Adjust selection bounds for CTabRenderring

Selected tabs highlight look slightly off and more noticeable when zoom
is not 100%. These adjusted value shows no gaps from top and better
aligned highlights for tabs (Theme is enabled)

Author: ShahzaibIbrahim

bundles/org.eclipse.e4.ui.workbench.renderers.swt/src/org/eclipse/e4/ui/workbench/renderers/swt/CTabRendering.java

@@ -18,6 +18,7 @@
 package org.eclipse.e4.ui.workbench.renderers.swt;
 
 import java.lang.reflect.Field;
+import java.util.Arrays;
 import java.util.Objects;
 import org.eclipse.core.runtime.Platform;
 import org.eclipse.core.runtime.preferences.IEclipsePreferences;
@@ -627,11 +628,28 @@ void drawSelectedTab(int itemIndex, GC gc, Rectangle bounds) {
 				highlightOnTop = !highlightOnTop;
 			}
 			int highlightHeight = 2;
-			int verticalOffset = highlightOnTop ? 0 : bounds.height - (highlightHeight - 1);
-			int horizontalOffset = itemIndex == 0 || cornerSize == SQUARE_CORNER ? 0 : 1;
-			int widthAdjustment = cornerSize == SQUARE_CORNER ? 0 : 1;
-			gc.fillRectangle(bounds.x + horizontalOffset, bounds.y + verticalOffset, bounds.width - widthAdjustment,
-					highlightHeight);
+			if (highlightOnTop == onBottom) {
+				int verticalOffset = bounds.height - (highlightHeight);
+				gc.fillRectangle(outlineBoundsForOutline.x, bounds.y + verticalOffset, outlineBoundsForOutline.width,
+						highlightHeight);
+				gc.setForeground(selectedTabHighlightColor);
+				gc.drawLine(outlineBoundsForOutline.x, bounds.y + verticalOffset + highlightHeight,
+						outlineBoundsForOutline.x + outlineBoundsForOutline.width,
+						bounds.y + verticalOffset + highlightHeight);
+			} else if (cornerSize == SQUARE_CORNER) {
+				gc.fillRectangle(outlineBoundsForOutline.x,
+						outlineBoundsForOutline.y, outlineBoundsForOutline.width, highlightHeight + 1);
+			} else {
+				boolean gcAdvanced = gc.getAdvanced();
+				gc.setAdvanced(false);
+				int[] highlightShape = Arrays.copyOfRange(tabOutlinePoints, 12, tabOutlinePoints.length - 12);
+				int highlightY = highlightOnTop ? highlightHeight
+						: outlineBoundsForOutline.height - highlightHeight;
+				highlightShape[1] = highlightShape[3] = highlightShape[highlightShape.length
+						- 1] = highlightShape[highlightShape.length - 3] = highlightY;
+				gc.fillPolygon(highlightShape);
+				gc.setAdvanced(gcAdvanced);
+			}
 		}
 
 		if (backgroundPattern != null) {