微信小程序 Canvas 画板使用,踩坑记录_canvas.width = res[0].width canvas.height = res[0]

微信小程序 Canvas 2dAPI的绘图使用

Html

 <!-- canvas 画板 -->
<view :class="showCanvasCSS" >
	<canvas
	  type="2d"
	  id="canvas"
	  class='canvas-style'
	  />
<view class="linkcopy">
<u-button class="linkcopyBtn" icon="download" type="info"  @click="CloseCanvas">取消</u-button>
<u-button class="linkcopyBtn" icon="download" type="primary"  @click="uploads">保存图片</u-button>
</view>
</view>

CSS

.canvas-style{
	margin: 0 auto;
	width: 100%;
	height: 990rpx;
	// border: 1px solid black;
}
.container{
	z-index: 3;
	position: fixed;
	top:150rpx;
	width: 100%;
	height: 1100rpx;
	// border: 1px solid red;
}
.container2{
	position: fixed;
	left:9950rpx;
	width: 100%;
	height: 1100rpx;
	
	// border: 1px solid red;
}
.linkcopy{
	width: 100%;
}
.linkcopyBtn{
	display: inline-block;
	float: left;
	margin-top: 25rpx;
	margin-left: 25rpx;
	width: 45%;
	height: 350rpx;
}

js

//初始化画板 - 微信小程序 canvas 2D
			drawing(){
			    	//定义全局canvas
			       const query = wx.createSelectorQuery();
			       query
			       	.select('#canvas')
			       	.fields({ node: true, size: true })
			       	.exec((res) => {
			       		const canvas = res[0].node;
			       		this.canvasObj=canvas;
			            const ctx = canvas.getContext('2d');
			       		const dpr = wx.getSystemInfoSync().pixelRatio;
			       		canvas.width = res[0].width * dpr;
			       		canvas.height = res[0].height * dpr;
						this.canvasWidth=res[0].width * dpr;
						this.canvasHeight = res[0].height * dpr;
			       		ctx.scale(dpr, dpr);
					// 填充一个白色矩形
					ctx.fillStyle ='white';
					ctx.fillRect(8, 55, 345,425);
			    	//头部图片
					const headerImg = canvas.createImage();
					headerImg.src = this.TopList.product_image_url;
					headerImg.onload = () => {
						ctx.drawImage(headerImg, 83, 65, 200, 186);
					};
			    	// 标题
			        ctx.fillStyle ='#333333';
			        ctx.font = 'normal bold 15px sans-serif';
			        ctx.fillText(this.TopList.brand_name+" | "+this.TopList.gpc_product.FNAME+" | "+this.TopList.gpc_product.FSPECIFICATION, 20, 270);
					
			        // 二维码
					const QRcodeImg = canvas.createImage();
					QRcodeImg.src = this.QRcodeImg;
					QRcodeImg.onload = () => {
						ctx.drawImage(QRcodeImg, 215, 345, 124.5, 130);
					};
					//logo
					const logoImg = canvas.createImage();
					logoImg.src = this.logoImg;
					logoImg.onload = () => {
						ctx.drawImage(logoImg, 25, 345, 180, 80);
					};
					
			        })
			},

截图保存分享

//下载画板生成图片
			    uploads() {
			        var that = this;
			        var timer  = setTimeout(function(){
			          wx.canvasToTempFilePath({
			            x: 8,
			            y: 55,
			            width: 345,
			            height: 425,
			            destWidth: this.canvasWidth,
			            destHeight: this.canvasHeight,
			            canvas: that.canvasObj,
			            success(res) {
			              wx.saveImageToPhotosAlbum({
			                filePath: res.tempFilePath,
			                success: function (data) {
			                  wx.showToast({
			                    title: '保存成功，快去分享吧',
			                    icon: 'none',
			                    duration: 2000
			                  });
							  that.showCanvas=false;
							  that.showCanvasCSS="container2";
			                  clearTimeout(timer);
			                },
			                fail: function (error) {
			                  console.log(error)
			                  wx.showToast({
			                    title: '很遗憾，保存失败',
			                    icon: 'none',
			                    duration: 2000
			                  })
			                  clearTimeout(timer)
			                }
			              })
			            }
			          })
			        },1000)
			    }

注：需要注意的是，对于Canvas画板需要隐藏/显示，运用wx:if 、v-if、v-show、hidden都不可行，解决方案为将canvas设置定位，比如，然后指定left一个比较大的值，让canvas的显示超出屏幕范围。

  <canvas canvas-id='canOne' class='canOne' style='width:1080px;height:1643px;position:fixed;left:9000px;'></canvas>

微信小程序 Canvas 旧版API的绘图使用 鉴转载：
 

https://blog.csdn.net/javascript411/article/details/95466716