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);
},
})
}
})有用的话可以支持一下，谢谢！！！
