clipline

Efficient rasterization of line segments with pixel-perfect clipping.

Overview

• Provides iterators for clipped and unclipped rasterized line segments.
  • Eliminates bounds checking: clipped line segments are guaranteed to be within the region.
  • Guarantees clipped line segments match the unclipped versions of themselves.
• Supports signed and unsigned integer coordinates of most sizes.
  • Uses integer arithmetic only.
  • Prevents overflow and division by zero, forbids clippy::arithmetic_side_effects.
  • Defines the iterators on the entire domains of the underlying numeric types.
• Usable in const contexts and #![no_std] environments.

Usage

Add clipline to Cargo.toml:

[dependencies]
clipline = "0.3.0"

Feature flags

• octant_64
  • Enables Octant and AnyOctant over i64/u64 for all targets, and over isize/usize for 64-bit targets.
  • Use this only if you need the full 64-bit range, as Octant will use u128 and i128 for some calculations.
• try_fold, is_empty (nightly-only)
  • Enable optimized Iterator::try_fold and ExactSizeIterator::is_empty implementations.

Example

use clipline::{AnyOctant, Clip, Diagonal0, Point};

/// Width of the pixel buffer.
const WIDTH: usize = 64;
/// Height of the pixel buffer.
const HEIGHT: usize = 48;

/// Pixel color value.
const RGBA: u32 = 0xFFFFFFFF;

/// A function that operates on a single pixel in a pixel buffer.
///
/// ## Safety
/// `(x, y)` must be inside the `buffer`.
unsafe fn draw(buffer: &mut [u32], (x, y): Point<i8>, rgba: u32) {
    let index = y as usize * WIDTH + x as usize;
    debug_assert!(index < buffer.len());
    *buffer.get_unchecked_mut(index) = rgba;
}

fn main() {
    let mut buffer = [0_u32; WIDTH * HEIGHT];

    // The clipping region is closed/inclusive, thus 1 needs to be subtracted from the size.
    let clip = Clip::<i8>::new((0, 0), (WIDTH as i8 - 1, HEIGHT as i8 - 1)).unwrap();

    // `Clip` has convenience methods for the general iterators.
    clip.any_octant((-128, -100), (100, 80))
        // None if the line segment is completely invisible.
        // You might want to handle that case differently.
        .unwrap()
        // clipped to [(0, 1), ..., (58, 47)]
        .for_each(|xy| {
            // SAFETY: (x, y) has been clipped to the buffer.
            unsafe { draw(&mut buffer, xy, RGBA) }
        });

    // Alternatively, use the iterator constructors.
    AnyOctant::<i8>::clip((12, 0), (87, 23), &clip)
        .into_iter()
        .flatten()
        // clipped to [(12, 0), ..., (63, 16)]
        .for_each(|xy| {
            // SAFETY: (x, y) has been clipped to the buffer.
            unsafe { draw(&mut buffer, xy, RGBA) }
        });

    // Horizontal and vertical line segments.
    clip.axis_0(32, 76, -23)
        .unwrap()
        // clipped to [(63, 32), ..., (0, 32)]
        .for_each(|xy| {
            // SAFETY: (x, y) has been clipped to the buffer.
            unsafe { draw(&mut buffer, xy, RGBA) }
        });

    clip.axis_1(32, -23, 76)
        .unwrap()
        // clipped to [(32, 0), ..., (32, 47)]
        .for_each(|xy| {
            // SAFETY: (x, y) has been clipped to the buffer.
            unsafe { draw(&mut buffer, xy, RGBA) }
        });

    // Unclipped iterators are also available.
    // (-2, -2) -> (12, 12) is covered by Diagonal0, we can construct it directly.
    Diagonal0::<i8>::new((-2, -2), (12, 12))
        .unwrap()
        // Need to check every pixel to avoid going out of bounds.
        .filter(|&xy| clip.point(xy))
        .for_each(|xy| {
            // SAFETY: (x, y) is inside the buffer.
            unsafe { draw(&mut buffer, xy, RGBA) }
        });
}

Limitations

• To support usage in const contexts, types must have an inherent implementation for every supported numeric type instead of relying on a trait. This and Rust's lack of support for function overloading means that the numeric type parameter must always be specified.
• Currently, only half-open line segments can be iterated. This allows ExactSizeIterator to be implemented for all types. Inclusive iterators are tracked in #1.

Benchmarks

• divan is used to benchmark different versions of clipline, as well as line_drawing. Use cargo bench to run the benchmarks.
• In practice, with unclipped line segments, bounds checks are required when indexing into a grid, hence the difference between the draw_pixel_checked and draw_pixel_unchecked functions.

References

clipline is inspired by the following papers:

• A fast two-dimensional line clipping algorithm via line encoding, Mark S. Sobkow, Paul Pospisil, Yee-Hong Yang, 1987.
• A new approach to parametric line clipping, Michael Dörr, 1990.
• Bresenham's Line Generation Algorithm with Built-in Clipping, Yevgeny P. Kuzmin, 1995.