ADDITIONAL SYSTEM INFORMATION :
RHEL 7.3
OpenJDK11 + OpenJFX11

A DESCRIPTION OF THE PROBLEM :
SWT applications support HiDPI scaling on GTK3, so if I run an SWT app with GDK_SCALE=2, it starts properly scaled. However instantiating an FXCanvas resets the scaling, the UI is repainted with 1:1 scaling.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Set GDK_SCALE=2,
Run the below snippet (with JFX 11 and SWT 4.10 on the classpath) and click the button "Init FX"



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
SWT app starts scaled x2 and does not change after clicking the button.
ACTUAL -
SWT app starts scaled x2, but shrinks to the original scale after clicking the button.

---------- BEGIN SOURCE ----------
public class Main {
 
    public static void main(String[] args) {
        final Display display = new Display();
        final Shell shell = new Shell(display, SWT.BORDER);
        final RowLayout layout = new RowLayout();
        shell.setLayout(layout);
 
        final org.eclipse.swt.widgets.Button swtButton = new org.eclipse.swt.widgets.Button(shell, SWT.PUSH);
        swtButton.setText("Init FX");
        swtButton.addListener(SWT.Selection, event -> {
         new FXCanvas(new Shell(), SWT.NONE);
        });
 
        shell.open();
        shell.pack();
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch()) {
                display.sleep();
            }
        }
        display.dispose();
    }

}
---------- END SOURCE ----------

FREQUENCY : always