pathfinder/path-utils/src/lib.rs

// pathfinder/path-utils/src/lib.rs
//
// Copyright © 2017 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.

extern crate arrayvec;
extern crate euclid;
extern crate freetype_sys;
#[macro_use]
extern crate serde_derive;

use euclid::{Point2D, Transform2D};
use std::u32;

pub mod curve;
pub mod freetype;
pub mod intersection;
pub mod line;
pub mod monotonic;
pub mod stroke;

#[derive(Clone, Copy, Debug)]
pub enum PathSegment {
    MoveTo(Point2D<f32>),
    LineTo(Point2D<f32>),
    CurveTo(Point2D<f32>, Point2D<f32>),
    ClosePath,
}

#[derive(Clone, Debug)]
pub struct PathBuffer {
    pub endpoints: Vec<Endpoint>,
    pub control_points: Vec<Point2D<f32>>,
    pub subpaths: Vec<Subpath>,
}

impl PathBuffer {
    #[inline]
    pub fn new() -> PathBuffer {
        PathBuffer {
            endpoints: vec![],
            control_points: vec![],
            subpaths: vec![],
        }
    }

    pub fn add_stream<I>(&mut self, stream: I) where I: Iterator<Item = PathSegment> {
        let mut first_subpath_endpoint_index = self.endpoints.len() as u32;
        for segment in stream {
            match segment {
                PathSegment::ClosePath => self.close_subpath(&mut first_subpath_endpoint_index),

                PathSegment::MoveTo(position) => {
                    self.close_subpath(&mut first_subpath_endpoint_index);
                    self.endpoints.push(Endpoint {
                        position: position,
                        control_point_index: u32::MAX,
                        subpath_index: self.subpaths.len() as u32,
                    })
                }

                PathSegment::LineTo(position) => {
                    self.endpoints.push(Endpoint {
                        position: position,
                        control_point_index: u32::MAX,
                        subpath_index: self.subpaths.len() as u32,
                    })
                }

                PathSegment::CurveTo(control_point_position, endpoint_position) => {
                    let control_point_index = self.control_points.len() as u32;
                    self.control_points.push(control_point_position);
                    self.endpoints.push(Endpoint {
                        position: endpoint_position,
                        control_point_index: control_point_index,
                        subpath_index: self.subpaths.len() as u32,
                    })
                }
            }
        }

        self.close_subpath(&mut first_subpath_endpoint_index)
    }

    fn close_subpath(&mut self, first_subpath_endpoint_index: &mut u32) {
        let last_subpath_endpoint_index = self.endpoints.len() as u32;
        if *first_subpath_endpoint_index != last_subpath_endpoint_index {
            self.subpaths.push(Subpath {
                first_endpoint_index: *first_subpath_endpoint_index,
                last_endpoint_index: last_subpath_endpoint_index,
            })
        }

        *first_subpath_endpoint_index = last_subpath_endpoint_index;
    }
}

pub struct PathBufferStream<'a> {
    path_buffer: &'a PathBuffer,
    endpoint_index: u32,
    subpath_index: u32,
}

impl<'a> PathBufferStream<'a> {
    pub fn new<'b>(path_buffer: &'b PathBuffer) -> PathBufferStream<'b> {
        PathBufferStream {
            path_buffer: path_buffer,
            endpoint_index: 0,
            subpath_index: 0,
        }
    }
}

impl<'a> Iterator for PathBufferStream<'a> {
    type Item = PathSegment;

    fn next(&mut self) -> Option<PathSegment> {
        if self.subpath_index as usize == self.path_buffer.subpaths.len() {
            return None
        }

        let subpath = &self.path_buffer.subpaths[self.subpath_index as usize];
        if self.endpoint_index == subpath.last_endpoint_index {
            self.subpath_index += 1;
            return Some(PathSegment::ClosePath)
        }

        let endpoint = &self.path_buffer.endpoints[self.endpoint_index as usize];
        self.endpoint_index += 1;

        if self.endpoint_index == subpath.first_endpoint_index {
            return Some(PathSegment::MoveTo(endpoint.position))
        }

        if endpoint.control_point_index == u32::MAX {
            return Some(PathSegment::LineTo(endpoint.position))
        }

        let control_point = &self.path_buffer
                                 .control_points[endpoint.control_point_index as usize];
        Some(PathSegment::CurveTo(*control_point, endpoint.position))
    }
}

#[repr(C)]
#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
pub struct Endpoint {
    pub position: Point2D<f32>,
    /// `u32::MAX` if not present.
    pub control_point_index: u32,
    pub subpath_index: u32,
}

#[repr(C)]
#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
pub struct Subpath {
    pub first_endpoint_index: u32,
    pub last_endpoint_index: u32,
}

pub struct Transform2DPathStream<I> {
    inner: I,
    transform: Transform2D<f32>,
}

impl<I> Transform2DPathStream<I> where I: Iterator<Item = PathSegment> {
    pub fn new(inner: I, transform: &Transform2D<f32>) -> Transform2DPathStream<I> {
        Transform2DPathStream {
            inner: inner,
            transform: *transform,
        }
    }
}

impl<I> Iterator for Transform2DPathStream<I> where I: Iterator<Item = PathSegment> {
    type Item = PathSegment;

    fn next(&mut self) -> Option<PathSegment> {
        match self.inner.next() {
            None => None,
            Some(PathSegment::MoveTo(position)) => {
                Some(PathSegment::MoveTo(self.transform.transform_point(&position)))
            }
            Some(PathSegment::LineTo(position)) => {
                Some(PathSegment::LineTo(self.transform.transform_point(&position)))
            }
            Some(PathSegment::CurveTo(control_point_position, endpoint_position)) => {
                Some(PathSegment::CurveTo(self.transform.transform_point(&control_point_position),
                                          self.transform.transform_point(&endpoint_position)))
            }
            Some(PathSegment::ClosePath) => Some(PathSegment::ClosePath),
        }
    }
}

#[inline]
pub(crate) fn lerp(a: f32, b: f32, t: f32) -> f32 {
    a + (b - a) * t
}

#[inline]
pub(crate) fn det2x2(m: &[f32; 4]) -> f32 {
    m[0] * m[3] - m[1] * m[2]
}

pub(crate) fn det3x3(m: &[f32; 9]) -> f32 {
    m[0] * det2x2(&[m[4], m[5], m[7], m[8]]) -
    m[1] * det2x2(&[m[3], m[5], m[6], m[8]]) +
    m[2] * det2x2(&[m[3], m[4], m[6], m[7]])
}