Bracket selection square too small in some zooms

[akoch-yatta]

Description
The bracket selection square seems to be too small in some zooms. Some value is probably not scaled up correctly. In my opinion it is always t

Screenshot was made on 125% zoom. Lower end of the square overlaps with the bracker

Screenshot with big font on 100%

Reproduction

1. Open Java editor
2. Select a bracket to have the counterpart highlighted

Expected Behavior
The bracket highlighter should look consistent on all zooms

[al-noori]

This bug is likely to origin from rounding calculations:

The part of code where the selection square is drawn can be found in /org.eclipse.jface.text/src/org/eclipse/jface/text/source/MatchingCharacterPainter.java:

	/**
	 * Highlights the given widget region.
	 *
	 * @param gc the GC to draw into or <code>null</code> to send a redraw request
	 * @param offset the offset of the widget region
	 */
	private void draw(final GC gc, final int offset) {
		if (gc != null) {
			gc.setForeground(fColor);

			final Rectangle bounds= fTextWidget.getTextBounds(offset, offset);

			// determine the character width separately, because the getTextBounds above
			// will also include any in-line annotations (e.g. codemining annotations) in the width
			final String matchingCharacter= fTextWidget.getText(offset, offset);
			final int width= gc.textExtent(matchingCharacter).x;

			final int height= fTextWidget.getCaret().getSize().y;

			// draw box around line segment
			gc.drawRectangle(bounds.x, bounds.y + bounds.height - height, width, height - 1);
		} else {
			fTextWidget.redrawRange(offset, 1, true);
		}
	}

For a 175% Zoom and default font size, the passed height - 1 equals 14. The height of the rectangle in pixel is either 24 or 25 in some cases with the given zoom. In detail, in lines 1,2,5,6,9,10, ..., the height in pixel is 25, and in the complementary lines 3,4,7,8,11,12, ..., the height in pixel is 24. This is basically an alternating 2-2 pattern, where the first two seems good with 25 px, and the second two overlap with 24 px (see above).

One can manually test this well by selecting brackets for the named lines in the following example on a 175% zoom:

1 public class DSA { {  }
2 { }
3 { }
4 { }
5 { }
6 { }
7 { }
8 { }
9 }

For example, selecting the first bracket of the pair in line 2 leads to the following values:
bounds.x = 17
bounds.y = 15
bounds.width = 15
width = 7
height = 15.

Selecting the first one in line 3, we have:
bounds.x = 17
bounds.y = 30
bounds.width = 15
width = 7
height = 15.

But the rectangle height will be 25 px in line 2, and 24 px in line 3.

@HeikoKlare This might be of interest to you as you deal with the rounding issues. Therefore, i will unassign myself for this issue.

[akoch-yatta]

To be retested with improved logic to reduce rounding issues.

[HeikoKlare]

I was not able to reproduce this issue anymore. @al-noori can you retest again with latest state of SWT? It might be that we implicitly fixed this with:

• [Win32] Partially revert rectangle size rounding eclipse-platform/eclipse.platform.swt#2747