Fix drawPolyline. Issue #148

[DieterMai]

Fix for Issue #148

[github-actions]

Test Results

   338 files  ±0     338 suites  ±0   2m 6s ⏱️ -23s
 3 954 tests ±0   3 670 ✅ ±0  284 💤 ±0  0 ❌ ±0 
11 690 runs  ±0  10 805 ✅ ±0  885 💤 ±0  0 ❌ ±0 

Results for commit 067380a. ± Comparison against base commit fb29be9.

♻️ This comment has been updated with latest results.

[tmssngr]

Do you have a snippet to quickly test-drive it before and later? What about the different join- and cap-styles?

[DieterMai]

I will create a test for this

[DieterMai]

I still want to implement some kind of example to better test this drawing operation. But you can also use Snippet 252 with some minor changes to see the issue

public class Snippet252 {

	public static void main(String[] args) {
		final Display display = new Display();
		final Shell shell = new Shell(display);
		shell.setText("Snippet 252");

		SWT.USE_SKIJA = true;
		shell.addListener(SWT.Paint, event -> {
			Drawing.drawWithGC(shell, event.gc, gc -> {
				gc.setLineAttributes(new LineAttributes(10, SWT.CAP_FLAT, SWT.JOIN_MITER, SWT.LINE_SOLID, null, 0, 10));
				gc.drawPolyline(new int[]{50, 100, 50, 20, 60, 30, 50, 45});

				gc.setLineAttributes(new LineAttributes(1/2f, SWT.CAP_FLAT, SWT.JOIN_MITER, SWT.LINE_DOT, null, 0, 10));
				gc.drawPolyline(new int[]{100, 100, 100, 20, 110, 30, 100, 45});
			});

		});

		shell.setSize(150, 150);
		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch()) display.sleep();
		}
		display.dispose();
	}
}

[DieterMai]

I converted this to draft because this is more buggy then i thought.

The methods drawPolygon and fillPolygon are also not correct.

What the skija implementation does is it takes pairs of 3 points and draws triangles. Meaning if skija gets 6 points it will just draw 2 triangles.

[DieterMai]

Reimplemented skijas drawPolyline, drawPolygon, and fillPolygon.

The fillPolygon function still behaves different in some cases but it is a lot closer to what the previous implementation did.

2 other changes

• I had to fix a small bug in ToolItem. The selection values has to be set before notifying listeners.
• I implemented a test stand for the polyline related function. The existing graphics example is not sufficient to test this. If this is too much, i can remove it. It's just for testing.

[tmssngr]

Thanks for the "Polyline teststand". It reveals a couple of bugs in SWT:

• Line Cap, Line Join and Line Style do not have any influence yet
• on my 4k display (175% zoom) clicking in the draw area seems to half the relative point coordinates
  

It looks like you've detected it while working on the Tree implementation. Do you need it for drawing the expansion/collapse triangles? For all horizonal/vertical lines I'd use fillRect with width or height set to 1.

[DieterMai]

• on my 4k display (175% zoom) clicking in the draw area seems to half the relative point coordinates

Is this also the case for the native GC implementation?

It looks like you've detected it while working on the Tree implementation. Do you need it for drawing the expansion/collapse triangles? For all horizontal/vertical lines I'd use fillRect with width or height set to 1.

Yes, i detected it while working on the expanse/collapse symbols. But it is not a blocker. I just encountered it while on it.

[tmssngr]

Is this also the case for the native GC implementation?

No, with native GC this is as expected. It looks like SkijaGC.toOpenPath lacks the DPIUtil.autoScaleUp.