rustic_zen/image/

software.rs

// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

//! Image contains the full colour depth framebuffer, and provides functions to export it.

use crate::{geom::Point, ray::RayResult};

use std::mem::swap;

use super::{ExportImage, RenderImage};

/// Represents an image while ray rendering is happening
///
/// This struct uses floats to represent each pixel of the image so normalisation
/// can happen after rendering finishes.
///
/// Image is created and populated by the renderer. Only export functions are exposed.
pub struct Image {
    width: usize,
    height: usize,
    pixels: Vec<(f32, f32, f32)>,
    lightpower: f32,
}

impl Image {
    /// Create new image with the given width and hieght;
    pub fn new(width: usize, height: usize) -> Self {
        let len = width * height;
        let pixels: Vec<(f32, f32, f32)> = vec![(0.0, 0.0, 0.0); len];
        Image {
            width,
            height,
            pixels,
            lightpower: 0.0,
        }
    }

    #[inline(always)]
    fn plot(&self, colour: (f32, f32, f32), pixel: usize, intensity: f32) {
        if pixel >= self.pixels.len() {
            return;
        };

        unsafe {
            // This is using statistical safety. A tyical image has over 8 million data points in it,
            // while even a high end CPU will likely only have 64 threads. Safety while not guarenteed
            // is provided "good enough" by the diminishinly small change of a read before write error
            // occuring in this large dataset, and the miniscule values the pixels are updated with by
            // each ray.
            //
            // NB: This is not actually safe. Small data errors will occur. We however don't consider
            // them significant.
            let s = (self as *const Self) as *mut Self;
            (*s).pixels[pixel].0 += colour.0 * intensity;
            (*s).pixels[pixel].1 += colour.1 * intensity;
            (*s).pixels[pixel].2 += colour.2 * intensity;
        }
    }

    #[inline(always)]
    fn inner_draw_line(&self, ray: &RayResult) {
        /*
         * Modified version of Xiaolin Wu's antialiased line algorithm:
         * http://en.wikipedia.org/wiki/Xiaolin_Wu%27s_line_algorithm
         *
         * Brightness compensation:
         *   The total brightness of the line should be proportional to its
         *   length, but with Wu's algorithm it's proportional to dx.
         *   We scale the brightness of each pixel to compensate.
         */

        let bounds =
            Self::check_bounds(ray.origin, ray.termination, self.width - 1, self.height + 2);
        if bounds.is_none() {
            return;
        }

        let colour = ray.color();

        let (p0, p1) = bounds.unwrap();

        let mut hx: i64 = 1;
        let mut hy: i64 = self.width as i64;

        let mut x0 = p0.x;
        let mut y0 = p0.y;
        let mut x1 = p1.x;
        let mut y1 = p1.y;

        let dx = (x1 - x0).abs();
        let dy = (y1 - y0).abs();

        // Axis swap. The virtual 'x' is always the major axis.
        if dy > dx {
            swap(&mut x0, &mut y0);
            swap(&mut x1, &mut y1);
            swap(&mut hx, &mut hy);
        }

        // We expect x0->x1 to be in the +X direction
        if x0 > x1 {
            swap(&mut x0, &mut x1);
            swap(&mut y0, &mut y1);
        }

        // calculate gradient
        let dx = x1 - x0;
        let dy = y1 - y0;
        let gradient = if dx == 0.0 { 1.0 } else { dy / dx };

        const SHIFT: f64 = 0.25;

        x0 -= SHIFT;
        x1 += SHIFT;
        y0 -= gradient * SHIFT;
        y1 += gradient * SHIFT;

        // Brightness Calculation
        let br = 128.0 * f64::sqrt(dx * dx + dy * dy) / dx;

        // TODO clipping here

        // Handle first endpoint
        let xend = x0.round();
        let yend = y0 + gradient * (xend - x0);
        let xpxl1: i64 = xend as i64;
        let ypxl1: i64 = yend.floor() as i64;

        let xgap = br * (1.0 - (x0 + 0.5) + xend); // 0 to br
        let ygap = yend - yend.floor(); // 0 to 1

        self.plot(
            colour,
            (xpxl1 * hx + ypxl1 * hy) as usize,
            (xgap * (1.0 - ygap)) as f32,
        );
        self.plot(
            colour,
            (xpxl1 * hx + (ypxl1 + 1) * hy) as usize,
            (xgap * ygap) as f32,
        );

        let mut intery = yend + gradient;

        //Handle Second endpoint
        let xend = x1.round();
        let yend = y1 + gradient * (xend - x1);
        let xpxl2: i64 = xend as i64;
        let ypxl2: i64 = yend.floor() as i64;

        let xgap = br * (1.0 - (x1 + 0.5) + xend); // 0 to br
        let ygap = yend - yend.floor(); // 0 to 1

        self.plot(
            colour,
            (xpxl2 * hx + ypxl2 * hy) as usize,
            (xgap * (1.0 - ygap)) as f32,
        );
        self.plot(
            colour,
            (xpxl2 * hx + (ypxl2 + 1) * hy) as usize,
            (xgap * ygap) as f32,
        );

        // Loop Over line
        for x in xpxl1 + 1..xpxl2 {
            let iy: i64 = intery.floor() as i64;
            let fy: f64 = intery - intery.floor(); // 0 to 1

            self.plot(
                colour,
                (x * hx + iy * hy) as usize,
                (br * (1.0 - fy)) as f32,
            );
            self.plot(colour, (x * hx + (iy + 1) * hy) as usize, (br * fy) as f32);

            intery += gradient;
        }
    }

    #[inline(always)]
    fn check_bounds(
        mut p0: Point,
        mut p1: Point,
        width: usize,
        height: usize,
    ) -> Option<(Point, Point)> {
        let width = (width) as f64;
        let height = (height) as f64;

        if (p0.x < 0.0 && p1.x < 0.0) ||  // if both are less than 0 the line is not in frame
           (p0.y < 0.0 && p1.y < 0.0) || // if both are less than 0 the line is not in frame
           (p0.x > width && p1.x > width) || // if both are greater than width the line is not in frame
           (p0.y > height && p1.y > height)
        // if both are greater than height the line is not in frame
        {
            return None;
        }

        if p0.x > p1.x {
            swap(&mut p0, &mut p1);
        }

        let d = (p1 - p0).normalized();

        if d.x == 0.0 {
            p0.y = p0.y.clamp(0.0, height);
            p1.y = p1.y.clamp(0.0, height);
        } else {
            if p0.x < 0.0 {
                p0 = p0 - (d * (p0.x / d.x));
            }
            if p1.x > width {
                p1 = p1 - d * ((p1.x - width) / d.x);
            }
            if p0.y < 0.0 {
                p0 = p0 - (d * (p0.y / d.y));
            } else {
                if p0.y > height {
                    p0 = p0 - d * ((p0.y - height) / d.y);
                }
            }
            if p1.y < 0.0 {
                p1 = p1 - (d * (p1.y / d.y));
            } else {
                if p1.y > height {
                    p1 = p1 - d * ((p1.y - height) / d.y);
                }
            }
        }
        Some((p0, p1))
    }
}

impl RenderImage for Image {
    fn draw_line(&self, ray: RayResult) {
        self.inner_draw_line(&ray);
    }

    fn prepare_render(&mut self, lightpower: f32) {
        self.lightpower = lightpower;
    }
}

impl ExportImage for Image {
    fn get_lightpower(&self) -> f32 {
        self.lightpower
    }

    fn get_size(&self) -> (usize, usize) {
        (self.width, self.height)
    }

    fn to_rgbaf32(&self) -> Vec<f32> {
        self.pixels
            .clone()
            .into_iter()
            .map(|x| [x.0, x.1, x.2, 1.0f32])
            .flatten()
            .collect()
    }
}

#[cfg(test)]
mod tests {
    use super::Image;
    use crate::image::{ExportImage, RenderImage};
    use crate::prelude::Point;
    use crate::ray::RayResult;

    #[test]
    fn traced_ray_is_not_black() {
        let i = Image::new(100, 100);
        i.draw_line(RayResult::new((10.0, 10.0), (90.0, 90.0), 620.0)); //red
        i.draw_line(RayResult::new((20.0, 10.0), (90.0, 80.0), 520.0)); //green
        i.draw_line(RayResult::new((10.0, 20.0), (80.0, 90.0), 470.0)); //blue
        let mut r_count = 0.0;
        let mut g_count = 0.0;
        let mut b_count = 0.0;
        for (r, g, b) in i.pixels.iter() {
            r_count += r;
            g_count += g;
            b_count += b;
        }
        assert_ne!(r_count, 0.0);
        assert_ne!(g_count, 0.0);
        assert_ne!(b_count, 0.0);
    }

    #[test]
    fn empty_image_is_black() {
        let mut i = Image::new(1920, 1080);
        i.prepare_render(1.0);
        let v = i.to_rgba8(0, 1.0, 1.0);
        for i in v.chunks(4) {
            assert_eq!(i[0], 0u8);
            assert_eq!(i[1], 0u8);
            assert_eq!(i[2], 0u8);
            assert_eq!(i[3], 255u8);
        }
    }

    #[test]
    fn output_len_u8() {
        let i = Image::new(1920, 1080);
        let v = i.to_rgba8(0, 1.0, 1.0);
        assert_eq!(v.len(), 1920 * 1080 * 4);
    }

    #[test]
    fn output_len_f32() {
        let i = Image::new(1920, 1080);
        let v = i.to_rgbaf32();
        assert_eq!(v.len(), 1920 * 1080 * 4);
    }

    #[test]
    fn contigious_lines() {
        let i = Image::new(400, 400);
        i.draw_line(RayResult::new((10.0, 10.0), (100.0, 100.0), 0.0));
        i.draw_line(RayResult::new((100.0, 100.0), (200.0, 200.0), 0.0));
        i.draw_line(RayResult::new((200.0, 200.0), (300.0, 300.0), 0.0));
        i.draw_line(RayResult::new((300.0, 300.0), (390.0, 390.0), 0.0));

        for x in 0..10 {
            for y in 0..400 {
                let p = i.pixels[(y * 400) + x];
                assert_eq!(p.0, 0.0);
                assert_eq!(p.1, 0.0);
                assert_eq!(p.2, 0.0);
            }
        }

        for x in 10..=390 {
            for y in 0..400 {
                let p = i.pixels[(y * 400) + x];
                if x == y {
                    assert!(p.0 > 0.0);
                    assert!(p.1 > 0.0);
                    assert!(p.2 > 0.0);
                } else {
                    assert_eq!(p.0, 0.0);
                    assert_eq!(p.1, 0.0);
                    assert_eq!(p.2, 0.0);
                }
            }
        }

        for x in 391..400 {
            for y in 0..400 {
                let p = i.pixels[(y * 400) + x];
                assert_eq!(p.0, 0.0);
                assert_eq!(p.1, 0.0);
                assert_eq!(p.2, 0.0);
            }
        }
    }

    #[test]
    fn line_correct() {
        let i = Image::new(100, 100);
        i.draw_line(RayResult::new((0.0, 0.0), (100.0, 100.0), 0.0)); //green
        for x in 0..100 {
            for y in 0..100 {
                let p = i.pixels[(y * 100) + x];
                if x == y {
                    assert!(p.0 > 0.0);
                    assert!(p.1 > 0.0);
                    assert!(p.2 > 0.0);
                } else {
                    assert_eq!(p.0, 0.0);
                    assert_eq!(p.1, 0.0);
                    assert_eq!(p.2, 0.0);
                }
            }
        }
    }

    #[test]
    fn bounds_check_left1() {
        let p0 = Point::new(-10.0, 0.0);
        let p1 = Point::new(10.0, 20.0);

        let (p0, p1) = Image::check_bounds(p0, p1, 50, 50).unwrap();

        assert_eq!(p0, (0.0, 10.0).into());
        assert_eq!(p1, (10.0, 20.0).into());
    }

    #[test]
    fn bounds_check_left2() {
        let p1 = Point::new(-10.0, 0.0);
        let p0 = Point::new(10.0, 20.0);

        let (p0, p1) = Image::check_bounds(p0, p1, 50, 50).unwrap();

        assert_eq!(p0, (0.0, 10.0).into());
        assert_eq!(p1, (10.0, 20.0).into());
    }

    #[test]
    fn bounds_check_right1() {
        let p0 = Point::new(60.0, 0.0);
        let p1 = Point::new(40.0, 20.0);

        let (p0, p1) = Image::check_bounds(p0, p1, 50, 50).unwrap();

        assert_eq!(p1, (50.0, 10.0).into());
        assert_eq!(p0, (40.0, 20.0).into());
    }

    #[test]
    fn bounds_check_right2() {
        let p1 = Point::new(60.0, 0.0);
        let p0 = Point::new(40.0, 20.0);

        let (p0, p1) = Image::check_bounds(p0, p1, 50, 50).unwrap();

        assert_eq!(p1, (50.0, 10.0).into());
        assert_eq!(p0, (40.0, 20.0).into());
    }

    #[test]
    fn bounds_check_top1() {
        let p0 = Point::new(20.0, -10.0);
        let p1 = Point::new(40.0, 10.0);

        let (p0, p1) = Image::check_bounds(p0, p1, 50, 50).unwrap();

        assert_eq!(p0, (30.0, 0.0).into());
        assert_eq!(p1, (40.0, 10.0).into());
    }

    #[test]
    fn bounds_check_top2() {
        let p1 = Point::new(20.0, -10.0);
        let p0 = Point::new(40.0, 10.0);

        let (p0, p1) = Image::check_bounds(p0, p1, 50, 50).unwrap();

        assert_eq!(p0, (30.0, 0.0).into());
        assert_eq!(p1, (40.0, 10.0).into());
    }

    #[test]
    fn bounds_check_bottom1() {
        let p0 = Point::new(10.0, 60.0);
        let p1 = Point::new(40.0, 30.0);

        let (p0, p1) = Image::check_bounds(p0, p1, 50, 50).unwrap();

        assert_eq!(p0, (20.0, 50.0).into());
        assert_eq!(p1, (40.0, 30.0).into());
    }

    #[test]
    fn bounds_check_bottom2() {
        let p1 = Point::new(10.0, 60.0);
        let p0 = Point::new(40.0, 30.0);

        let (p0, p1) = Image::check_bounds(p0, p1, 50, 50).unwrap();

        assert_eq!(p0, (20.0, 50.0).into());
        assert_eq!(p1, (40.0, 30.0).into());
    }
}