wxapp canvas canvas

canvas

Note:

1. canvas tag The default width is 300px and the height is 225px

2. The canvas-id in the same page cannot be repeated. If you use a canvas-id that has already appeared, the canvas tag corresponding to The canvas will be hidden and no longer work properly

<!-- canvas.wxml -->
<canvas style="width: 300px; height: 200px;" canvas-id="firstCanvas"></canvas>
<!-- 当使用绝对定位时，文档流后边的canvas的显示层级高于前边的canvas-->
<canvas style="width: 400px; height: 500px;" canvas-id="secondCanvas"></canvas>
<!-- 因为canvas-id与前一个canvas重复，该canvas不会显示，并会发送一个错误事件到AppService -->
<canvas style="width: 400px; height: 500px;" canvas-id="secondCanvas" binderror="canvasIdErrorCallback"></canvas>

// canvas.js
Page({
  canvasIdErrorCallback: function (e) {
    console.error(e.detail.errMsg);
  },
  onReady: function (e) {

    //使用wx.createContext获取绘图上下文context
    var context = wx.createContext();

    context.setStrokeStyle("#00ff00");
    context.setLineWidth(5);
    context.rect(0,0,200,200);
    context.stroke()
    context.setStrokeStyle ("#ff0000") ;
    context.setLineWidth (2)
    context.moveTo(160,100)
    context.arc(100,100,60,0,2*Math.PI,true);
    context.moveTo(140,100);
    context.arc(100,100,40,0,Math.PI,false);
    context.moveTo(85,80);
    context.arc(80,80,5,0,2*Math.PI,true);
    context.moveTo(125,80);
    context.arc(120,80,5,0,2*Math.PI,true);
    context.stroke();

    //调用wx.drawCanvas，通过canvasId指定在哪张画布上绘制，通过actions指定绘制行为
    wx.drawCanvas({
      canvasId: 'firstCanvas',
      actions: context.getActions() //获取绘图动作数组
    });
  }
});

Related APIs: wx.createContext, wx.drawCanvas

Bug & Tip

1. tip: Do not use the canvas component in
scroll-view