CanvasContext.setGlobalAlpha

解釋：設(shè)置全局畫筆透明度。

方法參數(shù)

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

示例

圖片示例

代碼示例 1 

在開發(fā)者工具中打開

<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();
    }
});

代碼示例 2：同時(shí)設(shè)置多個(gè)透明度 

在開發(fā)者工具中打開

<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();
    }
});