subtract overflow → Infinite loop

[NathanRoyer]

Hi, I was looking for a crate with which I could render SVG commands cpu-side, and I'm very satisfied with the performance of zeno, also with the fact that it has no dependency to other crates.

However, I encountered a problem in one specific configuration.
I'm drawing circles using successive calls to line_to (which is not not the canonical way, one would normally use arc).
When drawing a circle of radius 40px on a 2000x2000 canvas centered at 1500x500, the program:

• panics when built with the debug profile
• loops infinitely when built with the release profile

The panic says attempt to subtract with overflow @ zeno-0.2.2/src/raster.rs:285:18

Using GDB, I was able to determine that sin_half is the first f32 to become NaN, then the NaNs propagate in the following computations. I am not sure which loop never ends exactly.

Here is a minimal reproduction of my code which is enough to trigger the bug on my machine:

use zeno::PathBuilder;
use zeno::Vector;
use zeno::Stroke;
use zeno::Mask;

use std::f32::consts::TAU;

fn main() {
	let w = 2000;
	let h = 2000;
	let mut zeno_path = Vec::new();
	let center = Vector::new(1500.0, 500.0);
	let radius: f32 = 40.0;
	// steps is complex to compute in my real code,
	// so I just put it that way to be sure of its value
	let steps = f32::from_be_bytes([67, 123, 0, 0]); // ~251
	let a_delta = TAU / steps;
	// angle which will go from 0 to TAU
	let mut a: f32 = 0.0;
	let p = |a: f32| {
		let (y, x) = a.sin_cos();
		Vector::new(center.x + x * radius, center.y + y * radius)
	};
	zeno_path.move_to(p(a));
	while a < TAU {
		a += a_delta;
		zeno_path.line_to(p(a));
	}
	zeno_path.close();
	let mut zeno_mask = Mask::new(&zeno_path);
	zeno_mask.size(w, h);
	zeno_mask.style(Stroke::new(10.0));
	let mut buffer = vec![0; (w * h) as usize];
	// infinite loop w/ release and crash with debug:
	zeno_mask.render_into(&mut buffer, None);
}

I'm currently figuring out the way Segments work to eventually figure out a solution to this problem; if you have clues or thoughts about this, please let me know.

[NathanRoyer]

I was not able to fix the bug, however I found a workaround: setting zeno::Join::Bevel via the join setter on a Stroke object prevents the buggy code to run.

[markusmoenig]

Sadly it seems they have abandoned this project.