Non-blurred SVG image scaling with GC.drawImage(Image image, int destX, int destY, int destWidth, int destHeight) only works on Windows unless an ImageFileNameProvider is used

[Phillipus]

• Eclipse 4.38

According to this:

When using the new drawImage method, images that can provide size-specific data (such as SVGs) are loaded at the destination size, avoiding blurry scaling.

However that's not the case for Mac or Linux unless an ImageFileNameProvider is used.

Run this Snippet on Windows, Mac and Linux and compare the results:

import java.nio.file.Path;
import org.eclipse.swt.graphics.Color;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.graphics.ImageFileNameProvider;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class SVGImageTests {
    
    public static void main(String[] args) throws Exception {
        final Display display = new Display();

        final Shell shell = new Shell(display);
        shell.setText("SVG Image Test");
        shell.setLayout(new FillLayout());
        shell.setBounds(250, 50, 1000, 400);
        shell.setBackground(new Color(255, 255, 255));
        
        String imgPath = "image.svg";
        Path fullPath = Path.of(SVGImageTests.class.getResource(imgPath).toURI());
        
        // Image loaded in stream
        Image image1 = new Image(display, SVGImageTests.class.getResourceAsStream(imgPath));

        // Image loaded in file path
        Image image2 = new Image(display, fullPath.toString());
        
        // Image loaded in ImageFileNameProvider
        Image image3 = new Image(display, (ImageFileNameProvider) zoom -> {
            return zoom == 100 ? fullPath.toString() : null;
        });
        
        shell.addPaintListener(e -> {
            e.gc.drawImage(image1, 20, 10, 300, 300);
            e.gc.drawText("Image(Display, InputStream)", 80, 300);
            
            e.gc.drawImage(image2, 340, 10, 300, 300);
            e.gc.drawText("Image(Display, String)", 420, 300);
            
            e.gc.drawImage(image3, 660, 10, 300, 300);
            e.gc.drawText("Image(Display, ImageFileNameProvider)", 700, 300);
        });
        
        shell.open();

        while(!shell.isDisposed()) {
            if(!display.readAndDispatch()) {
                display.sleep();
            }
        }

        display.dispose();
    }
}

Use this SVG image for the Snippet:

Here's the outputs...

On Windows all Image methods result in sharp output:

On Mac only using ImageFileNameProvider is sharp:

On Linux only using ImageFileNameProvider is sharp:

[HeikoKlare]

You are right that on MacOS and Linux the support is limited to ImageFileNameProvider and the not-yet-API ImageDataAtSizeProvider and that the news is obviously misleading in that regard.

The Image(display, filename) constructor actually rather works by accident on Windows, because on Windows the filename is wrapped into an ImageFileNameProvider. We could probably easily do the same on Linux and MacOS to support sharp rendering of SVGs with the new drawImage method.
We did not implement support for the InputStream constructor because it requires additional storage of the input stream data. On Windows this data is stored anyway (for on-demand creation of handles for arbitrary zooms). But we should definitely add that to properly support the sharp rendering of SVGs passed as InputStream with the new drawImage method. We will take care of that.

[Phillipus]

On Windows this data is stored anyway (for on-demand creation of handles for arbitrary zooms). But we should definitely add that to properly support the sharp rendering of SVGs passed as InputStream with the new drawImage method. We will take care of that.

I'm implementing the rendering of SVG images using GC.drawImage(Image, x, y, width, height) in our RCP app so that they look sharp on all platforms. However because the image bytes are loaded from a zip file we can only use the InputStream Image creation. I've implemented a workaround that saves the image bytes to a temporary file and loads back in again via an ImageFileNameProvider but if there was some other way to load via InputStream on Mac and Linux that would be perfect.

[Phillipus]

@HeikoKlare BTW - many thanks for your feedback and help with these issues, I appreciate it. :-)

[HeikoKlare]

We will definitely provide a solution in SWT for this so that you can hopefully remove your workarounds soon, but it will of course only be available with I-Builds or the 4.39 release.

One additional effect of the missing storage of the InputStream content of an image is that on Linux/GTK such an image cannot be refreshed for a different zoom. There is the Image#refreshImageForZoom() method that regenerates the image data/handle for a modified zoom, but there is no implementation for an image based on an InputStream as the necessary data is not present. That is something that may be fixed together with the support for the sharp rendering with GC#drawImage() as well. We will try to incorporate that in a fix.

many thanks for your feedback and help with these issues, I appreciate it. :-)

You're welcome. Thanks to you for opening the issues and providing perfect snippets to reproduce right away. We work on Windows most of the time (because our product is Windows only) such that we find issues/inconsistencies on MacOS and Linux not so easily. So this kind of feedback is very valuable and highly appreciated :-)