如何从手机中选择文件并绘制在convas上？
由于<image>不能对图像进行逐像素的处理，所以需要用到convas，但是convas绘图一直不成功，请问有什么解决的办法？ [代码]selectImage: [代码][代码]function[代码][代码](index) {[代码][代码] [代码][代码]var[代码] [代码]that = [代码][代码]this[代码][代码];[代码][代码] [代码][代码]var[代码] [代码]c = wx.createCanvasContext([代码][代码]'firstCanvas'[代码][代码]);[代码][代码] [代码][代码]var[代码] [代码]img_path = [代码][代码]new[代码] [代码]String();[代码][代码] [代码][代码]wx.chooseImage({[代码][代码] [代码][代码]count: 1,[代码][代码] [代码][代码]sizeType: [[代码][代码]'original'[代码][代码], [代码][代码]'compressed'[代码][代码]], [代码][代码]// 可以指定是原图还是压缩图，默认二者都有 [代码][代码] [代码][代码]sourceType: [[代码][代码]'album'[代码][代码], [代码][代码]'camera'[代码][代码]], [代码][代码]// 可以指定来源是相册还是相机，默认二者都有 [代码][代码] [代码][代码]success: [代码][代码]function[代码][代码](res0) {[代码][代码] [代码][代码]// 返回选定照片的本地文件路径列表，tempFilePath可以作为img标签的src属性显示图片[代码][代码] [代码][代码]img_path = res0.tempFilePaths[0];[代码][代码] [代码][代码]console.log([代码][代码]'get path'[代码][代码]);[代码][代码] [代码][代码]that.setData({[代码][代码] [代码][代码]img_path: res0.tempFilePaths[代码][代码] [代码][代码]});[代码][代码] [代码] [代码] [代码][代码]wx.getImageInfo({[代码][代码] [代码][代码]src: img_path,[代码][代码] [代码][代码]success: [代码][代码]function[代码][代码](res1) {[代码][代码] [代码][代码]screen.w = res1.width;[代码][代码] [代码][代码]screen.h = res1.height;[代码][代码] [代码][代码]c.drawImage(res1.path, 0, 0, screen.w, screen.h);[代码][代码] [代码][代码]wx.canvasGetImageData({[代码][代码] [代码][代码]canvasId: [代码][代码]"firstCanvas"[代码][代码], [代码][代码]//参数，canvas标签的id[代码][代码] [代码][代码]x: 0, [代码][代码]//起始位置，x坐标[代码][代码] [代码][代码]y: 0,[代码][代码] [代码][代码]width: 100,[代码][代码] [代码][代码]height: 100,[代码][代码] [代码][代码]success: [代码][代码]function[代码][代码](res2)[代码] [代码] [代码][代码]{[代码][代码] [代码][代码]//引入upng，将图片转化成utf-8格式[代码][代码] [代码][代码]let pngData = upng.encoded([res.data.buffer].res.width, res.height)[代码][代码] [代码][代码]//再转化成base64[代码][代码] [代码][代码]let bs64 = wx.arrayBufferToBase64(pngData)[代码][代码] [代码][代码]console.log([代码][代码]'1'[代码][代码])[代码][代码] [代码][代码]},[代码][代码] [代码][代码]fail: [代码][代码]function[代码][代码](error) {[代码][代码] [代码][代码]console.log(error) // 报错：errMsg: "canvasGetImageData: fail canvas is empty"[代码][代码] [代码][代码]},[代码][代码] [代码][代码]complete: [代码][代码]function[代码][代码](res) {[代码][代码] [代码][代码]console.log([代码][代码]'over'[代码][代码])[代码][代码] [代码][代码]},[代码][代码] [代码][代码]});[代码][代码] [代码][代码]}[代码][代码] [代码][代码]});[代码] [代码] [代码][代码]}[代码][代码] [代码][代码]})[代码]
