WeChat applet API coordinates (Canvas coordinate system)

Canvas coordinate system

canvas is in a two-dimensional grid.

The coordinates of the upper left corner are (0, 0).

In the previous chapter, we used this method fillRect(0, 0, 150, 75).

It means: starting from the upper left corner (0, 0), draw a 150 x 75px rectangle.

Coordinate system example:

We can add some events to <canvas/> to observe its coordinate system

<canvas canvas-id="myCanvas"
  style="margin: 5px; border:1px solid #d3d3d3;"
  bindtouchstart="start"
  bindtouchmove="move"
  bindtouchend="end"/>

<view hidden="{{hidden}}">
  Coordinates: ({{x}}, {{y}})
</view>

Page({
  data: {
    x: 0,
    y: 0,
    hidden: true
  },
  start: function(e) {
    this.setData({
      hidden: false,
      x: e.touches[0].x,
      y: e.touches[0].y
    })
  },
  move: function(e) {
    this.setData({
      x: e.touches[0].x,
      y: e.touches[0].y
    })
  },
  end: function(e) {
    this.setData({
      hidden: true
    })
  }
})

When you put your finger on the canvas, the coordinates of the touch point will be displayed below: