Use baseline instead of centerline in PlotRenderer

If the text extent height of a to be rendered plot line is odd, then the
SWTPlotRenderer cannot calculate the correct Y position for drawing the
label and draws the label with a 1 pixel offset. SWT text drawing uses
the baseline as Y coordinate. Due to the given centerline API in the
AbstractPlotRenderer the overall calculation of the baseline for SWT is
effectively (height / 2) * 2, thereby rounding all odd heights downward
to the next even number.

This change pushes the division by 2 from the caller into the
implementations of drawText. A corresponding change will be pushed in
the egit repository.

Bug: 450813
Change-Id: I66f4e71873bb8e6f936fde573bbe4c35fe23a022
Signed-off-by: Michael Keppler <michael.keppler@gmx.de>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.ui/src/org/eclipse/jgit/awtui/AWTPlotRenderer.java

@@ -123,7 +123,7 @@ final class AWTPlotRenderer extends AbstractPlotRenderer<SwingLane, Color>
 	@Override
 	protected void drawText(final String msg, final int x, final int y) {
 		final int texth = g.getFontMetrics().getHeight();
-		final int y0 = y - texth/2 + (cell.getHeight() - texth)/2;
+		final int y0 = (y - texth) / 2 + (cell.getHeight() - texth) / 2;
 		g.setColor(cell.getForeground());
 		g.drawString(msg, x, y0 + texth - g.getFontMetrics().getDescent());
 	}

org.eclipse.jgit/src/org/eclipse/jgit/revplot/AbstractPlotRenderer.java

@@ -174,7 +174,7 @@ public abstract class AbstractPlotRenderer<TLane extends PlotLane, TColor> {
 		}
 
 		final String msg = commit.getShortMessage();
-		drawText(msg, textx + dotSize, h / 2);
+		drawText(msg, textx + dotSize, h);
 	}
 
 	/**
@@ -276,9 +276,9 @@ public abstract class AbstractPlotRenderer<TLane extends PlotLane, TColor> {
 	 *            first pixel from the left that the text can be drawn at.
 	 *            Character data must not appear before this position.
 	 * @param y
-	 *            pixel coordinate of the centerline of the text.
-	 *            Implementations must adjust this coordinate to account for the
-	 *            way their implementation handles font rendering.
+	 *            pixel coordinate of the baseline of the text. Implementations
+	 *            must adjust this coordinate to account for the way their
+	 *            implementation handles font rendering.
 	 */
 	protected abstract void drawText(String msg, int x, int y);