canvas 使用 Affine,实现任意点变换(旋转,位移,缩放

矩阵入门教程及文件获取地址

http://www.seeshiontech.com/docs/page_145.html

1.首先我们创建 canvas 标签,为了方便查看效果,我们为 canvas 添加一下样式,这里图片我使用的是 1920*1080 的尺寸

<canvas id="canvas" width="1920" height="1080"></canvas>

 canvas {
            display: block;
            border: 1px solid;
            width: 480px;
            height: 270px;
            margin: 100px auto;
        }

 //不做处理 将图片绘制到画布
 let image = document.createElement("img");
        let context = canvas.getContext("2d");
        image.src = "http://static.atvideo.cc/veleap/templateDemo/2021/04/06/16/30aawseyhgae.png";
        image.onload = function () {
            context.drawImage(
                image,
                0,
                0,
            );
        }

2.引入 Affine.js 文件

<script src="./lib/Affine.js"></script>

3.使用矩阵中心点旋转缩放

 let image = document.createElement("img");
        let context = canvas.getContext("2d");
        image.src = "http://static.atvideo.cc/veleap/templateDemo/2021/04/06/16/30aawseyhgae.png";
        image.onload = function () {
            const imageWidth = image.width,
                imageHeight = image.height,
                centerPointX = imageWidth / 2,
                centerPointY = imageHeight / 2;
            let a = {
                x: centerPointX,
                y: centerPointY,
            },
                p = {
                    x: centerPointX,
                    y: centerPointY,
                },
                s = {
                    x: 0.5,
                    y: 0.5,
                },
                r = 45;

            let matrix = new Affine();
            matrix.set(a, p, s, r);
            context.setTransform(matrix.mA, matrix.mB, matrix.mC, matrix.mD, matrix.mE, matrix.mF);
            context.drawImage(
                image,
                0,
                0,
            );
        }