目录

变形处理

 

概述

Canvas API中提供的变形方法主要有:

CanvasRenderingContext2D.scale(x, y)
CanvasRenderingContext2D.rotate(angle)
CanvasRenderingContext2D.translate(x, y)
CanvasRenderingContext2D.transform(a, b, c, d, e, f)
CanvasRenderingContext2D.setTransform(a, b, c, d, e, f)

代码示例

绘制图片一节示例中我们使用GridFunny提供的clone方法实现类似缩放的效果,下面使用scale方法再次实现缩放:

// 分别为GridFunny添加scale、rotate、translate、transform方法
var grid = new GridFunny({
    gridColor: "green",
    canvasClassName: "transform-canvas",
    nextDraw: function() {
        var context = this.context,
            x = this.pixelX + 50,
            y = this.pixelY + 10,
            w = 240,
            h = 50;
        context.fillStyle = '#ccc';
        context.strokeStyle = 'red';
        context.font = '30px Arial';
        context.fillRect(x, y, w, h);
        context.strokeText("transform canvas", x + 5, 85);
    }
});
grid.start();
// scale
grid.scale({
    width: 300,
    height: 300
}, function(canvas) {
    canvas.className = grid.settings.canvasClassName;
    grid.settings.container.appendChild(canvas);
});
// rotate
grid.rotate({
    angle: 30 * Math.PI / 180
}, function(canvas) {
    canvas.className = grid.settings.canvasClassName;
    grid.settings.container.appendChild(canvas);
});
// translate
grid.translate({
    x: 120,
    y: 50
}, function(canvas) {
    canvas.className = grid.settings.canvasClassName;
    grid.settings.container.appendChild(canvas);
});
// transform
grid.transform({
    a: 0.5,
    b: 0.4,
    c: -0.2,
    d: 1.2,
    e: 200,
    f: 0
}, function(canvas) {
    canvas.className = grid.settings.canvasClassName;
    grid.settings.container.appendChild(canvas);
});

rotate、translate、transform方法会对canvas进行不同程度的选择,如果是原始尺寸操作的话,有部分不能完全显示,这时需要配合scale对原始canvas进行缩放,以便显示全图。

代码的执行效果如下: