gpui: Add move_to method to Path

[huacnlee]

Release Notes:

• N/A

---

Continue #20499

We need this to draw Path. Before this change, we only have line_to, but it is not enough.

Show case

To draw a stroke line is not just to line_to, there need to consider the angle to get shift to draw next point. GPUI have not yet provided this things, but the 3rd-library are have.

For example use tiny-skia:

cargo run -p gpui --example painting

Before version:

[huacnlee]

Also see JakkuSakura/plotters-gpui#2

Previously, GPUI's Path did not have some algorithms for stroke, so we needed to do some complex calculations ourselves. As shown in the figure above, the calculations were actually wrong, and the lines in some directions were not drawn correctly.

For example the plotters-gpui do stroke like by:

https://github.com/JakkuSakura/plotters-gpui/blob/ac70ae70889e8a5f9c7880e826243a23c232c74e/src/line.rs#L55-L76

let (Some(first), Some(last)) = (self.points.first().copied(), self.points.last().copied())
else {
    return;
};

let mut angle = f32::atan2(first.y.0 - last.y.0, first.x.0 - last.x.0);
angle += std::f32::consts::FRAC_PI_2;
let shift = point(width * f32::cos(angle), width * f32::sin(angle));

let mut reversed_points = vec![first + shift];
let mut path = Path::new(first);
for &p in &self.points[1..] {
    path.line_to(p);
    reversed_points.push(p + shift);
}

// now do the reverse to close the path
for p in reversed_points.into_iter().rev() {
    path.line_to(p);
}

cx.paint_path(path, self.color);

If we can introduce something like tiny-skia, relying on the algorithms they provide, we can simplify this process.

The new version by tiny-skia:

Of course, this is actually two things. First, GPUI's Path lacks move_to, which can easily correspond to other vector graphics, such as SVG Path.

cc @JakkuSakura

[huacnlee]

After this merged, the next thing we can push to enable anti-aliasing.

Recently Blade have this support: kvark/blade#213, cc @kvark

[JakkuSakura]

Thanks for pointing out. The algorithm was written so for lacking such stroking algo and for performance consideration

[Angelk90]

@huacnlee and @JakkuSakura : If we wanted to animate a graph showing the performance of a program, how much of an impact would it have on the RAM usage? Would the animation require a significant amount of resources, and could it impact the overall performance of the system?

Registrazione.schermo.2025-01-08.alle.09.33.56.mov

[huacnlee]

@huacnlee and @JakkuSakura : If we wanted to animate a graph showing the performance of a program, how much of an impact would it have on the RAM usage? Would the animation require a significant amount of resources, and could it impact the overall performance of the system?

Registrazione.schermo.2025-01-08.alle.09.33.56.mov

NO! Animate is not have extract RAM, at least not a very noticeable difference.