Scaling an Image in GWT

java gwt image-scaling
Daniel picture Daniel · Feb 14, 2010 · Viewed 30.3k times · Source

Changing the size of an Image Widget in GWT changes the size of the image element, but does not rescale the image on the screen. Therefore, the following will not work: 

Image image = new Image(myImageResource);
image.setHeight(newHeight);
image.setWidth(newWidth);
image.setPixelSize(newWidth, newHeight);

This is because GWT implements its Image widget by setting the background-image of the HTML <img... /> element as the image, using CSS.

How does one get the actual image to resize?

Answer

Daniel picture Daniel · Feb 14, 2010

I saw this blog entry, which solves the problem by using a GWT DataResource instead of ImageResource. It turns out that the same technique will actually work with ImageResource, if you use it as follows:

Image image = new Image(myImageResource.getURL());
image.setPixelSize(getLength(), getHeight());

To keep aspect ratio calculate it like:

Image image = new Image(myImageResource.getURL());
image.setPixelSize(newWidth, myImageResource.getHeight() * newWidth / myImageResource.getWidth());

As of GWT 2.4, use (see here):

Image image = new Image(myImageResource.getSafeUri());
image.setPixelSize(newWidth, myImageResource.getHeight() * newWidth / myImageResource.getWidth());

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