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Don't give up so quickly when performing Newton-Raphson

This commit is contained in:
Patrick Walton 2017-07-03 20:25:55 -04:00
parent 5393f63738
commit 410d2aa6cd
2 changed files with 8 additions and 10 deletions
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12
partitionfinder/src/geometry.rs
View File

@ -83,17 +83,17 @@ pub fn solve_line_y_for_x(x: f32, a: &Point2D<f32>, b: &Point2D<f32>) -> f32 {
a.lerp(*b, (x - a.x) / (b.x - a.x)).y
}
fn newton_raphson<F, DFDX>(f: F, dfdx: DFDX, mut x_guess: f32) -> Option<f32>
fn newton_raphson<F, DFDX>(f: F, dfdx: DFDX, mut x_guess: f32) -> f32
where F: Fn(f32) -> f32, DFDX: Fn(f32) -> f32 {
for _ in 0..NEWTON_RAPHSON_ITERATIONS {
let y = f(x_guess);
if y.approx_eq(&0.0) {
return Some(x_guess)
break
}
let yy = dfdx(x_guess);
x_guess -= y / yy
}
None
x_guess
}
pub fn solve_cubic_bezier_t_for_x(x: f32,
@ -101,7 +101,7 @@ pub fn solve_cubic_bezier_t_for_x(x: f32,
p1: &Point2D<f32>,
p2: &Point2D<f32>,
p3: &Point2D<f32>)
-> Option<f32> {
-> f32 {
newton_raphson(|t| sample_cubic_bezier(t, p0, p1, p2, p3).x - x,
|t| sample_cubic_bezier_deriv(t, p0, p1, p2, p3).x,
0.5)
@ -112,6 +112,6 @@ pub fn solve_cubic_bezier_y_for_x(x: f32,
p1: &Point2D<f32>,
p2: &Point2D<f32>,
p3: &Point2D<f32>)
-> Option<f32> {
solve_cubic_bezier_t_for_x(x, p0, p1, p2, p3).map(|t| sample_cubic_bezier(t, p0, p1, p2, p3).y)
-> f32 {
sample_cubic_bezier(solve_cubic_bezier_t_for_x(x, p0, p1, p2, p3), p0, p1, p2, p3).y
}

6
partitionfinder/src/partitioner.rs
View File

@ -369,13 +369,12 @@ impl<'a> Partitioner<'a> {
(x - prev_endpoint.position.x) / x_vector
}
Some(control_points_index) => {
// FIXME(pcwalton): Is `unwrap_or(0.0)` sensible?
let control_points = &self.control_points[control_points_index as usize];
geometry::solve_cubic_bezier_t_for_x(x,
&prev_endpoint.position,
&control_points.point1,
&control_points.point2,
&next_endpoint.position).unwrap_or(0.0)
&next_endpoint.position)
}
}
}
@ -414,12 +413,11 @@ impl<'a> Partitioner<'a> {
let control_points_index = self.control_points_index(next_endpoint_index)
.expect("Edge not a cubic bezier!");
let control_points = &self.control_points[control_points_index as usize];
// FIXME(pcwalton): Is `.unwrap_or(0.0)` sensible?
geometry::solve_cubic_bezier_y_for_x(x,
&prev_endpoint.position,
&control_points.point1,
&control_points.point2,
&next_endpoint.position).unwrap_or(0.0)
&next_endpoint.position)
}
fn control_points_index(&self, next_endpoint_index: u32) -> Option<u32> {