '../../core/bitwise';
import {calculateGradientDirection, calculateRadius, processColorStops} from '../../css/types/functions/gradient';
import {FIFTY_PERCENT, getAbsoluteValue} from '../../css/types/length-percentage';
import {TEXT_DECORATION_LINE} from '../../css/property-descriptors/text-decoration-line';
import {FontMetrics} from '../font-metrics';
import {DISPLAY} from '../../css/property-descriptors/display';
import {Bounds} from '../../css/layout/bounds';
import {LIST_STYLE_TYPE} from '../../css/property-descriptors/list-style-type';
import {computeLineHeight} from '../../css/property-descriptors/line-height';
import {CHECKBOX, INPUT_COLOR, InputElementContainer, RADIO} from '../../dom/replaced-elements/input-element-container';
import {TEXT_ALIGN} from '../../css/property-descriptors/text-align';
import {TextareaElementContainer} from '../../dom/elements/textarea-element-container';
import {SelectElementContainer} from '../../dom/elements/select-element-container';
import {IFrameElementContainer} from '../../dom/replaced-elements/iframe-element-container';
import {TextShadow} from '../../css/property-descriptors/text-shadow';

export type RenderConfigurations = RenderOptions & {
    backgroundColor: Color | null;
};

export interface RenderOptions {
    id: string;
    scale: number;
    canvas?: HTMLCanvasElement;
    x: number;
    y: number;
    scrollX: number;
    scrollY: number;
    width: number;
    height: number;
    windowWidth: number;
    windowHeight: number;
    cache: Cache;
}

const MASK_OFFSET = 10000;

export class CanvasRenderer {
    canvas: HTMLCanvasElement;
    ctx: CanvasRenderingContext2D;
    options: RenderConfigurations;
    private readonly _activeEffects: IElementEffect[] = [];
    private readonly fontMetrics: FontMetrics;

    constructor(options: RenderConfigurations) {
        this.canvas = options.canvas ? options.canvas : document.createElement('canvas');
        this.ctx = this.canvas.getContext('2d') as CanvasRenderingContext2D;
        this.options = options;
        if (!options.canvas) {
            this.canvas.width = Math.floor(options.width * options.scale);
            this.canvas.height = Math.floor(options.height * options.scale);
            this.canvas.style.width = `${options.width}px`;
            this.canvas.style.height = `${options.height}px`;
        }
        this.fontMetrics = new FontMetrics(document);
        this.ctx.scale(this.options.scale, this.options.scale);
        this.ctx.translate(-options.x + options.scrollX, -options.y + options.scrollY);
        this.ctx.textBaseline = 'bottom';
        this._activeEffects = [];
        Logger.getInstance(options.id).debug(
            `Canvas renderer initialized (${options.width}x${options.height} at ${options.x},${options.y}) with scale ${
                options.scale
            }`
        );
    }

    applyEffects(effects: IElementEffect[], target: EffectTarget) {
        while (this._activeEffects.length) {
            this.popEffect();
        }

        effects.filter(effect => contains(effect.target, target)).forEach(effect => this.applyEffect(effect));
    }

    applyEffect(effect: IElementEffect) {
        this.ctx.save();
        if (isTransformEffect(effect)) {
            this.ctx.translate(effect.offsetX, effect.offsetY);
            this.ctx.transform(
                effect.matrix[0],
                effect.matrix[1],
                effect.matrix[2],
                effect.matrix[3],
                effect.matrix[4],
                effect.matrix[5]
            );
            this.ctx.translate(-effect.offsetX, -effect.offsetY);
        }

        if (isClipEffect(effect)) {
            this.path(effect.path);
            this.ctx.clip();
        }

        this._activeEffects.push(effect);
    }

    popEffect() {
        this._activeEffects.pop();
        this.ctx.restore();
    }

    async renderStack(stack: StackingContext) {
        const styles = stack.element.container.styles;
        if (styles.isVisible()) {
            this.ctx.globalAlpha = styles.opacity;
            await this.renderStackContent(stack);
        }
    }

    async renderNode(paint: ElementPaint) {
        if (paint.container.styles.isVisible()) {
            await this.renderNodeBackgroundAndBorders(paint);
            await this.renderNodeContent(paint);
        }
    }

    renderTextWithLetterSpacing(text: TextBounds, letterSpacing: number) {
        if (letterSpacing === 0) {
            this.ctx.fillText(text.text, text.bounds.left, text.bounds.top + text.bounds.height);
        } else {
            const letters = toCodePoints(text.text).map(i => fromCodePoint(i));
            letters.reduce((left, letter) => {
                this.ctx.fillText(letter, left, text.bounds.top + text.bounds.height);

                return left + this.ctx.measureText(letter).width;
            }, text.bounds.left);
        }
    }

    private createFontStyle(styles: CSSParsedDeclaration): string[] {
        const fontVariant = styles.fontVariant
            .filter(variant => variant === 'normal' || variant === 'small-caps')
            .join('');
        const fontFamily = styles.fontFamily.join(', ');
        const fontSize = isDimensionToken(styles.fontSize)
            ? `${styles.fontSize.number}${styles.fontSize.unit}`
            : `${styles.fontSize.number}px`;

        return [
            [styles.fontStyle, fontVariant, styles.fontWeight, fontSize, fontFamily].join(' '),
            fontFamily,
            fontSize
        ];
    }

    async renderTextNode(text: TextContainer, styles: CSSParsedDeclaration) {
        const [font, fontFamily, fontSize] = this.createFontStyle(styles);

        this.ctx.font = font;

        text.textBounds.forEach(text => {
            this.ctx.fillStyle = asString(styles.color);
            this.renderTextWithLetterSpacing(text, styles.letterSpacing);
            const textShadows: TextShadow = styles.textShadow;

            if (textShadows.length && text.text.trim().length) {
                textShadows
                    .slice(0)
                    .reverse()
                    .forEach(textShadow => {
                        this.ctx.shadowColor = asString(textShadow.color);
                        this.ctx.shadowOffsetX = textShadow.offsetX.number * this.options.scale;
                        this.ctx.shadowOffsetY = textShadow.offsetY.number * this.options.scale;
                        this.ctx.shadowBlur = textShadow.blur.number;

                        this.ctx.fillText(text.text, text.bounds.left, text.bounds.top + text.bounds.height);
                    });

                this.ctx.shadowColor = '';
                this.ctx.shadowOffsetX = 0;
                this.ctx.shadowOffsetY = 0;
                this.ctx.shadowBlur = 0;
            }

            if (styles.textDecorationLine.length) {
                this.ctx.fillStyle = asString(styles.textDecorationColor || styles.color);
                styles.textDecorationLine.forEach(textDecorationLine => {
                    switch (textDecorationLine) {
                        case TEXT_DECORATION_LINE.UNDERLINE:
                            // Draws a line at the baseline of the font
                            // TODO As some browsers display the line as more than 1px if the font-size is big,
                            // need to take that into account both in position and size
                            const {baseline} = this.fontMetrics.getMetrics(fontFamily, fontSize);
                            this.ctx.fillRect(
                                text.bounds.left,
                                Math.round(text.bounds.top + baseline),
                                text.bounds.width,
                                1
                            );

                            break;
                        case TEXT_DECORATION_LINE.OVERLINE:
                            this.ctx.fillRect(text.bounds.left, Math.round(text.bounds.top), text.bounds.width, 1);
                            break;
                        case TEXT_DECORATION_LINE.LINE_THROUGH:
                            // TODO try and find exact position for line-through
                            const {middle} = this.fontMetrics.getMetrics(fontFamily, fontSize);
                            this.ctx.fillRect(
                                text.bounds.left,
                                Math.ceil(text.bounds.top + middle),
                                text.bounds.width,
                                1
                            );
                            break;
                    }
                });
            }
        });
    }

    renderReplacedElement(
        container: ReplacedElementContainer,
        curves: BoundCurves,
        image: HTMLImageElement | HTMLCanvasElement
    ) {
        if (image && container.intrinsicWidth > 0 && container.intrinsicHeight > 0) {
            const box = contentBox(container);
            const path = calculatePaddingBoxPath(curves);
            this.path(path);
            this.ctx.save();
            this.ctx.clip();
            this.ctx.drawImage(
                image,
                0,
                0,
                container.intrinsicWidth,
                container.intrinsicHeight,
                box.left,
                box.top,
                box.width,
                box.height
            );
            this.ctx.restore();
        }
    }

    async renderNodeContent(paint: ElementPaint) {
        this.applyEffects(paint.effects, EffectTarget.CONTENT);
        const container = paint.container;
        const curves = paint.curves;
        const styles = container.styles;
        for (const child of container.textNodes) {
            await this.renderTextNode(child, styles);
        }

        if (container instanceof ImageElementContainer) {
            try {
                const image = await this.options.cache.match(container.src);
                this.renderReplacedElement(container, curves, image);
            } catch (e) {
                Logger.getInstance(this.options.id).error(`Error loading image ${container.src}`);
            }
        }

        if (container instanceof CanvasElementContainer) {
            this.renderReplacedElement(container, curves, container.canvas);
        }

        if (container instanceof SVGElementContainer) {
            try {
                const image = await this.options.cache.match(container.svg);
                this.renderReplacedElement(container, curves, image);
            } catch (e) {
                Logger.getInstance(this.options.id).error(`Error loading svg ${container.svg.substring(0, 255)}`);
            }
        }

        if (container instanceof IFrameElementContainer && container.tree) {
            const iframeRenderer = new CanvasRenderer({
                id: this.options.id,
                scale: this.options.scale,
                backgroundColor: container.backgroundColor,
                x: 0,
                y: 0,
                scrollX: 0,
                scrollY: 0,
                width: container.width,
                height: container.height,
                cache: this.options.cache,
                windowWidth: container.width,
                windowHeight: container.height
            });

            const canvas = await iframeRenderer.render(container.tree);
            if (container.width && container.height) {
                this.ctx.drawImage(
                    canvas,
                    0,
                    0,
                    container.width,
                    container.height,
                    container.bounds.left,
                    container.bounds.top,
                    container.bounds.width,
                    container.bounds.height
                );
            }
        }

        if (container instanceof InputElementContainer) {
            const size = Math.min(container.bounds.width, container.bounds.height);

            if (container.type === CHECKBOX) {
                if (container.checked) {
                    this.ctx.save();
                    this.path([
                        new Vector(container.bounds.left + size * 0.39363, container.bounds.top + size * 0.79),
                        new Vector(container.bounds.left + size * 0.16, container.bounds.top + size * 0.5549),
                        new Vector(container.bounds.left + size * 0.27347, container.bounds.top + size * 0.44071),
                        new Vector(container.bounds.left + size * 0.39694, container.bounds.top + size * 0.5649),
                        new Vector(container.bounds.left + size * 0.72983, container.bounds.top + size * 0.23),
                        new Vector(container.bounds.left + size * 0.84, container.bounds.top + size * 0.34085),
                        new Vector(container.bounds.left + size * 0.39363, container.bounds.top + size * 0.79)
                    ]);

                    this.ctx.fillStyle = asString(INPUT_COLOR);
                    this.ctx.fill();
                    this.ctx.restore();
                }
            } else if (container.type === RADIO) {
                if (container.checked) {
                    this.ctx.save();
                    this.ctx.beginPath();
                    this.ctx.arc(
                        container.bounds.left + size / 2,
                        container.bounds.top + size / 2,
                        size / 4,
                        0,
                        Math.PI * 2,
                        true
                    );
                    this.ctx.fillStyle = asString(INPUT_COLOR);
                    this.ctx.fill();
                    this.ctx.restore();
                }
            }
        }

        if (isTextInputElement(container) && container.value.length) {
            [this.ctx.font] = this.createFontStyle(styles);
            this.ctx.fillStyle = asString(styles.color);

            this.ctx.textBaseline = 'middle';
            this.ctx.textAlign = canvasTextAlign(container.styles.textAlign);

            const bounds = contentBox(container);

            let x = 0;

            switch (container.styles.textAlign) {
                case TEXT_ALIGN.CENTER:
                    x += bounds.width / 2;
                    break;
                case TEXT_ALIGN.RIGHT:
                    x += bounds.width;
                    break;
            }

            const textBounds = bounds.add(x, 0, 0, -bounds.height / 2 + 1);

            this.ctx.save();
            this.path([
                new Vector(bounds.left, bounds.top),
                new Vector(bounds.left + bounds.width, bounds.top),
                new Vector(bounds.left + bounds.width, bounds.top + bounds.height),
                new Vector(bounds.left, bounds.top + bounds.height)
            ]);

            this.ctx.clip();
            this.renderTextWithLetterSpacing(new TextBounds(container.value, textBounds), styles.letterSpacing);
            this.ctx.restore();
            this.ctx.textBaseline = 'bottom';
            this.ctx.textAlign = 'left';
        }

        if (contains(container.styles.display, DISPLAY.LIST_ITEM)) {
            if (container.styles.listStyleImage !== null) {
                const img = container.styles.listStyleImage;
                if (img.type === CSSImageType.URL) {
                    let image;
                    const url = (img as CSSURLImage).url;
                    try {
                        image = await this.options.cache.match(url);
                        this.ctx.drawImage(image, container.bounds.left - (image.width + 10), container.bounds.top);
                    } catch (e) {
                        Logger.getInstance(this.options.id).error(`Error loading list-style-image ${url}`);
                    }
                }
            } else if (paint.listValue && container.styles.listStyleType !== LIST_STYLE_TYPE.NONE) {
                [this.ctx.font] = this.createFontStyle(styles);
                this.ctx.fillStyle = asString(styles.color);

                this.ctx.textBaseline = 'middle';
                this.ctx.textAlign = 'right';
                const bounds = new Bounds(
                    container.bounds.left,
                    container.bounds.top + getAbsoluteValue(container.styles.paddingTop, container.bounds.width),
                    container.bounds.width,
                    computeLineHeight(styles.lineHeight, styles.fontSize.number) / 2 + 1
                );

                this.renderTextWithLetterSpacing(new TextBounds(paint.listValue, bounds), styles.letterSpacing);
                this.ctx.textBaseline = 'bottom';
                this.ctx.textAlign = 'left';
            }
        }
    }

    async renderStackContent(stack: StackingContext) {
        // 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);
        // 2. the child stacking contexts with negative stack levels (most negative first).
        for (const child of stack.negativeZIndex) {
            await this.renderStack(child);
        }
        // 3. For all its in-flow, non-positioned, block-level descendants in tree order:
        await this.renderNodeContent(stack.element);

        for (const child of stack.nonInlineLevel) {
            await this.renderNode(child);
        }
        // 4. All non-positioned floating descendants, in tree order. For each one of these,
        // treat the element as if it created a new stacking context, but any positioned descendants and descendants
        // which actually create a new stacking context should be considered part of the parent stacking context,
        // not this new one.
        for (const child of stack.nonPositionedFloats) {
            await this.renderStack(child);
        }
        // 5. the in-flow, inline-level, non-positioned descendants, including inline tables and inline blocks.
        for (const child of stack.nonPositionedInlineLevel) {
            await this.renderStack(child);
        }
        for (const child of stack.inlineLevel) {
            await this.renderNode(child);
        }
        // 6. All positioned, opacity or transform descendants, in tree order that fall into the following categories:
        //  All positioned descendants with 'z-index: auto' or 'z-index: 0', in tree order.
        //  For those with 'z-index: auto', treat the element as if it created a new stacking context,
        //  but any positioned descendants and descendants which actually create a new stacking context should be
        //  considered part of the parent stacking context, not this new one. For those with 'z-index: 0',
        //  treat the stacking context generated atomically.
        //
        //  All opacity descendants with opacity less than 1
        //
        //  All transform descendants with transform other than none
        for (const child of stack.zeroOrAutoZIndexOrTransformedOrOpacity) {
            await this.renderStack(child);
        }
        // 7. Stacking contexts formed by positioned descendants with z-indices greater than or equal to 1 in z-index
        // order (smallest first) then tree order.
        for (const child of stack.positiveZIndex) {
            await this.renderStack(child);
        }
    }

    mask(paths: Path[]) {
        this.ctx.beginPath();
        this.ctx.moveTo(0, 0);
        this.ctx.lineTo(this.canvas.width, 0);
        this.ctx.lineTo(this.canvas.width, this.canvas.height);
        this.ctx.lineTo(0, this.canvas.height);
        this.ctx.lineTo(0, 0);
        this.formatPath(paths.slice(0).reverse());
        this.ctx.closePath();
    }

    path(paths: Path[]) {
        this.ctx.beginPath();
        this.formatPath(paths);
        this.ctx.closePath();
    }

    formatPath(paths: Path[]) {
        paths.forEach((point, index) => {
            const start: Vector = isBezierCurve(point) ? point.start : point;
            if (index === 0) {
                this.ctx.moveTo(start.x, start.y);
            } else {
                this.ctx.lineTo(start.x, start.y);
            }

            if (isBezierCurve(point)) {
                this.ctx.bezierCurveTo(
                    point.startControl.x,
                    point.startControl.y,
                    point.endControl.x,
                    point.endControl.y,
                    point.end.x,
                    point.end.y
                );
            }
        });
    }

    renderRepeat(path: Path[], pattern: CanvasPattern | CanvasGradient, offsetX: number, offsetY: number) {
        this.path(path);
        this.ctx.fillStyle = pattern;
        this.ctx.translate(offsetX, offsetY);
        this.ctx.fill();
        this.ctx.translate(-offsetX, -offsetY);
    }

    resizeImage(image: HTMLImageElement, width: number, height: number): HTMLCanvasElement | HTMLImageElement {
        if (image.width === width && image.height === height) {
            return image;
        }

        const canvas = (this.canvas.ownerDocument as Document).createElement('canvas');
        canvas.width = width;
        canvas.height = height;
        const ctx = canvas.getContext('2d') as CanvasRenderingContext2D;
        ctx.drawImage(image, 0, 0, image.width, image.height, 0, 0, width, height);
        return canvas;
    }

    async renderBackgroundImage(container: ElementContainer) {
        let index = container.styles.backgroundImage.length - 1;
        for (const backgroundImage of container.styles.backgroundImage.slice(0).reverse()) {
            if (backgroundImage.type === CSSImageType.URL) {
                let image;
                const url = (backgroundImage as CSSURLImage).url;
                try {
                    image = await this.options.cache.match(url);
                } catch (e) {
                    Logger.getInstance(this.options.id).error(`Error loading background-image ${url}`);
                }

                if (image) {
                    const [path, x, y, width, height] = calculateBackgroundRendering(container, index, [
                        image.width,
                        image.height,
                        image.width / image.height
                    ]);
                    const pattern = this.ctx.createPattern(
                        this.resizeImage(image, width, height),
                        'repeat'
                    ) as CanvasPattern;
                    this.renderRepeat(path, pattern, x, y);
                }
            } else if (isLinearGradient(backgroundImage)) {
                const [path, x, y, width, height] = calculateBackgroundRendering(container, index, [null, null, null]);
                const [lineLength, x0, x1, y0, y1] = calculateGradientDirection(backgroundImage.angle, width, height);

                const canvas = document.createElement('canvas');
                canvas.width = width;
                canvas.height = height;
                const ctx = canvas.getContext('2d') as CanvasRenderingContext2D;
                const gradient = ctx.createLinearGradient(x0, y0, x1, y1);

                processColorStops(backgroundImage.stops, lineLength).forEach(colorStop =>
                    gradient.addColorStop(colorStop.stop, asString(colorStop.color))
                );

                ctx.fillStyle = gradient;
                ctx.fillRect(0, 0, width, height);
                if (width > 0 && height > 0) {
                    const pattern = this.ctx.createPattern(canvas, 'repeat') as CanvasPattern;
                    this.renderRepeat(path, pattern, x, y);
                }
            } else if (isRadialGradient(backgroundImage)) {
                const [path, left, top, width, height] = calculateBackgroundRendering(container, index, [
                    null,
                    null,
                    null
                ]);
                const position = backgroundImage.position.length === 0 ? [FIFTY_PERCENT] : backgroundImage.position;
                const x = getAbsoluteValue(position[0], width);
                const y = getAbsoluteValue(position[position.length - 1], height);

                const [rx, ry] = calculateRadius(backgroundImage, x, y, width, height);
                if (rx > 0 && rx > 0) {
                    const radialGradient = this.ctx.createRadialGradient(left + x, top + y, 0, left + x, top + y, rx);

                    processColorStops(backgroundImage.stops, rx * 2).forEach(colorStop =>
                        radialGradient.addColorStop(colorStop.stop, asString(colorStop.color))
                    );

                    this.path(path);
                    this.ctx.fillStyle = radialGradient;
                    if (rx !== ry) {
                        // transforms for elliptical radial gradient
                        const midX = container.bounds.left + 0.5 * container.bounds.width;
                        const midY = container.bounds.top + 0.5 * container.bounds.height;
                        const f = ry / rx;
                        const invF = 1 / f;

                        this.ctx.save();
                        this.ctx.translate(midX, midY);
                        this.ctx.transform(1, 0, 0, f, 0, 0);
                        this.ctx.translate(-midX, -midY);

                        this.ctx.fillRect(left, invF * (top - midY) + midY, width, height * invF);
                        this.ctx.restore();
                    } else {
                        this.ctx.fill();
                    }
                }
            }
            index--;
        }
    }

    async renderBorder(color: Color, side: number, curvePoints: BoundCurves) {
        this.path(parsePathForBorder(curvePoints, side));
        this.ctx.fillStyle = asString(color);
        this.ctx.fill();
    }

    async renderNodeBackgroundAndBorders(paint: ElementPaint) {
        this.applyEffects(paint.effects, EffectTarget.BACKGROUND_BORDERS);
        const styles = paint.container.styles;
        const hasBackground = !isTransparent(styles.backgroundColor) || styles.backgroundImage.length;

        const borders = [
            {style: styles.borderTopStyle, color: styles.borderTopColor},
            {style: styles.borderRightStyle, color: styles.borderRightColor},
            {style: styles.borderBottomStyle, color: styles.borderBottomColor},
            {style: styles.borderLeftStyle, color: styles.borderLeftColor}
        ];

        const backgroundPaintingArea = calculateBackgroundCurvedPaintingArea(
            getBackgroundValueForIndex(styles.backgroundClip, 0),
            paint.curves
        );

        if (hasBackground || styles.boxShadow.length) {
            this.ctx.save();
            this.path(backgroundPaintingArea);
            this.ctx.clip();

            if (!isTransparent(styles.backgroundColor)) {
                this.ctx.fillStyle = asString(styles.backgroundColor);
                this.ctx.fill();
            }

            await this.renderBackgroundImage(paint.container);

            this.ctx.restore();

            styles.boxShadow
                .slice(0)
                .reverse()
                .forEach(shadow => {
                    this.ctx.save();
                    const borderBoxArea = calculateBorderBoxPath(paint.curves);
                    const maskOffset = shadow.inset ? 0 : MASK_OFFSET;
                    const shadowPaintingArea = transformPath(
                        borderBoxArea,
                        -maskOffset + (shadow.inset ? 1 : -1) * shadow.spread.number,
                        (shadow.inset ? 1 : -1) * shadow.spread.number,
                        shadow.spread.number * (shadow.inset ? -2 : 2),
                        shadow.spread.number * (shadow.inset ? -2 : 2)
                    );

                    if (shadow.inset) {
                        this.path(borderBoxArea);
                        this.ctx.clip();
                        this.mask(shadowPaintingArea);
                    } else {
                        this.mask(borderBoxArea);
                        this.ctx.clip();
                        this.path(shadowPaintingArea);
                    }

                    this.ctx.shadowOffsetX = shadow.offsetX.number + maskOffset;
                    this.ctx.shadowOffsetY = shadow.offsetY.number;
                    this.ctx.shadowColor = asString(shadow.color);
                    this.ctx.shadowBlur = shadow.blur.number;
                    this.ctx.fillStyle = shadow.inset ? asString(shadow.color) : 'rgba(0,0,0,1)';

                    this.ctx.fill();
                    this.ctx.restore();
                });
        }

        let side = 0;
        for (const border of borders) {
            if (border.style !== BORDER_STYLE.NONE && !isTransparent(border.color)) {
                await this.renderBorder(border.color, side, paint.curves);
            }
            side++;
        }
    }

    async render(element: ElementContainer): Promise<HTMLCanvasElement> {
        if (this.options.backgroundColor) {
            this.ctx.fillStyle = asString(this.options.backgroundColor);
            this.ctx.fillRect(
                this.options.x - this.options.scrollX,
                this.options.y - this.options.scrollY,
                this.options.width,
                this.options.height
            );
        }

        const stack = parseStackingContexts(element);

        await this.renderStack(stack);
        this.applyEffects([], EffectTarget.BACKGROUND_BORDERS);
        return this.canvas;
    }
}

const isTextInputElement = (
    container: ElementContainer
): container is InputElementContainer | TextareaElementContainer | SelectElementContainer => {
    if (container instanceof TextareaElementContainer) {
        return true;
    } else if (container instanceof SelectElementContainer) {
        return true;
    } else if (container instanceof InputElementContainer && container.type !== RADIO && container.type !== CHECKBOX) {
        return true;
    }
    return false;
};

const calculateBackgroundCurvedPaintingArea = (clip: BACKGROUND_CLIP, curves: BoundCurves): Path[] => {
    switch (clip) {
        case BACKGROUND_CLIP.BORDER_BOX:
            return calculateBorderBoxPath(curves);
        case BACKGROUND_CLIP.CONTENT_BOX:
            return calculateContentBoxPath(curves);
        case BACKGROUND_CLIP.PADDING_BOX:
        default:
            return calculatePaddingBoxPath(curves);
    }
};

const canvasTextAlign = (textAlign: TEXT_ALIGN): CanvasTextAlign => {
    switch (textAlign) {
        case TEXT_ALIGN.CENTER:
            return 'center';
        case TEXT_ALIGN.RIGHT:
            return 'right';
        case TEXT_ALIGN.LEFT:
        default:
            return 'left';
    }
};