Line dashes on Windows 200% display scale are half-size

[Phillipus]

This affects Windows only, the problem is not seen on Mac or Linux.

I've not noticed this before now because I only recently purchased a hi-res monitor. I have it set to 200% display scaling.

In Archi, our app using GEF and Draw2d, we use connection lines that have dashes. Here's an example on Windows at 100% display scaling:

And here it is at 200% scaling:

Notice how the dots are closer together in the 200% version.

This does not happen on Linux and Mac at 200% scaling, on those platforms the line dashes look the same as in the first screenshot.

[Phillipus]

Here's a Draw2d snippet to reproduce the problem.

Requirements:

• Windows
• Hi-res monitor capable of displaying at 100% and 200% scaling to compare.

import org.eclipse.draw2d.FigureCanvas;
import org.eclipse.draw2d.Polyline;
import org.eclipse.draw2d.RectangleFigure;
import org.eclipse.draw2d.geometry.Point;
import org.eclipse.draw2d.geometry.Rectangle;
import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.Color;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class LineDashesDraw2d {

    public static void main(String[] args) {
        Display display = new Display();
        Shell shell = new Shell(display);
        shell.setLayout(new FillLayout());
        shell.setSize(300, 300);

        FigureCanvas fc = new FigureCanvas(shell);
        RectangleFigure root = new RectangleFigure();
        root.setBackgroundColor(new Color(null, 255, 255, 255));
        fc.getLightweightSystem().getRootFigure().add(root);
        
        RectangleFigure rectFigure = new RectangleFigure();
        rectFigure.setBounds(new Rectangle(10, 10, 250, 150));
        rectFigure.setLineWidth(1);
        rectFigure.setLineStyle(SWT.LINE_CUSTOM);
        rectFigure.setLineDash(new float[] { 4 });
        root.add(rectFigure);

        Polyline line = new Polyline();
        line.addPoint(new Point(10, 85));
        line.addPoint(new Point(260, 85));
        line.setLineStyle(SWT.LINE_CUSTOM);
        line.setLineDash(new float[] { 4 });
        root.add(line);

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

Windows 100% scaling:

Windows 200% scaling:

[Phillipus]

The underlying issue comes from SWT:

eclipse-platform/eclipse.platform.swt#687

[azoitl]

Have you tried with intermediate scaling factors (e.g., 125% or 150%) also? Is this related to the problem I reported here: #106 (comment) ?

[Phillipus]

Have you tried with intermediate scaling factors (e.g., 125% or 150%) also? Is this related to the problem I reported here: #106 (comment) ?

Not yet. However, I did try running 4Diac IDE on Windows at 200% scaling to compare and the rendering of figures is broken (contents are displaced.)

[Phillipus]

This is fundamentally a Windows SWT issue, and I'm not sure whether it's a bug or a "feature".

For Archi, and my Draw2D fork, I've devised an ugly hack in SWTGraphics:

public void setLineDash(float[] value, boolean adjustForWindowsHiDPI) {
    if (value != null) {
        // validate dash values
        for (int i = 0; i < value.length; i++) {
            if (value[i] <= 0) {
                SWT.error(SWT.ERROR_INVALID_ARGUMENT);
            }
        }

        // HACK HERE
        if(adjustForWindowsHiDPI && "win32".equals(SWT.getPlatform()) &&
                org.eclipse.swt.internal.DPIUtil.getDeviceZoom() == 200) {
            for(int i = 0; i < value.length; i++) {
                value[i] *= 2;
            }
        }

        currentState.lineAttributes.dash = value.clone();
        currentState.lineAttributes.style = SWT.LINE_CUSTOM;
    } else {
        currentState.lineAttributes.dash = null;
        currentState.lineAttributes.style = SWT.LINE_SOLID;
    }
}

public void setLineAttributes(LineAttributes lineAttributes, boolean adjustForWindowsHiDPI) {
    copyLineAttributes(currentState.lineAttributes, lineAttributes);
    
    // HACK HERE
    if(adjustForWindowsHiDPI && currentState.lineAttributes.dash != null &&
            "win32".equals(SWT.getPlatform()) && org.eclipse.swt.internal.DPIUtil.getDeviceZoom() == 200) {
        for(int i = 0; i < currentState.lineAttributes.dash.length; i++) {
            currentState.lineAttributes.dash[i] *= 2;
        }
    }
}

[azoitl]

Have you tried with intermediate scaling factors (e.g., 125% or 150%) also? Is this related to the problem I reported here: #106 (comment) ?

Not yet. However, I did try running 4Diac IDE on Windows at 200% scaling to compare and the rendering of figures is broken (contents are displaced.)

I know that. But AFAIK this only happens if you have two screens with different scaling settings. But I don't have a clue where it is coming from. Especially as only parts are off.

[azoitl]

@Phillipus is this issue also improved throw your fix in PR #248?

No, this is still the same underlying issue in SWT.

[Phillipus]

This is now fixed upstream in SWT:

eclipse-platform/eclipse.platform.swt@e83f6dd