微信小程序“圣诞帽”的实现思路详解

wx.getUserInfo({
    success: function(res) {
        var userInfo = res.userInfo
        var avatarUrl = userInfo.avatarUrl
  }
})

wx.downloadFile({   
    url: userInfo.avatarUrl, 
    success: function (res) {    
        if (res.statusCode === 200) {      
            avatarUrl = res.tempFilePath //这里的地址是指向本地图片 
        }     
    }  
})

drawAvatar: function (img) {
    ctx.drawImage(img, 0, 0, avatarImg.w, avatarImg.h)
}

var hat = { 
    url: "../res/hat01.png", 
    w: 40,  
    h: 40,  
    x: 100, 
    y: 100, 
    b: 1,//缩放的倍率
    rotate: 0//旋转的角度
}

drawHat: function (hat) { 
    ctx.translate(hat.x, hat.y) 
    ctx.scale(hat.b, hat.b) 
    ctx.rotate(hat.rotate * Math.PI / 180) 
    ctx.drawImage(hat.url, -hat.w / 2, -hat.h / 2, hat.w, hat.h) 
}

ctx.translate(hat.x, hat.y) //translate是将画布的中心点移动到指定坐标处

ctx.drawImage(hat.url, -hat.w / 2, -hat.h / 2, hat.w, hat.h)

moveHat: function (e) { 
     hat.x = e.touches[0].x
     hat.y = e.touches[0].y 
     that.drawA() 
 }

rotateHat: function (e) {  
     hat.rotate = e.detail.value    //这一块偷懒了，用slider组件 ，滑动取值
     that.drawA() 
 }

scaleHat: function (e) {  
     hat.b = e.detail.value   
     hat.w = 40 * hat.b    
     hat.h = 40 * hat.b    
     that.drawA()    ////此处用slider组件 ，滑动取值 
}

changeHat: function (e) {
    hat.url = e.currentTarget.dataset.url  //改变帽子的样式   
    that.drawA() 
}

saveToPhoto: function () {
    wx.canvasToTempFilePath({  
        x: 0,
        y: 0,
        width: 240,
        height: 240,
        destWidth: 240,
        destHeight: 240,
        canvasId: 'ctx',
        success: function (res) {
            //canvas转图片成功回调
        }
    })
}

wx.saveImageToPhotosAlbum({
    filePath: res.tempFilePath,
}) 
wx.showToast({title: '保存成功'})