CODEWITHSUNDEEP
javaswt
John Smith
John Smith

Reputation: 6197

Java, SWT, the image transparencity gets lost when resizing

Im displaying .png image with transparencity which works well by default... until I resize the image:

public Image resize(Image image, int width, int height)
{
    Image scaled = new Image(Display.getDefault(), width, height);
    scaled.getImageData().transparentPixel = image.getImageData().transparentPixel;
    GC gc = new GC(scaled);
    gc.setAntialias(SWT.ON);
    gc.setInterpolation(SWT.HIGH);
    gc.drawImage(image, 0, 0,image.getBounds().width, image.getBounds().height, 0, 0, width, height);
    gc.dispose();
    return scaled;
}

then the transparency is gone, I can see the "white" color

Upvotes: 1

Views: 299

Answers (1)

greg-449
greg-449

Reputation: 111142

getImageData() gives you a copy of the image data so setting the transparent pixel on that does not change the original image.

Instead you need to create another image from the scaled image data with the transparent pixel set. So something like:

Image scaled = new Image(Display.getDefault(), width, height);
GC gc = new GC(scaled);
gc.setAntialias(SWT.ON);
gc.setInterpolation(SWT.HIGH);
gc.drawImage(image, 0, 0,image.getBounds().width, image.getBounds().height, 0, 0, width, height);
gc.dispose();

// Image data from scaled image and transparent pixel from original

ImageData imageData = scaled.getImageData();

imageData.transparentPixel = image.getImageData().transparentPixel;

// Final scaled transparent image

Image finalImage = new Image(Display.getDefault(), imageData);

scaled.dispose();

Note that this only works when the original image data has the same format as the scaled image data (particularly the palette data)

If the data is in a different format use:

ImageData origData = image.getImageData();

imageData.transparentPixel = imageData.palette.getPixel(origData.palette.getRGB(origData.transparentPixel));

Upvotes: 2

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