Scale Tree.GRID_WIDTH by zoom level instead of using fixed pixels

[ShahzaibIbrahim]

The Tree.GRID_WIDTH constant specifies the extra width added to a tree item when lines between columns are visible (lineVisible = true). This compensates for the space taken by the grid line. Previously, this was defined as a fixed pixel value, which appeared too small on high-DPI monitors.

This change redefines GRID_WIDTH in points and converts it to pixels based on the current zoom level, ensuring consistent column spacing across different display scales.

How To Test

• Run the following snippet in 200% zoom

import org.eclipse.swt.*;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.widgets.*;

public class LinesVisibleTreeExample {

public static void main (String [] args) {
	System.setProperty("swt.autoScale", "quarter");
	System.setProperty("swt.autoScale.updateOnRuntime", "true");
	Display display = new Display ();
	Shell shell = new Shell (display);
	shell.setText("Snippet 15");
	shell.setLayout(new FillLayout());
	final Tree tree = new Tree (shell, SWT.BORDER);
	tree.setLinesVisible(true);
	TreeColumn treeColumn = new TreeColumn(tree, SWT.NONE);
	treeColumn.setText("TreeColumn");
	for (int i=0; i<4; i++) {
		TreeItem iItem = new TreeItem (tree, 0);
		iItem.setText ("TreeItem (0) -" + i);
		for (int j=0; j<4; j++) {
			TreeItem jItem = new TreeItem (iItem, 0);
			jItem.setText ("TreeItem (1) -" + j);
			for (int k=0; k<4; k++) {
				TreeItem kItem = new TreeItem (jItem, 0);
				kItem.setText ("TreeItem (2) -" + k);
				for (int l=0; l<4; l++) {
					TreeItem lItem = new TreeItem (kItem, 0);
					lItem.setText ("TreeItem (3) -" + l);
				}
			}
		}
	}
	treeColumn.pack();
	shell.setSize (200, 200);
	shell.open ();
	while (!shell.isDisposed()) {
		if (!display.readAndDispatch ()) display.sleep ();
	}
	display.dispose ();
}
}

Currently, since lines are visible, we add 1 point to the item width by default. With this change, the value is now defined in points and scaled to pixels, resulting in 2px at 200% zoom. Although the visual difference is negligible, this ensures consistency by keeping all such constants defined in points and scaled according to the zoom level.

[github-actions]

Test Results

   546 files  + 7     546 suites  +7   29m 15s ⏱️ - 6m 1s
 4 426 tests +54   4 409 ✅ +70   17 💤 +3  0 ❌  - 6 
16 750 runs  +54  16 623 ✅ +70  127 💤 +3  0 ❌  - 6 

Results for commit 9d8eb7c. ± Comparison against base commit 3444886.

♻️ This comment has been updated with latest results.

[akoch-yatta]

@ShahzaibIbrahim While reviewing, I noticed that here Table.GRID_WIDTH is used in Tree for some reason. Can you adapt this place in this PR as well, please

[akoch-yatta]

As stated in the PR, the visual difference is neglectable it still makes sense to treat this magic number properly as point instead of pixel. Changes look sound and I didn't find any problems when testing the changes.