How display a resized image with aspect ratio preserved in a fixed size Label in eclipse e4 rcp?

Question

I want to display a preview image which is a resized version of the original image with aspect ratio preserved in a fixed size Label. For example, I have an image of 1024x786 and I want to display it in a Label which has size 500x500. I want it to fit in this label keeping the aspect ratio of the image intact.

It would also be nice if the image could be automatically resized when a user resizes the part.

Is it possible to do this with Label? or do I need a canvas for this?

Answer 1

This image scaling code is based on JFace ImageDescriptor:

ImageDescriptor scaleImage(Display display, ImageDescriptor imageDesc,
                           int maxWidth, int maxHeight)
{
  if (imageDesc == null)
    return null;

  ImageData imageData = imageDesc.getImageData();
  if (imageData == null)    // Can by JPEG using CMYK colour space etc.
    return imageDesc;

  int newHeight = maxHeight;
  int newWidth = (imageData.width * newHeight) / imageData.height;
  if (newWidth > maxWidth)
   {
     newWidth = maxWidth;
     newHeight = (imageData.height * newWidth) / imageData.width;
   }

  // Use GC.drawImage to scale which gives better result on Mac

  Image newImage = new Image(display, newWidth, newHeight);

  GC gc = new GC(newImage);

  Image oldImage = imageDesc.createImage();

  gc.drawImage(oldImage, 0, 0, imageData.width, imageData.height, 0, 0, newWidth, newHeight);

  ImageDescriptor result = ImageDescriptor.createFromImage(newImage);

  oldImage.dispose();
  gc.dispose();

  return result;
}