CanvasContext.setGlobalAlpha

解释：设置全局画笔透明度。

方法参数

Number alpha ：透明度取值范围： 0~1 ， 0 表示完全透明， 1 表示完全不透明。

示例

图片示例

代码示例 1 

在开发者工具中打开

<canvas canvas-id="myCanvas" class="myCanvas" />

Page({
    onLoad() {
        const canvasContext = swan.createCanvasContext('myCanvas');
        canvasContext.setFillStyle('red');
        canvasContext.fillRect(10, 10, 150, 100);
        canvasContext.setGlobalAlpha(0.2);
        canvasContext.setFillStyle('blue');
        canvasContext.fillRect(50, 50, 150, 100);
        canvasContext.setFillStyle('yellow');
        canvasContext.fillRect(100, 100, 150, 100);
        canvasContext.draw();
    }
});

代码示例 2：同时设置多个透明度 

在开发者工具中打开

<canvas canvas-id="myCanvas" class="myCanvas" />

Page({
    onLoad() {
        const canvasContext = swan.createCanvasContext('myCanvas');
        canvasContext.setGlobalAlpha(0.2);
        canvasContext.setFillStyle('red');
        canvasContext.fillRect(10, 10, 150, 100);   
        canvasContext.setGlobalAlpha(1);
        canvasContext.setFillStyle('blue');
        canvasContext.fillRect(50, 50, 150, 100); 
        canvasContext.setGlobalAlpha(0.1); 
        canvasContext.setFillStyle('yellow');
        canvasContext.fillRect(100, 100, 150, 100);
        canvasContext.draw();
    }
});