在2.9.4微信基础库 不行 在2.6.0基础库的时候又可以？

绘图后截图 未画到的区域应该是透明的才对 但是现在显示的图片 透明区域是黑色的

[图片]   let canvas = document.createElement('canvas');         canvas.width = width;         canvas.height = height;         let ctx = canvas.getContext('2d');         let gpTexture = new cc.RenderTexture(); //绘制         //@ts-ignore         gpTexture.initWithSize(width, height, cc.game._renderContext.STENCIL_INDEX8);         this.gpCamera.targetTexture = gpTexture;         this.gpCamera.render(this.node);//相机绘制，将屏幕上的内容更新到renderTexture中         let data = gpTexture.readPixels();//读取renderTexture中的数据         // data = this.changeAlpha(data);         let rowBytes = width * 4;         for (let row = 0; row < height; row++) {             let srow = height - 1 - row;             let imageData = ctx.createImageData(width, 1);             let start = srow * width * 4;             for (let i = 0; i < rowBytes; i++) {                 imageData.data[i] = data[start + i];             }             ctx.putImageData(imageData, 0, row);         }   let _tempFilePath = await canvas.toTempFilePathSync(                 {                     x: 0,                     y: 0,                     width: width,                     height: height,                     destWidth: 380,                     destHeight: 380,                     fileType: 'png',                     quality: 1                 });             wx.previewImage({                 urls: [_tempFilePath]              })

[图片][图片]   let canvas = document.createElement('canvas');         canvas.width = width;         canvas.height = height;         let ctx = canvas.getContext('2d');         let gpTexture = new cc.RenderTexture(); //绘制         //@ts-ignore         gpTexture.initWithSize(width, height, cc.game._renderContext.STENCIL_INDEX8);         this.gpCamera.targetTexture = gpTexture;         this.gpCamera.render(this.node);//相机绘制，将屏幕上的内容更新到renderTexture中         let data = gpTexture.readPixels();//读取renderTexture中的数据         // data = this.changeAlpha(data);         let rowBytes = width * 4;         for (let row = 0; row < height; row++) {             let srow = height - 1 - row;             let imageData = ctx.createImageData(width, 1);             let start = srow * width * 4;             for (let i = 0; i < rowBytes; i++) {                 imageData.data[i] = data[start + i];             }             ctx.putImageData(imageData, 0, row);         }   let _tempFilePath = await canvas.toTempFilePathSync(                 {                     x: 0,                     y: 0,                     width: width,                     height: height,                     destWidth: 380,                     destHeight: 380,                     fileType: 'png',                     quality: 1                 });             wx.previewImage({                 urls: [_tempFilePath]              }) 明明是透明部分 怎么就变成黑色了