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Fix floating point error in clipping

This commit is contained in:
Patrick Walton 2019-01-16 20:04:29 -08:00
parent 8166de112c
commit 090e20676a
2 changed files with 38 additions and 33 deletions
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66
geometry/src/clip.rs
View File

@ -8,6 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use crate::line_segment::LineSegmentF32;
use crate::outline::{Contour, PointFlags};
use crate::point::Point2DF32;
use euclid::{Point2D, Rect, Vector3D};
@ -37,11 +38,12 @@ impl<'a> RectClipper<'a> {
}
fn clip_against(&self, edge: Edge, output: &mut Vec<PathEvent>) {
let (mut from, mut path_start, mut first_point) = (Point2D::zero(), None, false);
let (mut from, mut path_start, mut first_point) = (Point2DF32::default(), None, false);
let input = mem::replace(output, vec![]);
for event in input {
let to = match event {
PathEvent::MoveTo(to) => {
let to = Point2DF32::from_euclid(to);
path_start = Some(to);
from = to;
first_point = true;
@ -55,17 +57,19 @@ impl<'a> RectClipper<'a> {
}
PathEvent::LineTo(to) |
PathEvent::QuadraticTo(_, to) |
PathEvent::CubicTo(_, _, to) => to,
PathEvent::CubicTo(_, _, to) => Point2DF32::from_euclid(to),
PathEvent::Arc(..) => panic!("Arcs unsupported!"),
};
if edge.point_is_inside(&to) {
if !edge.point_is_inside(&from) {
add_line(&edge.line_intersection(&from, &to), output, &mut first_point);
let intersection = edge.line_intersection(&LineSegmentF32::new(&from, &to));
add_line(&intersection, output, &mut first_point);
}
add_line(&to, output, &mut first_point);
} else if edge.point_is_inside(&from) {
add_line(&edge.line_intersection(&from, &to), output, &mut first_point);
let intersection = edge.line_intersection(&LineSegmentF32::new(&from, &to));
add_line(&intersection, output, &mut first_point);
}
from = to;
@ -76,12 +80,13 @@ impl<'a> RectClipper<'a> {
}
}
fn add_line(to: &Point2D<f32>, output: &mut Vec<PathEvent>, first_point: &mut bool) {
fn add_line(to: &Point2DF32, output: &mut Vec<PathEvent>, first_point: &mut bool) {
let to = to.as_euclid();
if *first_point {
output.push(PathEvent::MoveTo(*to));
output.push(PathEvent::MoveTo(to));
*first_point = false;
} else {
output.push(PathEvent::LineTo(*to));
output.push(PathEvent::LineTo(to));
}
}
}
@ -96,25 +101,24 @@ enum Edge {
}
impl Edge {
fn point_is_inside(&self, point: &Point2D<f32>) -> bool {
fn point_is_inside(&self, point: &Point2DF32) -> bool {
match *self {
Edge::Left(x_edge) => point.x >= x_edge,
Edge::Top(y_edge) => point.y >= y_edge,
Edge::Right(x_edge) => point.x <= x_edge,
Edge::Bottom(y_edge) => point.y <= y_edge,
Edge::Left(x_edge) => point.x() >= x_edge,
Edge::Top(y_edge) => point.y() >= y_edge,
Edge::Right(x_edge) => point.x() <= x_edge,
Edge::Bottom(y_edge) => point.y() <= y_edge,
}
}
fn line_intersection(&self, start_point: &Point2D<f32>, endpoint: &Point2D<f32>)
-> Point2D<f32> {
let start_point = Vector3D::new(start_point.x, start_point.y, 1.0);
let endpoint = Vector3D::new(endpoint.x, endpoint.y, 1.0);
let edge = match *self {
Edge::Left(x_edge) | Edge::Right(x_edge) => Vector3D::new(1.0, 0.0, -x_edge),
Edge::Top(y_edge) | Edge::Bottom(y_edge) => Vector3D::new(0.0, 1.0, -y_edge),
};
let intersection = start_point.cross(endpoint).cross(edge);
Point2D::new(intersection.x / intersection.z, intersection.y / intersection.z)
fn line_intersection(&self, line_segment: &LineSegmentF32) -> Point2DF32 {
match *self {
Edge::Left(x_edge) | Edge::Right(x_edge) => {
Point2DF32::new(x_edge, line_segment.solve_y_for_x(x_edge))
}
Edge::Top(y_edge) | Edge::Bottom(y_edge) => {
Point2DF32::new(line_segment.solve_x_for_y(y_edge), y_edge)
}
}
}
}
@ -146,21 +150,17 @@ impl ContourRectClipper {
let input = mem::replace(&mut self.contour, Contour::new());
for event in input.iter() {
let (from, to) = (event.baseline.from(), event.baseline.to());
if edge.point_is_inside(&to.as_euclid()) {
if !edge.point_is_inside(&from.as_euclid()) {
if edge.point_is_inside(&to) {
if !edge.point_is_inside(&from) {
//println!("clip: {:?} {:?}", from, to);
add_line(&Point2DF32::from_euclid(edge.line_intersection(&from.as_euclid(),
&to.as_euclid())),
&mut self.contour,
&mut first_point);
let intersection = edge.line_intersection(&LineSegmentF32::new(&from, &to));
add_line(&intersection, &mut self.contour, &mut first_point);
}
add_line(&to, &mut self.contour, &mut first_point);
} else if edge.point_is_inside(&from.as_euclid()) {
} else if edge.point_is_inside(&from) {
//println!("clip: {:?} {:?}", from, to);
add_line(&Point2DF32::from_euclid(edge.line_intersection(&from.as_euclid(),
&to.as_euclid())),
&mut self.contour,
&mut first_point);
let intersection = edge.line_intersection(&LineSegmentF32::new(&from, &to));
add_line(&intersection, &mut self.contour, &mut first_point);
}
}

5
geometry/src/line_segment.rs
View File

@ -113,6 +113,11 @@ impl LineSegmentF32 {
(y - self.from_y()) / (self.to_y() - self.from_y())
}
#[inline]
pub fn solve_x_for_y(&self, y: f32) -> f32 {
util::lerp(self.from_x(), self.to_x(), self.solve_t_for_y(y))
}
#[inline]
pub fn solve_y_for_x(&self, x: f32) -> f32 {
util::lerp(self.from_y(), self.to_y(), self.solve_t_for_x(x))