GWT画布 - 保存图像并打开它

Question

我保存的图像中的字符串，然后当我打开它，它总是300x150

为什么图像截断？

300x150从哪里来？

代码就是你所看到的。只有2个按钮。在“PNG”

第一个保存图像，而另一个从“PNG”

    Button save = new Button("copy"); 
        save.addClickHandler(new ClickHandler() { 
         @Override 
         public void onClick(ClickEvent event) { 
          ImageElement imageElement = ImageElement.as(image.getElement()); 

          Canvas canvasTmp = Canvas.createIfSupported(); 
          Context2d context = canvasTmp.getContext2d(); 
          context.drawImage(imageElement, 0.0, 0.0, imageElement.getWidth(), imageElement.getHeight()); 
          png = canvasTmp.toDataUrl("image/png"); 
         } 
        }); 

        Button open = new Button("open"); 
        open.addClickHandler(new ClickHandler() { 

         @Override 
         public void onClick(ClickEvent event) { 

          final Image image = new Image(png); 
          vp.add(image); 
          image.addLoadHandler(new LoadHandler() { 

           @Override 
           public void onLoad(LoadEvent event) 
           { 
            Window.alert("ok"); 
           } 
          }); 

          image.addErrorHandler(new ErrorHandler() { 

           @Override 
           public void onError(ErrorEvent event) { 
            Window.alert("error"); 
           } 
          }); 

         } 
        }); 

Answer 1

画布具有300个像素的默认宽度和150个像素默认高度读取图像。创建画布之后，在绘制图像之前，请考虑这样做：

int width = imageElement.getWidth() 
int height = imageElement.getHeight() 
canvasTmp.setWidth(width + "px"); 
canvasTmp.setHeight(height + "px"); 
canvasTmp.setCoordinateSpaceWidth(width); 
canvasTmp.setCoordinateSpaceHeight(height);