vue 创建canvas画板制作图片和文字，支持文字自动换行

落日映苍穹つ 2023-03-12 07:13 35阅读 0赞

**canvas文档：https://www.runoob.com/jsref/dom-obj-canvas.html**

创建画板、图片、文字、自动换行都是分开方法，可以灵活调用  
里面有两个小demo，演示调用方法  
其实简单修改也可以不需要依靠vue

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
    </head>
    <style>
        img { 
            width: 100%;
            height: 100%;
        }
    </style>
    <body style="background-color: blue">
    <div id="app">
        
        <canvas style="display: none" id="myCanvas" width=""></canvas>
        
        <img :src="img_src" alt="">
    </div>
    </body>
    </html>
    <script src="https://cdn.jsdelivr.net/npm/vue"></script>
    <script>
        let v = new Vue({ 
            el: '#app',
            data: { 
                img_src: '',
                ctx: '',
                myCanvas: '',
            },
            methods: { 
                makePlan() {  // demo1
                    let row = 15; // 行数会影响页面的长度 签字预留400 顶部预留100
                    this.makeCanvas(400, 500 + 20 * row); // 签字预留400 上面文字 100+20*行数
                    //文本
                    this.makeText('标题', 200, 40, 'center', '#000', '20px Arial')
                    this.makeLine(20, 60, 380, 60);
                    this.makeText('任务', 100, 100, 'center', '#000', '16px Arial')
                    this.makeText('单位', 300, 100, 'center', '#000', '16px Arial')
                    let i = 0;
                    for (i = 0; i < row; i++) { 
                        this.makeText('2020-02-13-2020-03-13', 100, 120 + 20 * i, 'center')
                        this.makeText('90次', 300, 120 + 20 * i, 'center')
                    }
                    this.makeLine(20, 120 + 20 * i, 380, 120 + 20 * i);
                    let img = 'https://csdnimg.cn/public/common/toolbar/images/eduwxfix.png'
                    this.makeImage(img, 20, 400, 360); // 创建图片
                    this.imagePut();
                },
                makeFloat(text) {  // demo2
                    // 超长画布来计算文字预计的高度
                    this.makeCanvas(400, 10000);
                    let y = this.autoRow(text, 20, 0, 360, 20, '16px Arial')  // 计算文字的总高度
                    this.makeCanvas(400, 500 + y); // 签字预留400 上面文字 100+20*行数
                    //文本
                    this.makeText('考核任务', 200, 40, 'center', '#000', '20px Arial')
                    this.makeLine(20, 60, 380, 60);
                    y = this.autoRow(text, 20, 90, 360, 20, '16px Arial')
                    this.makeLine(20, 20 + y, 380, 20 + y);
                    this.imagePut();
                },
                makeImage(url, x, y, width) { 
                    let image = new Image();
                    image.setAttribute('crossOrigin', 'anonymous')
                    image.src = url;
                    image.onload = () => { 
                        this.ctx.drawImage(image, x, y, width, image.height * width / image.height);
                    }
                },
                imagePut(type) {  // 输出图像
                    // 因为需要渲染图像才能导出，暂时没啥办法，几计时刷新了，有大牛好办法可以留言
                    let i = 0;
                    let t = setInterval(() => { 
                        i++;
                        this.img_src = this.ctx.canvas.toDataURL(type);
                        if (i > 100) { 
                            clearInterval(t)
                        }
                    }, 100);
                },
                makeCanvas(width, height) {  // 初始化画板
                    this.myCanvas = document.getElementById('myCanvas');  // 画板id
                    this.myCanvas.width = width;  //尺寸
                    this.myCanvas.height = height;
                    this.ctx = this.myCanvas.getContext('2d');
                    this.ctx.fillStyle = '#ffffff';
                    this.ctx.fillStyle = '#fff';
                    this.ctx.fillRect(0, 0, this.myCanvas.width, this.myCanvas.height);
                },
                makeText(text, x, y, align, color, font) {  //文字
                    this.ctx.font = !font ? '14px Arial' : font;
                    this.ctx.fillStyle = !color ? '#4a4a4a' : color;
                    this.ctx.textAlign = !align ? 'left' : align;
                    this.ctx.fillText(text, x, y);
                },
                makeLine(start_x, start_y, end_x, end_y, cap,) {  // 线条
                    this.ctx.beginPath();
                    this.ctx.lineCap = !cap ? "round" : cap;
                    this.ctx.moveTo(start_x, start_y);
                    this.ctx.lineTo(end_x, end_y);
                    this.ctx.stroke();
                },
                /** * 自动换行 * @param text * @param x * @param y * @param maxWidth 最大宽度 * @param lineHeight 行高 */
                autoRow(text, x, y, maxWidth, lineHeight, font) { 
                    let arrText = text.split('');
                    let line = '';
                    this.ctx.font = !font ? '14px Arial' : font;
                    for (let n = 0; n < arrText.length; n++) { 
                        let testLine = line + arrText[n];
                        let metrics = this.ctx.measureText(testLine);
                        let testWidth = metrics.width;
                        if (testWidth > maxWidth && n > 0) { 
                            this.makeText(line, x, y)
                            line = arrText[n];
                            y += lineHeight;
                        } else { 
                            line = testLine;
                        }
                    }
                    this.makeText(line, x, y);
                    return y;
                }
            },
            created() { 
                this.makePlan('');
            }
        })
    
    </script>