Glitchy UIBezierPaths when using `fb_union`, `fb_difference` etc functions

[AndrewHartAR]

I'm using the fb_union, fb_difference functions to create a complex bezier path. I'm finding that there are many issues with these functions.

Here is code that generates a rectangle by combining a series of smaller rectangles:

var bezier = UIBezierPath()
	
for x in 20..<30 {
  for y in 15..<20 {
    let rect = CGRect(x: x * 10, y: y * 10, width: 11, height: 11)
    let bezier2 = UIBezierPath(rect: rect)
			
    bezier = bezier.fb_union(bezier2)
  }
}

The width/height is 11 to create a little overlap. From the result I can see that this works, and creates what appears to be a larger rectangle (albeit with a complex single-shape geometry, once printed).

<UIBezierPath: 0x282f98780; <MoveTo {290.49999999999994, 201}>,
 <LineTo {280.49999999999994, 201}>,
 <LineTo {280.49999999999994, 200.99999999999997}>,
 <LineTo {270.50000000000006, 201}>,
 <LineTo {270.49999999999994, 200.99999999999997}>,
 <LineTo {260.50000000000006, 201}>,
 <LineTo {260.49999999999994, 201}>,
 <LineTo {250.5, 201}>,
 <LineTo {250.49999999999994, 201}>,
 <LineTo {240.5, 201}>,
 <LineTo {240.49999999999997, 201}>,
 <LineTo {230.50000000000003, 201}>,
 <LineTo {230.5, 201}>,
 <LineTo {220.50000000000003, 201}>,
 <LineTo {210.50000000000003, 201}>,
 <LineTo {200, 201}>,
 <LineTo {200, 190.50000000000003}>,
 <LineTo {199.99999999999994, 190.50000000000003}>,
 <LineTo {199.99999999999994, 180.5}>,
 <LineTo {200, 170.5}>,
 <LineTo {200, 170.50000000000003}>,
 <LineTo {200, 160.50000000000003}>,
 <LineTo {200, 150}>,
 <LineTo {210.5, 150}>,
 <LineTo {210.50000000000003, 150}>,
 <LineTo {220.49999999999997, 150}>,
 <LineTo {220.50000000000003, 150}>,
 <LineTo {230.50000000000003, 150}>,
 <LineTo {240.50000000000003, 150}>,
 <LineTo {250.50000000000003, 150}>,
 <LineTo {250.5, 150}>,
 <LineTo {260.49999999999994, 150}>,
 <LineTo {260.50000000000006, 150}>,
 <LineTo {270.49999999999994, 150}>,
 <LineTo {270.50000000000006, 150}>,
 <LineTo {280.49999999999994, 150}>,
 <LineTo {280.5, 150}>,
 <LineTo {290.49999999999994, 150}>,
 <LineTo {290.50000000000006, 150}>,
 <LineTo {301, 150}>,
 <LineTo {301, 160.50000000000003}>,
 <LineTo {301, 170.50000000000003}>,
 <LineTo {301, 180.50000000000003}>,
 <LineTo {301, 190.50000000000003}>,
 <LineTo {301, 201}>,
 <LineTo {290.5, 201}>,
 <Close>

Then I remove every other column, by only drawing columns on even rows:

var bezier = UIBezierPath()
	
for x in 20..<30 {
  if floor(Double(x) / 2) != Double(x) / 2 {
    continue
  }

  for y in 15..<20 {
    let rect = CGRect(x: x * 10, y: y * 10, width: 11, height: 11)
    let bezier2 = UIBezierPath(rect: rect)
			
    bezier = bezier.fb_union(bezier2)
  }
}

The result here is that some of the shapes which should be drawn, inexplicably aren't.

This is an example result - I'm only showing issues with fb_union here, but this issue is very prevalent across uses of these functions. This can be tested using the attached sample project.

beziertest.zip

[sabiland]

Is this project still maintained? I noticed today that if:

1. Take UIBezierPath rect (say 1000 x 1000)
2. Take UIBezierPath triangle (exactly half of the rect)
3. I was expecting to get exactly inverted triangle inside the rect

But fb_difference doesn't do anything in this case. It just returns the same triangle as input.

But if I resize rect just a little bit (up or down) then fb_difference works as it should.