微信小程序使用canvas的画图操作示例

时间:2019-01-18
这篇文章主要介绍了微信小程序使用canvas的画图操作,结合实例形式较为详细的分析了微信小城序基于canvas的画图操作相关实现技巧与操作注意事项,需要的朋友可以参考下

本文实例讲述了微信小程序使用canvas的画图操作。分享给大家供大家参考,具体如下:

基础写起来太没动力了,也写得乱七八糟的,还是直接解决一些小问题比较方便,代码的方方面面的细节都会详尽的解释一下。

1、下面介绍一下canvas的画图,我这个简单一点,画一个带图文的背景图,图片可以从后台获取也可以选择本地的。canvas画图首先要在wxml里面新建一个<canvas>标签,一定要写上canvas-id='canvas的id',这是必须条件,如下面代码:

<canvas canvas-id='canvas' style='width:{{windowW}}px;height:{{windowH}}px'></canvas>
<button bindtap='chooseImage'>相册</button>

2、上面canvas的宽高都是js控制的,使用?wx.getSystemInfo获取屏幕的可见宽高。代码如下:

wx.getSystemInfo({
   success: function (res) {
    that.setData({
     windowW: res.windowWidth,
     windowH: res.windowHeight
    })
   },
})

相当的详细,有没有!!!

3、重点注意一下:在微信小程序的canvas画图中如果使用了网络图片,一定要先把这张图片读取下载下来(可使用wx.downloadFile),存为网络格式的图片!!!

上面这个操作是避免网络状况不好的时候canvas画图完成了背景图片确显示不出来的情况,同时,这个图片所在的域名必须在微信公众平台配置一下,代码如下:

wx.downloadFile({
   url: '图片路径',
   success: function (res) {
    that.setData({
     canvasimgbg: res.tempFilePath
    })
   }
})

4、 我上面wxml代码里面写了一个按钮,使用wx.chooseImage调用了系统相册,所以说,我们选择一张图片画进canvas也是可以的,代码如下:

wx.chooseImage({
   success: function (res) {
    that.setData({
     chooseimg: res.tempFilePaths[0]
    })
   },
})

5、下面就是cancas画图啦,画和屏幕一样宽高的,然后我们再写一行字哈哈哈,代码如下:

var that = this;
var windowW = that.data.windowW;
var windowH = that.data.windowH;
var canvasimgbg = that.data.canvasimgbg;
var canvasimg1 = that.data.chooseimg;
canvas.drawImage(canvasimgbg, 0, 0, windowW, windowH);
canvas.drawImage(canvasimg1, 0, 10, 200, 200);
canvas.setFontSize(50)
canvas.fillText('Hello', 200, 200)
canvas.draw(true,setTimeout(function(){
   that.daochu()
},1000));

使用canvas.draw()画图,完毕之后直接wx.canvasToTempFilePath导出图片

6、导出图片,代码如下:

var that = this;
var windowW = that.data.windowW;
var windowH = that.data.windowH;
wx.canvasToTempFilePath({
   x: 0,
   y: 0,
   width: windowW,
   height: windowH,
   destWidth: windowW,
   destHeight: windowH,
   canvasId: 'canvas',
   success: function (res) {
    console.log(res)
    wx.saveImageToPhotosAlbum({
     filePath: res.tempFilePath,
     success(res) {
     }
    })
    wx.previewImage({
     urls: [res.tempFilePath],
    })
   }
})

上面这些代码已经完成啦!!!

主要就是各位使用的时候看需要什么样的啦!

下面还是附上完整的代码把!

// pages/canvas/canvas.js
Page({
 /**
  * 页面的初始数据
  */
 data: {
 },
 onLoad: function (options) {
  var that = this;
  that.sys();
  that.bginfo();
 },
 sys: function () {
  var that = this;
  wx.getSystemInfo({
   success: function (res) {
    that.setData({
     windowW: res.windowWidth,
     windowH: res.windowHeight
    })
   },
  })
 },
 bginfo: function () {
  var that = this;
  wx.downloadFile({
   url: '图片链接',//注意公众平台是否配置相应的域名
   success: function (res) {
    that.setData({
     canvasimgbg: res.tempFilePath
    })
   }
  })
 },
 canvasdraw: function (canvas) {
  var that = this;
  var windowW = that.data.windowW;
  var windowH = that.data.windowH;
  var canvasimgbg = that.data.canvasimgbg;
  var canvasimg1 = that.data.chooseimg;
  canvas.drawImage(canvasimgbg, 0, 0, windowW, windowH);
  canvas.drawImage(canvasimg1, 0, 10, 200, 200);
  canvas.setFontSize(50)
  canvas.fillText('Hello', 200, 200)
  canvas.draw(true,setTimeout(function(){
   that.daochu()
  },1000));
  // canvas.draw();
 },
 daochu: function () {
  console.log('a');
  var that = this;
  var windowW = that.data.windowW;
  var windowH = that.data.windowH;
  wx.canvasToTempFilePath({
   x: 0,
   y: 0,
   width: windowW,
   height: windowH,
   destWidth: windowW,
   destHeight: windowH,
   canvasId: 'canvas',
   success: function (res) {
    console.log(res)
    wx.saveImageToPhotosAlbum({
     filePath: res.tempFilePath,
     success(res) {
     }
    })
    wx.previewImage({
     urls: [res.tempFilePath],
    })
   }
  })
 },
 chooseImage: function () {
  var that = this;
  var canvas = wx.createCanvasContext('canvas');
  wx.chooseImage({
   success: function (res) {
    that.setData({
     chooseimg: res.tempFilePaths[0]
    })
    that.canvasdraw(canvas);
   },
  })
 }
})

希望本文所述对大家微信小程序开发有所帮助。