Canvas 转 PDF——使用 JavaScript 将 HTML5 Canvas 导出为 PDF

使用 JavaScript 将任意 HTML5 Canvas 内容导出为 PDF 文档。此示例展示如何使用 jsPDF 将 Konva 舞台转换为可下载的 PDF 文件，并支持高质量渲染和可选中的文本。

此方法包含四个步骤：生成 Canvas 内容，将 Canvas 导出为图像，将该图像插入 PDF 文档，然后保存。要获得最佳结果，请注意以下两点：

高质量导出： 将 Canvas 转换为图像时，请使用 pixelRatio 属性。有关详细信息，请参阅高质量导出指南。

PDF 中的可选中文本： 虽然 Canvas 会作为图像添加，但可以手动在其下方的 PDF 图层中插入文本节点。这些文本不可见（它们位于图像后方），但仍可选择和搜索。PDF 的文本渲染方式不同于 Konva，因此复杂样式可能需要调整。

操作说明：查看下方 Canvas，然后单击按钮将其保存为 PDF。

Vanilla
React
Vue

import Konva from 'konva';
import { jsPDF } from 'jspdf';

// Create a button for PDF export
const saveButton = document.createElement('button');
saveButton.textContent = 'Save as PDF';
saveButton.style.position = 'absolute';
saveButton.style.top = '5px';
saveButton.style.left = '5px';
document.body.appendChild(saveButton);

// Create a stage
const width = window.innerWidth;
const height = window.innerHeight;

const stage = new Konva.Stage({
  container: 'container',
  width: width,
  height: height,
});

const layer = new Konva.Layer();
stage.add(layer);

// Add background
const back = new Konva.Rect({
  width: stage.width(),
  height: stage.height(),
  fill: 'rgba(200, 200, 200)',
});
layer.add(back);

// Add text with blur effect
const text = new Konva.Text({
  text: 'This is the Darth Vader',
  x: 15,
  y: 40,
  rotation: -10,
  filters: [Konva.Filters.Blur],
  blurRadius: 4,
  fontSize: 18,
});
text.cache();
layer.add(text);

// Add arrow
const arrow = new Konva.Arrow({
  points: [70, 50, 100, 80, 150, 100, 190, 100],
  tension: 0.5,
  stroke: 'black',
  fill: 'black',
});
layer.add(arrow);

// Add image
const imageUrl = 'https://konvajs.org/assets/darth-vader.jpg';
Konva.Image.fromURL(
  imageUrl,
  function (darthNode) {
    darthNode.setAttrs({
      x: 200,
      y: 50,
      scaleX: 0.5,
      scaleY: 0.5,
    });
    layer.add(darthNode);
  },
  function () {
    console.error('Failed to load image');
  }
);

// Handle PDF export
saveButton.addEventListener('click', function () {
  const pdf = new jsPDF({
    orientation: 'landscape',
    unit: 'px',
    format: [stage.width(), stage.height()],
    hotfixes: ['px_scaling'],
  });
  pdf.setTextColor('#000000');

  // First add texts
  stage.find('Text').forEach((text) => {
    const size = text.fontSize() * 0.75; // convert pixels to points
    pdf.setFontSize(size);
    pdf.text(text.text(), text.x(), text.y(), {
      baseline: 'top',
      angle: -text.getAbsoluteRotation(),
    });
  });

  // Then put image on top of texts (so texts are not visible)
  pdf.addImage(
    stage.toDataURL({ pixelRatio: 2 }),
    0,
    0,
    stage.width(),
    stage.height()
  );

  pdf.save('canvas.pdf');
});

import Konva from 'konva';
import { useEffect, useRef } from 'react';
import { Stage, Layer, Rect, Text, Arrow, Image } from 'react-konva';
import useImage from 'use-image';
import { jsPDF } from 'jspdf';

const App = () => {
  const stageRef = useRef(null);
  const textRef = useRef(null);
  const [darthVaderImage] = useImage('https://konvajs.org/assets/darth-vader.jpg', 'anonymous');
  const width = window.innerWidth;
  const height = window.innerHeight;

  useEffect(() => {
    textRef.current?.cache();
  }, []);
  
  // Handle PDF export
  const handleExport = () => {
    if (stageRef.current) {
      const stage = stageRef.current;
      const pdf = new jsPDF({
        orientation: 'landscape',
        unit: 'px',
        format: [width, height],
        hotfixes: ['px_scaling'],
      });
      pdf.setTextColor('#000000');
      
      // First add texts
      stage.find('Text').forEach((text) => {
        const size = text.fontSize() * 0.75; // convert pixels to points
        pdf.setFontSize(size);
        pdf.text(text.text(), text.x(), text.y(), {
          baseline: 'top',
          angle: -text.getAbsoluteRotation(),
        });
      });

      // Then put image on top of texts (so texts are not visible)
      pdf.addImage(
        stage.toDataURL({ pixelRatio: 2 }),
        0,
        0,
        width,
        height
      );

      pdf.save('canvas.pdf');
    } else {
      console.error('Stage is not available');
    }
  };
  
  return (
    <div style={{ position: 'relative' }}>
      <button 
        style={{ position: 'absolute', top: '5px', left: '5px', zIndex: 10 }}
        onClick={handleExport}
      >
        Save as PDF
      </button>
      
      <Stage width={width} height={height} ref={stageRef}>
        <Layer>
          <Rect
            width={width}
            height={height}
            fill="rgba(200, 200, 200)"
          />
          
          <Text
            ref={textRef}
            text="This is the Darth Vader"
            x={15}
            y={40}
            rotation={-10}
            fontSize={18}
            filters={[Konva.Filters.Blur]}
            blurRadius={4}
          />
          
          <Arrow
            points={[70, 50, 100, 80, 150, 100, 190, 100]}
            tension={0.5}
            stroke="black"
            fill="black"
          />
          
          {darthVaderImage && (
            <Image
              image={darthVaderImage}
              x={200}
              y={50}
              scaleX={0.5}
              scaleY={0.5}
            />
          )}
        </Layer>
      </Stage>
    </div>
  );
};

export default App;

<template>
  <div style="position: relative">
    <button 
      style="position: absolute; top: 5px; left: 5px; z-index: 10"
      @click="handleExport"
    >
      Save as PDF
    </button>
    
    <v-stage ref="stageRef" :config="stageConfig">
      <v-layer>
        <v-rect :config="backgroundConfig" />
        
        <v-text ref="textRef" :config="textConfig" />
        
        <v-arrow :config="arrowConfig" />
        
        <v-image 
          v-if="darthVaderImage"
          :config="imageConfig" 
        />
      </v-layer>
    </v-stage>
  </div>
</template>

<script setup>
import { ref, onMounted, computed } from 'vue';
import Konva from 'konva';
import { useImage } from 'vue-konva';
import { jsPDF } from 'jspdf';

const stageRef = ref(null);
const textRef = ref(null);
const [darthVaderImage] = useImage('https://konvajs.org/assets/darth-vader.jpg', 'anonymous');
const width = window.innerWidth;
const height = window.innerHeight;

// Stage configuration
const stageConfig = {
  width,
  height
};

// Background configuration
const backgroundConfig = {
  width,
  height,
  fill: 'rgba(200, 200, 200)'
};

// Text configuration
const textConfig = {
  text: 'This is the Darth Vader',
  x: 15,
  y: 40,
  rotation: -10,
  fontSize: 18,
  filters: [Konva.Filters.Blur],
  blurRadius: 4
};

// Arrow configuration
const arrowConfig = {
  points: [70, 50, 100, 80, 150, 100, 190, 100],
  tension: 0.5,
  stroke: 'black',
  fill: 'black'
};

// Image configuration
const imageConfig = computed(() => ({
  image: darthVaderImage.value,
  x: 200,
  y: 50,
  scaleX: 0.5,
  scaleY: 0.5
}));

onMounted(() => {
  // Cache text for blur filter to work
  if (textRef.value) {
    textRef.value.getNode().cache();
  }
});

// Handle PDF export
const handleExport = () => {
  if (stageRef.value) {
    const stage = stageRef.value.getNode();
    const pdf = new jsPDF({
      orientation: 'landscape',
      unit: 'px',
      format: [width, height],
      hotfixes: ['px_scaling'],
    });
    pdf.setTextColor('#000000');
    
    // First add texts
    stage.find('Text').forEach((text) => {
      const size = text.fontSize() * 0.75; // convert pixels to points
      pdf.setFontSize(size);
      pdf.text(text.text(), text.x(), text.y(), {
        baseline: 'top',
        angle: -text.getAbsoluteRotation(),
      });
    });

    // Then put image on top of texts (so texts are not visible)
    pdf.addImage(
      stage.toDataURL({ pixelRatio: 2 }),
      0,
      0,
      width,
      height
    );

    pdf.save('canvas.pdf');
  } else {
    console.error('Stage is not available');
  }
};
</script> 

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上述方法会将光栅图像放入 RGB 文档。商业印刷通常要求 CMYK 分色、符合 PDF/X 标准、出血和裁切标记，但浏览器 Canvas 不提供这些功能。这需要在浏览器外执行渲染步骤。 Polotno 是一款使用 Konva 构建的商业设计编辑器 SDK，它涵盖编辑器及其导出流程。

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