HTML5 Canvas笔记——图像合成

作者: 没昔 | 来源:发表于2020-05-20 00:02 被阅读0次

编程展示各种图像的合成效果，效果的名称

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>图像合成</title>
    <style>
        #canvas {
            border: 1px solid cornflowerblue;
            position: absolute;
            left: 150px;
            top: 10px;
            background: #eeeeee;
            border: thin solid #aaaaaa;
            cursor: pointer;
            -webkit-box-shadow: rgba(200, 200, 255, 0.9) 5px 5px 10px;
            -moz-box-shadow: rgba(200, 200, 255, 0.9) 5px 5px 10px;
            box-shadow: rgba(200, 200, 255, 0.9) 5px 5px 10px;
        }
    </style>
</head>
<body>
<select size="11" id="compositingSelect">
    <option value="source-atop">目标图顶部显源图</option>
    <option value='source-in'>目标图中显源图</option>
    <option value='source-out'>目标图外显源图</option>
    <option value='source-over'>目标图上显源图</option>
    <option value='destination-atop'>源图顶部显目标图</option>
    <option value='destination-in'>源图中显目标图</option>
    <option value='destination-out'>源图外显目标图</option>
    <option value='destination-over'>源图上显目标图</option>
    <option value='lighter'>源图+目标图</option>
    <option value='copy'>只显示源图</option>
    <option value='xor'>异或组合</option>
</select>
<canvas id="canvas" width="600" height="420">Canvas not supports</canvas>
</body>
<script>
    'use strict';
    let context = document.getElementById('canvas').getContext('2d'),
        selectElement = document.getElementById('compositingSelect');
    /**
     * 绘制文字
     */
    let drawText = () => {
        context.save();

        context.shadowColor = 'rgba(100, 100, 150, 0.8)';
        context.shadowOffsetX = 5;
        context.shadowOffsetY = 5;
        context.shadowBlur = 10;

        context.fillStyle = 'cornflowerblue';
        context.fillText('HTML', 20, 250);

        context.strokeStyle = 'yellow';
        context.strokeText('HTML', 20, 250);


        context.restore();
    };

    //Event handlers……

    let windowToCanvas = (canvas, x, y) => {
        let bbox = canvas.getBoundingClientRect();
        return {
          x:x-bbox.left*(canvas.width/bbox.width),
          y:y-bbox.top*(canvas.height/bbox.height)
        };

    };

    context.canvas.onmousemove=e=>{
        let loc = windowToCanvas(context.canvas,e.clientX,e.clientY);
        context.clearRect(0,0,context.canvas.width,context.canvas.height);
        drawText();

        context.save();

        //设置选项即为全局合成属性
        context.globalCompositeOperation=selectElement.value;
        context.beginPath();
        context.arc(loc.x,loc.y,100,0,Math.PI*2,false);
        context.fillStyle='orange';
        context.stroke();
        context.fill();

        context.restore();
    }

    //Init……

    selectElement.selectedIndex=3;
    context.lineWidth=0.5;
    context.font='128pt Comic-sans';
    drawText();
</script>
</html>

效果如图：