Bug 317180 Screen cheese when starting fresh workspace
bundles/org.eclipse.e4.ui.workbench.renderers.swt/src/org/eclipse/e4/ui/workbench/renderers/swt/CTabRendering.java
int[] points = new int[1024];
		int index = 0;
		int radius = cornerSize / 2;
		int marginWidth = parent.marginWidth;
		int marginHeight = parent.marginHeight;
		int delta = INNER_KEYLINE + OUTER_KEYLINE + 2
				* (shadowEnabled ? SIDE_DROP_WIDTH : 0) + 2 * marginWidth;
		int width = bounds.width - delta;
		int height = bounds.height - INNER_KEYLINE - OUTER_KEYLINE - 2
				* marginHeight - (shadowEnabled ? BOTTOM_DROP_WIDTH : 0);
		int circX = bounds.x + delta / 2 + radius;
		int circY = bounds.y + radius;
		
		Region clipping = new Region();
		gc.getClipping(clipping);
		Region region = new Region();
		region.add(shape);
		region.intersect(clipping);
		gc.setClipping(region);
		int header = 3; 
						
		Rectangle trim = computeTrim(PART_HEADER, state, 0, 0, 0, 0);
		trim.width = bounds.width - trim.width;
		trim.height = (parent.getTabHeight() + 1 + header) - trim.height;
		trim.x = -trim.x;
		trim.y = -trim.y;
		draw(PART_BACKGROUND, SWT.NONE, trim, gc);
		gc.setClipping(clipping);