ant-design/components/watermark/useClips.ts

import type { WatermarkProps } from '.';

export const FontGap = 3;

function prepareCanvas(
  width: number,
  height: number,
  ratio = 1,
): [
  ctx: CanvasRenderingContext2D,
  canvas: HTMLCanvasElement,
  realWidth: number,
  realHeight: number,
] {
  const canvas = document.createElement('canvas');
  const ctx = canvas.getContext('2d')!;

  const realWidth = width * ratio;
  const realHeight = height * ratio;
  canvas.setAttribute('width', `${realWidth}px`);
  canvas.setAttribute('height', `${realHeight}px`);
  ctx.save();

  return [ctx, canvas, realWidth, realHeight];
}

/**
 * Get the clips of text content.
 * This is a lazy hook function since SSR no need this
 */
export default function useClips() {
  // Get single clips
  function getClips(
    content: NonNullable<WatermarkProps['content']> | HTMLImageElement,
    rotate: number,
    ratio: number,
    width: number,
    height: number,
    font: Required<NonNullable<WatermarkProps['font']>>,
    gapX: number,
    gapY: number,
  ): [dataURL: string, finalWidth: number, finalHeight: number] {
    // ================= Text / Image =================
    const [ctx, canvas, contentWidth, contentHeight] = prepareCanvas(width, height, ratio);

    if (content instanceof HTMLImageElement) {
      // Image
      ctx.drawImage(content, 0, 0, contentWidth, contentHeight);
    } else {
      // Text
      const { color, fontSize, fontStyle, fontWeight, fontFamily, textAlign } = font;
      const mergedFontSize = Number(fontSize) * ratio;

      ctx.font = `${fontStyle} normal ${fontWeight} ${mergedFontSize}px/${height}px ${fontFamily}`;
      ctx.fillStyle = color;
      ctx.textAlign = textAlign;
      ctx.textBaseline = 'top';
      const contents = Array.isArray(content) ? content : [content];
      contents?.forEach((item, index) => {
        ctx.fillText(item ?? '', contentWidth / 2, index * (mergedFontSize + FontGap * ratio));
      });
    }

    // ==================== Rotate ====================
    const angle = (Math.PI / 180) * Number(rotate);
    const maxSize = Math.max(width, height);
    const [rCtx, rCanvas, realMaxSize] = prepareCanvas(maxSize, maxSize, ratio);

    // Copy from `ctx` and rotate
    rCtx.translate(realMaxSize / 2, realMaxSize / 2);
    rCtx.rotate(angle);
    if (contentWidth > 0 && contentHeight > 0) {
      rCtx.drawImage(canvas, -contentWidth / 2, -contentHeight / 2);
    }

    // Get boundary of rotated text
    function getRotatePos(x: number, y: number) {
      const targetX = x * Math.cos(angle) - y * Math.sin(angle);
      const targetY = x * Math.sin(angle) + y * Math.cos(angle);
      return [targetX, targetY];
    }

    let left = 0;
    let right = 0;
    let top = 0;
    let bottom = 0;

    const halfWidth = contentWidth / 2;
    const halfHeight = contentHeight / 2;
    const points = [
      [0 - halfWidth, 0 - halfHeight],
      [0 + halfWidth, 0 - halfHeight],
      [0 + halfWidth, 0 + halfHeight],
      [0 - halfWidth, 0 + halfHeight],
    ];
    points.forEach(([x, y]) => {
      const [targetX, targetY] = getRotatePos(x, y);
      left = Math.min(left, targetX);
      right = Math.max(right, targetX);
      top = Math.min(top, targetY);
      bottom = Math.max(bottom, targetY);
    });

    const cutLeft = left + realMaxSize / 2;
    const cutTop = top + realMaxSize / 2;
    const cutWidth = right - left;
    const cutHeight = bottom - top;

    // ================ Fill Alternate ================
    const realGapX = gapX * ratio;
    const realGapY = gapY * ratio;
    const filledWidth = (cutWidth + realGapX) * 2;
    const filledHeight = cutHeight + realGapY;

    const [fCtx, fCanvas] = prepareCanvas(filledWidth, filledHeight);

    function drawImg(targetX = 0, targetY = 0) {
      fCtx.drawImage(
        rCanvas,
        cutLeft,
        cutTop,
        cutWidth,
        cutHeight,
        targetX,
        targetY,
        cutWidth,
        cutHeight,
      );
    }
    drawImg();
    drawImg(cutWidth + realGapX, -cutHeight / 2 - realGapY / 2);
    drawImg(cutWidth + realGapX, +cutHeight / 2 + realGapY / 2);

    return [fCanvas.toDataURL(), filledWidth / ratio, filledHeight / ratio];
  }

  return getClips;
}