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Mobile Platform as a Service:Canvas

Last Updated:Jul 29, 2022

API

Attribute name
Type
Default value
Description
id
String

-

Unique identifier of a component
style
String

-

Declare the style of the canvas.

class
String

-

Stycle class

width
String
-

Canvas width

height
String
-

Canvas height

disable-scroll
Boolean
false
Disable screen scrolling and pull-to-refresh.
onTap
EventHandle

-

Click
onTouchStart
EventHandle

-

Touch action starts
onTouchMove
EventHandle

-

Moves after touching
onTouchEnd
EventHandle

-

Touch action ends
onTouchCancel
EventHandle

-

The touch action is interrupted such as by incoming call and pop-up dialog.
onLongTap
EventHandle

-

Triggered after a long press of 500 ms. When a long press event is triggered, moving will not trigger the screen scrolling.

Important:

  • Canvas has a width of 300 px and a height of 225 px by default.

  • IDs on the same page cannot be duplicate.

  • If you require a more detailed display under high DPR, you need to first zoom in canvas with its attribute settings and then zoom out with styles. For example:

<!-- getSystemInfoSync().pixelRatio === 2 -->
<canvas width="200" height="200" style="width:100px;height:100px;"/>

Legend

image | center

Code sample

<canvas
  id="canvas"
  class="canvas"
  onTouchStart="log"
  onTouchMove="log"
  onTouchEnd="log"
/>
Page({
  onReady() {
    this.point = {
      x: Math.random() * 295,
      y: Math.random() * 295,
      dx: Math.random() * 5,
      dy: Math.random() * 5,
      r: Math.round(Math.random() * 255 | 0),
      g: Math.round(Math.random() * 255 | 0),
          b: Math.round(Math.random() * 255 | 0),
    };

    this.interval = setInterval(this.draw, 17);
  },

  draw() {
    var ctx = my.createCanvasContext('canvas');
    ctx.setFillStyle('#FFF');
    ctx.fillRect(0, 0, 305, 305);

    ctx.beginPath();
    ctx.arc(this.point.x, this.point.y, 10, 0, 2 * Math.PI);
    ctx.setFillStyle("rgb(" + this.point.r + ", " + this.point.g + ", " + this.point.b + ")");
    ctx.fill();
    ctx.draw();

    this.point.x += this.point.dx;
    this.point.y += this.point.dy;
    if (this.point.x <= 5 || this.point.x >= 295) {
      this.point.dx = -this.point.dx;
      this.point.r = Math.round(Math.random() * 255 | 0);
      this.point.g = Math.round(Math.random() * 255 | 0);
      this.point.b = Math.round(Math.random() * 255 | 0);
    }

    if (this.point.y <= 5 || this.point.y >= 295) {
      this.point.dy = -this.point.dy;
      this.point.r = Math.round(Math.random() * 255 | 0);
      this.point.g = Math.round(Math.random() * 255 | 0);
      this.point.b = Math.round(Math.random() * 255 | 0);
    }
  },
  drawBall() {

  },
  log(e) {
    if (e.touches && e.touches[0]) {
      console.log(e.type, e.touches[0].x, e.touches[0].y);
    } else {
      console.log(e.type);
    }
  },
  onUnload() {
    clearInterval(this.interval)
  }
})