pathfinder/utils/tile-svg/src/main.rs

// pathfinder/utils/tile-svg/main.rs
//
// Copyright © 2018 The Pathfinder Project Developers.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#[macro_use]
extern crate bitflags;

#[cfg(test)]
extern crate quickcheck;
#[cfg(test)]
extern crate rand;

use euclid::{Point2D, Rect, Transform2D, Vector2D};
use lyon_algorithms::geom::{CubicBezierSegment, LineSegment, QuadraticBezierSegment};
use quick_xml::Reader;
use quick_xml::events::Event;
use std::cmp::Ordering;
use std::env;
use std::mem;
use std::path::{Path, PathBuf};
use std::str::FromStr;
use std::time::Instant;
use svgtypes::{Color as SvgColor, PathParser, PathSegment as SvgPathSegment, TransformListParser};
use svgtypes::{TransformListToken};

#[derive(Default)]
struct GroupStyle {
    fill_color: Option<SvgColor>,
    stroke_width: Option<f32>,
    stroke_color: Option<SvgColor>,
    transform: Option<Transform2D<f32>>,
}

#[derive(Debug)]
struct ComputedStyle {
    fill_color: Option<SvgColor>,
    stroke_width: f32,
    stroke_color: Option<SvgColor>,
    transform: Transform2D<f32>,
}

impl ComputedStyle {
    fn new() -> ComputedStyle {
        ComputedStyle {
            fill_color: None,
            stroke_width: 1.0,
            stroke_color: None,
            transform: Transform2D::identity(),
        }
    }
}

fn main() {
    let path = PathBuf::from(env::args().skip(1).next().unwrap());
    let scene = Scene::from_path(&path);

    const RUNS: u32 = 1000;
    let start_time = Instant::now();
    for _ in 0..RUNS {
        scene.generate_tiles();
    }
    let elapsed_time = Instant::now() - start_time;
    let elapsed_ms = elapsed_time.as_secs() as f64 * 1000.0 +
        elapsed_time.subsec_micros() as f64 / 1000.0;
    println!("{}ms elapsed", elapsed_ms / RUNS as f64);
}

#[derive(Debug)]
struct Scene {
    objects: Vec<PathObject>,
    styles: Vec<ComputedStyle>,
}

#[derive(Debug)]
struct PathObject {
    outline: Outline,
    style: StyleId,
}

#[derive(Clone, Copy, PartialEq, Debug)]
struct StyleId(u32);

impl Scene {
    fn new() -> Scene {
        Scene {
            objects: vec![],
            styles: vec![],
        }
    }

    fn from_path(path: &Path) -> Scene {
        let mut reader = Reader::from_file(&path).unwrap();

        let mut xml_buffer = vec![];
        let mut group_styles = vec![];
        let mut style = None;

        let mut scene = Scene::new();

        loop {
            match reader.read_event(&mut xml_buffer) {
                Ok(Event::Start(ref event)) |
                Ok(Event::Empty(ref event)) if event.name() == b"path" => {
                    let attributes = event.attributes();
                    for attribute in attributes {
                        let attribute = attribute.unwrap();
                        if attribute.key != b"d" {
                            continue
                        }
                        let value = reader.decode(&attribute.value);
                        let style = scene.ensure_style(&mut style, &mut group_styles);
                        let path_parser = PathParser::from(&*value);
                        let outline =
                            Outline::from_svg_path_segments(path_parser, scene.get_style(style));
                        scene.objects.push(PathObject::new(outline, style));
                    }
                }
                Ok(Event::Start(ref event)) if event.name() == b"g" => {
                    let mut group_style = GroupStyle::default();
                    let attributes = event.attributes();
                    for attribute in attributes {
                        let attribute = attribute.unwrap();
                        match attribute.key {
                            b"fill" => {
                                let value = reader.decode(&attribute.value);
                                if let Ok(color) = SvgColor::from_str(&value) {
                                    group_style.fill_color = Some(color)
                                }
                            }
                            b"stroke" => {
                                let value = reader.decode(&attribute.value);
                                if let Ok(color) = SvgColor::from_str(&value) {
                                    group_style.stroke_color = Some(color)
                                }
                            }
                            b"transform" => {
                                let value = reader.decode(&attribute.value);
                                let mut current_transform = Transform2D::identity();
                                let transform_list_parser = TransformListParser::from(&*value);
                                for transform in transform_list_parser {
                                    match transform {
                                        Ok(TransformListToken::Matrix { a, b, c, d, e, f }) => {
                                            let transform: Transform2D<f32> =
                                                Transform2D::row_major(a, b, c, d, e, f).cast();
                                            current_transform = current_transform.pre_mul(&transform)
                                        }
                                        _ => {}
                                    }
                                }
                                group_style.transform = Some(current_transform);
                            }
                            b"stroke-width" => {
                                if let Ok(width) = reader.decode(&attribute.value).parse() {
                                    group_style.stroke_width = Some(width)
                                }
                            }
                            _ => {}
                        }
                    }
                    group_styles.push(group_style);
                    style = None;
                }
                Ok(Event::Eof) | Err(_) => break,
                Ok(_) => {}
            }
            xml_buffer.clear();
        }

        return scene;

    }

    fn ensure_style(&mut self, current_style: &mut Option<StyleId>, group_styles: &[GroupStyle])
                    -> StyleId {
        if let Some(current_style) = *current_style {
            return current_style
        }

        let mut computed_style = ComputedStyle::new();
        for group_style in group_styles {
            if let Some(fill_color) = group_style.fill_color {
                computed_style.fill_color = Some(fill_color)
            }
            if let Some(stroke_width) = group_style.stroke_width {
                computed_style.stroke_width = stroke_width
            }
            if let Some(stroke_color) = group_style.stroke_color {
                computed_style.stroke_color = Some(stroke_color)
            }
            if let Some(transform) = group_style.transform {
                computed_style.transform = computed_style.transform.pre_mul(&transform)
            }
        }

        let id = StyleId(self.styles.len() as u32);
        self.styles.push(computed_style);
        id
    }

    fn get_style(&self, style: StyleId) -> &ComputedStyle {
        &self.styles[style.0 as usize]
    }

    fn generate_tiles(&self) {
        let mut strips = vec![];
        for object in &self.objects {
            let mut tiler = Tiler::from_outline(&object.outline);
            tiler.generate_tiles(&mut strips);
            // TODO(pcwalton)
        }
    }
}

impl PathObject {
    fn new(outline: Outline, style: StyleId) -> PathObject {
        PathObject {
            outline,
            style,
        }
    }
}

// Outlines

#[derive(Debug)]
struct Outline {
    contours: Vec<Contour>,
    bounds: Rect<f32>,
}

#[derive(Debug)]
struct Contour {
    points: Vec<Point2D<f32>>,
    flags: Vec<PointFlags>,
}

bitflags! {
    struct PointFlags: u8 {
        const CONTROL_POINT_0 = 0x01;
        const CONTROL_POINT_1 = 0x02;
    }
}

impl Outline {
    fn new() -> Outline {
        Outline {
            contours: vec![],
            bounds: Rect::zero(),
        }
    }

    fn from_svg_path_segments<I>(segments: I, style: &ComputedStyle) -> Outline
                                 where I: Iterator<Item = SvgPathSegment> {
        let mut outline = Outline::new();
        let mut current_contour = Contour::new();
        let mut bounding_points = None;
        let (mut first_point_in_path, mut last_ctrl_point, mut last_point) = (None, None, None);

        for segment in segments {
            match segment {
                SvgPathSegment::MoveTo { abs, x, y } => {
                    if !current_contour.is_empty() {
                        outline.contours.push(mem::replace(&mut current_contour, Contour::new()))
                    }
                    let to = compute_point(x, y, abs, &last_point);
                    first_point_in_path = Some(to);
                    last_point = Some(to);
                    last_ctrl_point = None;
                    current_contour.push_transformed_point(&to,
                                                           PointFlags::empty(),
                                                           &style.transform,
                                                           &mut bounding_points);
                }
                SvgPathSegment::LineTo { abs, x, y } => {
                    let to = compute_point(x, y, abs, &last_point);
                    last_point = Some(to);
                    last_ctrl_point = None;
                    current_contour.push_transformed_point(&to,
                                                           PointFlags::empty(),
                                                           &style.transform,
                                                           &mut bounding_points);
                }
                SvgPathSegment::HorizontalLineTo { abs, x } => {
                    let to = Point2D::new(compute_point(x, 0.0, abs, &last_point).x,
                                          last_point.unwrap_or(Point2D::zero()).y);
                    last_point = Some(to);
                    last_ctrl_point = None;
                    current_contour.push_transformed_point(&to,
                                                           PointFlags::empty(),
                                                           &style.transform,
                                                           &mut bounding_points);
                }
                SvgPathSegment::VerticalLineTo { abs, y } => {
                    let to = Point2D::new(last_point.unwrap_or(Point2D::zero()).x,
                                          compute_point(0.0, y, abs, &last_point).y);
                    last_point = Some(to);
                    last_ctrl_point = None;
                    current_contour.push_transformed_point(&to,
                                                           PointFlags::empty(),
                                                           &style.transform,
                                                           &mut bounding_points);
                }
                SvgPathSegment::Quadratic { abs, x1, y1, x, y } => {
                    let ctrl = compute_point(x1, y1, abs, &last_point);
                    last_ctrl_point = Some(ctrl);
                    let to = compute_point(x, y, abs, &last_point);
                    last_point = Some(to);
                    current_contour.push_transformed_point(&ctrl,
                                                           PointFlags::CONTROL_POINT_0,
                                                           &style.transform,
                                                           &mut bounding_points);
                    current_contour.push_transformed_point(&to,
                                                           PointFlags::empty(),
                                                           &style.transform,
                                                           &mut bounding_points);
                }
                SvgPathSegment::SmoothQuadratic { abs, x, y } => {
                    let ctrl = last_point.unwrap_or(Point2D::zero()) +
                        (last_point.unwrap_or(Point2D::zero()) -
                         last_ctrl_point.unwrap_or(Point2D::zero()));
                    last_ctrl_point = Some(ctrl);
                    let to = compute_point(x, y, abs, &last_point);
                    last_point = Some(to);
                    current_contour.push_transformed_point(&ctrl,
                                                           PointFlags::CONTROL_POINT_0,
                                                           &style.transform,
                                                           &mut bounding_points);
                    current_contour.push_transformed_point(&to,
                                                           PointFlags::empty(),
                                                           &style.transform,
                                                           &mut bounding_points);
                }
                SvgPathSegment::CurveTo { abs, x1, y1, x2, y2, x, y } => {
                    let ctrl0 = compute_point(x1, y1, abs, &last_point);
                    let ctrl1 = compute_point(x2, y2, abs, &last_point);
                    last_ctrl_point = Some(ctrl1);
                    let to = compute_point(x, y, abs, &last_point);
                    last_point = Some(to);
                    current_contour.push_transformed_point(&ctrl0,
                                                           PointFlags::CONTROL_POINT_0,
                                                           &style.transform,
                                                           &mut bounding_points);
                    current_contour.push_transformed_point(&ctrl1,
                                                           PointFlags::CONTROL_POINT_1,
                                                           &style.transform,
                                                           &mut bounding_points);
                    current_contour.push_transformed_point(&to,
                                                           PointFlags::empty(),
                                                           &style.transform,
                                                           &mut bounding_points);
                }
                SvgPathSegment::SmoothCurveTo { abs, x2, y2, x, y } => {
                    let ctrl0 = last_point.unwrap_or(Point2D::zero()) +
                        (last_point.unwrap_or(Point2D::zero()) -
                         last_ctrl_point.unwrap_or(Point2D::zero()));
                    let ctrl1 = compute_point(x2, y2, abs, &last_point);
                    last_ctrl_point = Some(ctrl1);
                    let to = compute_point(x, y, abs, &last_point);
                    last_point = Some(to);
                    current_contour.push_transformed_point(&ctrl0,
                                                           PointFlags::CONTROL_POINT_0,
                                                           &style.transform,
                                                           &mut bounding_points);
                    current_contour.push_transformed_point(&ctrl1,
                                                           PointFlags::CONTROL_POINT_1,
                                                           &style.transform,
                                                           &mut bounding_points);
                    current_contour.push_transformed_point(&to,
                                                           PointFlags::empty(),
                                                           &style.transform,
                                                           &mut bounding_points);
                }
                SvgPathSegment::ClosePath { abs: _ } => {
                    if !current_contour.is_empty() {
                        outline.contours.push(mem::replace(&mut current_contour, Contour::new()));
                        last_point = first_point_in_path;
                        last_ctrl_point = None;
                    }
                }
                SvgPathSegment::EllipticalArc { .. } => unimplemented!("arcs"),
            }
        }
        if !current_contour.is_empty() {
            outline.contours.push(current_contour)
        }

        if let Some((upper_left, lower_right)) = bounding_points {
            outline.bounds = Rect::from_points([upper_left, lower_right].into_iter())
        }

        return outline;

        fn compute_point(x: f64, y: f64, abs: bool, last_point: &Option<Point2D<f32>>)
                         -> Point2D<f32> {
            let point = Point2D::new(x, y).to_f32();
            match *last_point {
                Some(last_point) if !abs => last_point + point.to_vector(),
                _ => point,
            }
        }
    }

    fn segment_after(&self, endpoint_index: PointIndex) -> Segment {
        self.contours[endpoint_index.contour_index].segment_after(endpoint_index.point_index)
    }
}

impl Contour {
    fn new() -> Contour {
        Contour {
            points: vec![],
            flags: vec![],
        }
    }

    fn is_empty(&self) -> bool {
        self.points.is_empty()
    }

    fn push_transformed_point(&mut self,
                              point: &Point2D<f32>,
                              flags: PointFlags,
                              transform: &Transform2D<f32>,
                              bounding_points: &mut Option<(Point2D<f32>, Point2D<f32>)>) {
        let point = transform.transform_point(point);
        self.points.push(point);
        self.flags.push(flags);

        match *bounding_points {
            Some((ref mut upper_left, ref mut lower_right)) => {
                *upper_left = upper_left.min(point);
                *lower_right = lower_right.max(point);
            }
            None => *bounding_points = Some((point, point)),
        }
    }

    fn segment_after(&self, point_index: usize) -> Segment {
        debug_assert!(self.point_is_endpoint(point_index));
        let point1_index = self.add_to_point_index(point_index, 1);
        if self.point_is_endpoint(point1_index) {
            return Segment::Line(LineSegment {
                from: self.points[point_index],
                to: self.points[point1_index],
            })
        }
        let point2_index = self.add_to_point_index(point_index, 2);
        if self.point_is_endpoint(point2_index) {
            return Segment::Quadratic(QuadraticBezierSegment {
                from: self.points[point_index],
                ctrl: self.points[point1_index],
                to: self.points[point2_index],
            })
        }
        let point3_index = self.add_to_point_index(point_index, 3);
        Segment::Cubic(CubicBezierSegment {
            from: self.points[point_index],
            ctrl1: self.points[point1_index],
            ctrl2: self.points[point2_index],
            to: self.points[point3_index],
        })
    }

    fn point_is_endpoint(&self, point_index: usize) -> bool {
        self.flags[point_index].intersects(PointFlags::CONTROL_POINT_0 |
                                           PointFlags::CONTROL_POINT_1)
    }

    fn add_to_point_index(&self, point_index: usize, addend: usize) -> usize {
        (point_index + addend) % self.points.len()
    }
}

#[derive(Clone, Copy, Debug)]
struct PointIndex {
    contour_index: usize,
    point_index: usize,
}

#[derive(Clone, Copy, Debug, PartialEq)]
enum Segment {
    None,
    Line(LineSegment<f32>),
    Quadratic(QuadraticBezierSegment<f32>),
    Cubic(CubicBezierSegment<f32>),
}

impl Segment {
    fn is_none(&self) -> bool {
        match *self {
            Segment::None => true,
            _ => false,
        }
    }

    fn endpoints(&self) -> (Point2D<f32>, Point2D<f32>) {
        match *self {
            Segment::Line(ref line) => (line.from, line.to),
            Segment::Quadratic(ref curve) => (curve.from, curve.to),
            Segment::Cubic(ref curve) => (curve.from, curve.to),
            Segment::None => unreachable!(),
        }
    }

    // Note: If we convert these to monotonic then we can optimize this method.
    // TODO(pcwalton): Consider changing the representation of `Segment` to remove the code
    // duplication in the branches here?
    fn min_y(&self) -> f32 {
        match *self {
            Segment::Line(ref line) => f32::min(line.from.y, line.to.y),
            Segment::Quadratic(ref curve) => {
                f32::min(f32::min(curve.from.y, curve.ctrl.y), curve.to.y)
            }
            Segment::Cubic(ref curve) => {
                f32::min(f32::min(f32::min(curve.from.y, curve.ctrl1.y), curve.ctrl2.y),
                         curve.to.y)
            }
            Segment::None => unreachable!(),
        }
    }

    fn clip_y(&self, y: f32) -> ClippedSegments {
        let (from, to) = self.endpoints();
        if from.y < y && to.y < y {
            return ClippedSegments { min: Some(*self), max: None }
        }
        if from.y > y && to.y > y {
            return ClippedSegments { min: None, max: Some(*self) }
        }

        let (prev, next) = match *self {
            Segment::Line(ref line) => {
                let (prev, next) = line.split(line.solve_t_for_y(y));
                (Segment::Line(prev), Segment::Line(next))
            }
            Segment::Quadratic(ref curve) => {
                let (prev, next) = curve.split(curve.assume_monotonic().solve_t_for_y(y));
                (Segment::Quadratic(prev), Segment::Quadratic(next))
            }
            Segment::Cubic(ref curve) => {
                let swapped_curve = CubicBezierSegment {
                    from: curve.from.yx(),
                    ctrl1: curve.ctrl1.yx(),
                    ctrl2: curve.ctrl2.yx(),
                    to: curve.to.yx(),
                };
                let (prev, next) = curve.split(
                        swapped_curve.assume_monotonic().solve_t_for_x(y, 0.0..1.0, TOLERANCE));
                (Segment::Cubic(prev), Segment::Cubic(next))
            }
            Segment::None => unreachable!(),
        };

        if from.y <= to.y {
            return ClippedSegments { min: Some(prev), max: Some(next) };
        } else {
            return ClippedSegments { min: Some(next), max: Some(prev) };
        }

        const TOLERANCE: f32 = 0.01;
    }

    fn translate(&self, by: &Vector2D<f32>) -> Segment {
        match *self {
            Segment::Line(ref line) => {
                Segment::Line(LineSegment {
                    from: line.from + *by,
                    to: line.to + *by,
                })
            }
            Segment::Quadratic(ref curve) => {
                Segment::Quadratic(QuadraticBezierSegment {
                    from: curve.from + *by,
                    ctrl: curve.ctrl + *by,
                    to: curve.to + *by,
                })
            }
            Segment::Cubic(ref curve) => {
                Segment::Cubic(CubicBezierSegment {
                    from: curve.from + *by,
                    ctrl1: curve.ctrl1 + *by,
                    ctrl2: curve.ctrl2 + *by,
                    to: curve.to + *by,
                })
            }
            Segment::None => unreachable!(),
        }
    }
}

struct ClippedSegments {
    min: Option<Segment>,
    max: Option<Segment>,
}

// Tiling

const TILE_WIDTH: f32 = 4.0;
const TILE_HEIGHT: f32 = 4.0;

struct Tiler<'a> {
    outline: &'a Outline,

    sorted_edge_indices: Vec<PointIndex>,
    active_intervals: Intervals,
    active_edges: Vec<Segment>,
}

impl<'a> Tiler<'a> {
    fn from_outline(outline: &Outline) -> Tiler {
        Tiler {
            outline,

            sorted_edge_indices: vec![],
            active_intervals: Intervals::new(0.0),
            active_edges: vec![],
        }
    }

    fn generate_tiles(&mut self, strips: &mut Vec<Strip>) {
        // Sort all edge indices.
        self.sorted_edge_indices.clear();
        for contour_index in 0..self.outline.contours.len() {
            let contour = &self.outline.contours[contour_index];
            for point_index in 0..contour.points.len() {
                if contour.point_is_endpoint(point_index) {
                    self.sorted_edge_indices.push(PointIndex { contour_index, point_index })
                }
            }
        }
        {
            let outline = &self.outline;
            self.sorted_edge_indices.sort_by(|edge_index_a, edge_index_b| {
                let segment_a = outline.segment_after(*edge_index_a);
                let segment_b = outline.segment_after(*edge_index_b);
                segment_a.min_y().partial_cmp(&segment_b.min_y()).unwrap_or(Ordering::Equal)
            });
        }

        let bounds = self.outline.bounds;
        let (max_x, max_y) = (bounds.max_x(), bounds.max_y());

        self.active_intervals.reset(max_x);
        self.active_edges.clear();
        let mut next_edge_index_index = 0;

        let mut tile_top = bounds.origin.y - bounds.origin.y % TILE_HEIGHT;
        while tile_top < max_y {
            let mut strip = Strip::new(tile_top);

            // TODO(pcwalton): Populate tile strip with active intervals.

            for active_edge in &mut self.active_edges {
                process_active_edge(active_edge, &mut strip, &mut self.active_intervals)
            }
            self.active_edges.retain(|edge| !edge.is_none());

            while next_edge_index_index < self.sorted_edge_indices.len() {
                let mut segment =
                    self.outline.segment_after(self.sorted_edge_indices[next_edge_index_index]);
                if segment.min_y() > strip.tile_bottom() {
                    break
                }

                process_active_edge(&mut segment, &mut strip, &mut self.active_intervals);
                if !segment.is_none() {
                    self.active_edges.push(segment);
                }

                next_edge_index_index += 1;
            }

            tile_top = strip.tile_bottom();
            strips.push(strip);
        }
    }
}

fn process_active_edge(active_edge: &mut Segment,
                       strip: &mut Strip,
                       active_intervals: &mut Intervals) {
    let clipped = active_edge.clip_y(strip.tile_bottom());
    if let Some(upper_segment) = clipped.min {
        strip.push_segment(upper_segment);
        // FIXME(pcwalton): Assumes x-monotonicity!
        // FIXME(pcwalton): The min call below is a hack!
        let (from, to) = upper_segment.endpoints();
        let from_x = f32::max(0.0, f32::min(active_intervals.extent(), from.x));
        let to_x = f32::max(0.0, f32::min(active_intervals.extent(), to.x));
        if from_x < to_x {
            active_intervals.add(IntervalRange::new(from_x, to_x, -1.0))
        } else {
            active_intervals.add(IntervalRange::new(to_x, from_x, 1.0))
        }
    }

    match clipped.max {
        Some(lower_segment) => *active_edge = lower_segment,
        None => *active_edge = Segment::None,
    }
}

// Strips

struct Strip {
    segments: Vec<Segment>,
    tile_top: f32,
}

impl Strip {
    fn new(tile_top: f32) -> Strip {
        Strip {
            segments: vec![],
            tile_top,
        }
    }

    fn push_segment(&mut self, segment: Segment) {
        self.segments.push(segment.translate(&Vector2D::new(0.0, -self.tile_top)))
    }

    fn tile_bottom(&self) -> f32 {
        self.tile_top + TILE_HEIGHT
    }
}

// Intervals

#[derive(Debug)]
struct Intervals {
    ranges: Vec<IntervalRange>,
}

#[derive(Clone, Copy, Debug)]
struct IntervalRange {
    start: f32,
    end: f32,
    winding: f32,
}

impl Intervals {
    fn new(end: f32) -> Intervals {
        Intervals {
            ranges: vec![IntervalRange::new(0.0, end, 0.0)],
        }
    }

    fn add(&mut self, range: IntervalRange) {
        self.split_at(range.start);
        self.split_at(range.end);

        // Find bracketing range.
        let mut start_index = 0;
        while range.start < self.ranges[start_index].start {
            start_index += 1
        }
        let mut end_index = start_index;
        while range.end < self.ranges[end_index].end {
            end_index += 1
        }

        // Adjust winding numbers.
        for existing_range in &mut self.ranges[start_index..(end_index + 1)] {
            existing_range.winding += range.winding
        }

        self.merge_adjacent();
    }

    fn reset(&mut self, end: f32) {
        self.ranges.truncate(1);
        self.ranges[0] = IntervalRange::new(0.0, end, 0.0);
    }

    fn extent(&self) -> f32 {
        self.ranges.last().unwrap().end
    }

    fn split_at(&mut self, value: f32) {
        let mut range_index = 0;
        while range_index < self.ranges.len() {
            let IntervalRange {
                start: old_start,
                end: old_end,
                winding,
            } = self.ranges[range_index];
            if value < old_start || value > old_end {
                range_index += 1;
                continue
            }

            self.ranges[range_index] = IntervalRange::new(old_start, value, winding);
            self.ranges.insert(range_index + 1, IntervalRange::new(value, old_end, winding));
            return
        }
    }

    fn merge_adjacent(&mut self) {
        let mut dest_range_index = 0;
        let mut current_range = self.ranges[0];
        for src_range_index in 1..self.ranges.len() {
            if self.ranges[src_range_index].winding == current_range.winding {
                current_range.end = self.ranges[src_range_index].end
            } else {
                self.ranges[dest_range_index] = current_range;
                dest_range_index += 1;
                current_range = self.ranges[src_range_index];
            }
        }
        self.ranges[dest_range_index] = current_range;
        dest_range_index += 1;
        self.ranges.truncate(dest_range_index);
    }
}

impl IntervalRange {
    fn new(start: f32, end: f32, winding: f32) -> IntervalRange {
        IntervalRange {
            start,
            end,
            winding,
        }
    }

    fn contains(&self, value: f32) -> bool {
        value >= self.start && value < self.end
    }
}

#[cfg(test)]
mod test {
    use crate::{IntervalRange, Intervals};
    use quickcheck::{self, Arbitrary, Gen};
    use rand::Rng;

    #[test]
    fn test_intervals() {
        quickcheck::quickcheck(prop_intervals as fn(Spec) -> bool);

        fn prop_intervals(spec: Spec) -> bool {
            let mut intervals = Intervals::new(spec.end);
            for range in spec.ranges {
                intervals.add(range);
            }

            assert!(intervals.ranges.len() > 0);
            assert_eq!(intervals.ranges[0].start, 0.0);
            assert_eq!(intervals.ranges.last().unwrap().end, spec.end);
            for prev_index in 0..(intervals.ranges.len() - 1) {
                let next_index = prev_index + 1;
                assert_eq!(intervals.ranges[prev_index].end, intervals.ranges[next_index].start);
                assert_ne!(intervals.ranges[prev_index].winding,
                           intervals.ranges[next_index].winding);
            }

            true
        }

        #[derive(Clone, Debug)]
        struct Spec {
            end: f32,
            ranges: Vec<IntervalRange>,
        }

        impl Arbitrary for Spec {
            fn arbitrary<G>(g: &mut G) -> Spec where G: Gen {
                const EPSILON: f32 = 0.0001;

                let size = g.size();
                let end = g.gen_range(EPSILON, size as f32);

                let mut ranges = vec![];
                let range_count = g.gen_range(0, size);
                for _ in 0..range_count {
                    let (a, b) = (g.gen_range(0.0, end), g.gen_range(0.0, end));
                    let winding = g.gen_range(-(size as i32), size as i32) as f32;
                    ranges.push(IntervalRange::new(f32::min(a, b), f32::max(a, b), winding));
                }

                Spec {
                    end,
                    ranges,
                }
            }
        }
    }
}