A strict check 200% image data is double the size of 100% image data

[arunjose696]

A strict check to be used only for debugging means, this ensures the imageData is scaled linearly for 100 and 200 zooms.

Steps to reproduce

Out of the blow snippets. Snippet1 which uses an image data provider that always returns the same image, when executed with the VM argument -Dorg.eclipse.swt.internal.enableStrictChecks=True, logs the error` "ImageData should be linearly scaled across zooms." to stdout. Whereas snippet 2 which scales ImageData linearly runs without this error log.

snippet 1

package org.eclipse.swt.snippets;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.*;
public class TestImageProvider {
    public static void main(String[] args) {
        Display display = new Display();
        ImageDataProvider provider = (zoom) -> new ImageData(
            16, 16, 32,
            new PaletteData((new RGB(255, 0, 0)))
        );
        Image image = new Image(display, provider);
        System.out.println("Done execution");
    }
}

snippet 2

package org.eclipse.swt.snippets;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.*;
public class TestImageProvider {
    public static void main(String[] args) {
        Display display = new Display();
        ImageDataProvider provider = (zoom) -> new ImageData(
            16*zoom/100, 16*zoom/100, 32,
            new PaletteData((new RGB(255, 0, 0)))
        );
        Image image = new Image(display, provider);  
        System.out.println("Done execution");
    }
}

The below examples demonstrate testing this again with PNG images. In the first snippet, the ImageDataProvider returns the image data from the same file for both 100% and 200% zoom levels without scaling, which causes the error message "ImageData should be linearly scaled across zooms." to be printed to stdout. In the second snippet it provides properly scaled image data at 200% zoom (using a scaled image), so it executes without logging this error.
To run these snippets, download the following PNG files and place them in your working directory:
pause.png

[email protected]

snippet 1

package org.eclipse.swt.snippets;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.*;
public class TestImageProvider {
    public static void main(String[] args) {
    	System.out.println("Working directory: " + System.getProperty("user.dir"));
        Display display = new Display();

        ImageDataProvider provider = zoom -> {
            if (zoom == 100) {
                return new ImageData("pause.png");
            }
            else if (zoom == 200) {
                return new ImageData("pause.png");
            }
            else {
                return null;
            }
        };

        Image image = new Image(display, provider);
        System.out.println("Done execution");
    }
}

snippet 2

package org.eclipse.swt.snippets;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.*;
public class TestImageProvider {
    public static void main(String[] args) {
    	System.out.println("Working directory: " + System.getProperty("user.dir"));
        Display display = new Display();

        ImageDataProvider provider = zoom -> {
            if (zoom == 100) {
                return new ImageData("pause.png");
            }
            else if (zoom == 200) {
                return new ImageData("[email protected]");
            }
            else {
                return null;
            }
        };

        Image image = new Image(display, provider);
        System.out.println("Done execution");
    }
}

[github-actions]

Test Results

   539 files   -  6     539 suites   - 6   27m 41s ⏱️ - 1m 13s
 4 369 tests  - 37   4 353 ✅  - 35   15 💤  - 3  0 ❌ ±0  1 🔥 +1 
16 708 runs   - 37  16 568 ✅  - 35  139 💤  - 3  0 ❌ ±0  1 🔥 +1 

For more details on these errors, see this check.

Results for commit c40fee2. ± Comparison against base commit 6842283.

This pull request removes 37 tests.

AllWin32Tests org.eclipse.swt.graphics.ImageWin32Tests ‑ testImageDataForDifferentFractionalZoomsShouldBeDifferent
AllWin32Tests org.eclipse.swt.graphics.ImageWin32Tests ‑ testImageShouldHaveDimesionAsPerZoomLevel
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testByteArrayTransfer
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testFileTransfer
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testHtmlTransfer
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testImageTransfer_fromCopiedImage
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testImageTransfer_fromImage
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testImageTransfer_fromImageData
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testImageTransfer_fromImageDataFromImage
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testRtfTransfer
…

♻️ This comment has been updated with latest results.

[arunjose696]

In CI failing checks I have the below error, Dont think this has anything to do with my changes.

[2025-07-01T10:06:14.756Z] [ERROR] Failed to execute goal org.eclipse.tycho.extras:tycho-p2-extras-plugin:5.0.0-SNAPSHOT:compare-version-with-baselines (compare-attached-artifacts-with-release) on project org.eclipse.swt.tools: Baseline and reactor have the same fully qualified version, but different content
[2025-07-01T10:06:14.756Z] [ERROR] different
[2025-07-01T10:06:14.756Z] [ERROR]    META-INF/ECLIPSE_.RSA: present in baseline only
[2025-07-01T10:06:14.756Z] [ERROR]    META-INF/ECLIPSE_.SF: present in baseline only
[2025-07-01T10:06:14.756Z] [ERROR] -> [Help 1]
[2025-07-01T10:06:14.756Z] org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.eclipse.tycho.extras:tycho-p2-extras-plugin:5.0.0-SNAPSHOT:compare-version-with-baselines (compare-attached-artifacts-with-release) on project org.eclipse.swt.tools: Baseline and reactor have the same fully qualified version, but different content
[2025-07-01T10:06:14.756Z] different
[2025-07-01T10:06:14.756Z]    META-INF/ECLIPSE_.RSA: present in baseline only
[2025-07-01T10:06:14.756Z]    META-INF/ECLIPSE_.SF: present in baseline only

[fedejeanne]

Some comments before I move to the testing phase

[fedejeanne]

Why throw an exception here? I thought this check was only for debugging purposes like other checks we added before (#1979, #1803, #1753)

@akoch-yatta ?

[arunjose696]

Replaced exception with a System.err.println()

[fedejeanne]

In that case you'll have to remove the 2 new tests since there is no way to test that something was written to the console

[fedejeanne]

And you should adapt the text of this PR since nothing fails, one simply sees some output in the console. Please also add a snippet to test by providing 2 image files, one of them (the _@2x) having the wrong size.

[arunjose696]

I’ve updated the PR text . I also added the two snippets one with an ImageDataProvider that scales the image data correctly and one that doesn’t.

To keep the setup simple, I didn’t use actual image files (e.g. SVGs), since that would require uploading multiple files and slightly complicate the example. Let me know if including real images is still necessary

[fedejeanne]

It is necessary, that is a valid use case and it should be tested too.

[arunjose696]

In PR text I’ve now added tests using actual .png image files in addition to the earlier code snippets.

I’m still a bit unclear on why this was necessary, as I thought the original snippets already demonstrated the intended behavior with the case where ImageData is unscaled. That said, I’ve still added a snippet with real images as requested. Please let me know if this is what you had in mind, or if there’s another use case I should be covering.

[fedejeanne]

You're right, I had the wrong expectation about this PR.

FTR what I wanted to test is in JFace and you could see it for example by adding a modified version of validateLinearScaling that takes ImageDescriptor as a parameter and calling it at the end of org.eclipse.jface.tests.images.FileImageDescriptorTest.testAdaptToURL(). If you do that and provide a second file that adds @2x to the end of the file but it does not have double the size then the check would fail.

Since I'm not on Windows at the moment, I can't test this PR- I'll get back to it later this week.