there's a missing scanline in the white triangle

src/main.rs

@@ -2,6 +2,8 @@
 extern crate justerror;
 
 mod tga;
+use std::collections::BTreeMap;
+
 use rand::Rng;
 use tga::*;
 
@@ -32,25 +34,39 @@ const YELLOW: TGAColor = TGAColor {
 };
 
 fn main() {
-    let w = 800;
-    let h = 800;
-    let mut framebuffer = TGAImage::new(w, h, TGAFormat::RGB);
-    let model = Model::from_obj("diablo3_pose.obj");
+    let w = 128;
+    let h = 128;
+    let mut fb = TGAImage::new(w, h, TGAFormat::RGB);
+    fill_triangles(&mut fb);
+    fb.write_file("triangles.tga", true, true).unwrap();
+}
 
-    dbg!(model.verts.len());
-    let mut max_face = 0usize;
-    let mut min_face = usize::MAX;
+fn fill_triangles(fb: &mut TGAImage) {
+    /*
+    triangle(  7, 45, 35, 100, 45,  60, framebuffer, red);
+    triangle(120, 35, 90,   5, 45, 110, framebuffer, white);
+    triangle(115, 83, 80,  90, 85, 120, framebuffer, green);
+    */
 
-    for f in model.faces.iter() {
-        for &f in f.iter() {
-            max_face = f.max(max_face);
-            min_face = f.min(min_face);
-        }
-    }
+    let t1a = Point2i::new(7, 45);
+    let t1b = Point2i::new(35, 100);
+    let t1c = Point2i::new(45, 60);
+    triangle_filled(t1a, t1b, t1c, RED, fb);
 
-    model.render_wireframe(&mut framebuffer);
+    let t2a = Point2i::new(120, 35);
+    let t2b = Point2i::new(90, 5);
+    let t2c = Point2i::new(45, 110);
+    triangle_filled(t2a, t2b, t2c, WHITE, fb);
 
-    framebuffer.write_file("diablo.tga", true, true).unwrap();
+    let a = Point2i::new(115, 83);
+    let b = Point2i::new(80, 90);
+    let c = Point2i::new(85, 120);
+    triangle_filled(a, b, c, GREEN, fb);
+}
+
+fn _render_diablo(model: Model, fb: &mut TGAImage) {
+    model.render_wireframe(fb);
+    fb.write_file("diablo.tga", true, true).unwrap();
 }
 
 fn _baseline(framebuffer: &mut TGAImage) {
@@ -69,10 +85,10 @@ fn _baseline(framebuffer: &mut TGAImage) {
     let b = Point2i::newu(bx, by);
     let c = Point2i::newu(cx, cy);
 
-    line(a, b, framebuffer, BLUE);
-    line(c, b, framebuffer, GREEN);
-    line(c, a, framebuffer, YELLOW);
-    line(a, c, framebuffer, RED);
+    line(a, b, BLUE, framebuffer);
+    line(c, b, GREEN, framebuffer);
+    line(c, a, YELLOW, framebuffer);
+    line(a, c, RED, framebuffer);
 }
 
 fn _bench(fb: &mut TGAImage) {
@@ -90,13 +106,20 @@ fn _bench(fb: &mut TGAImage) {
         line(
             a,
             b,
-            fb,
             [rng.random(), rng.random(), rng.random(), rng.random()].into(),
+            fb,
         );
     }
 }
 
-fn line(mut a: Point2i, mut b: Point2i, fb: &mut TGAImage, color: TGAColor) {
+fn line(a: Point2i, b: Point2i, color: TGAColor, fb: &mut TGAImage) {
+    let verts = line_verts(a, b);
+    for v in verts.into_iter() {
+        fb.set(v.x as u32, v.y as u32, color);
+    }
+}
+
+fn line_verts(mut a: Point2i, mut b: Point2i) -> Vec<Point2i> {
     let is_steep = (a.x - b.x).abs() < (a.y - b.y).abs();
     if is_steep {
         std::mem::swap(&mut a.x, &mut a.y);
@@ -107,14 +130,63 @@ fn line(mut a: Point2i, mut b: Point2i, fb: &mut TGAImage, color: TGAColor) {
         std::mem::swap(&mut a.y, &mut b.y);
     }
 
-    let mut y = a.y as f32;
+    let mut verts: Vec<Point2i> = Vec::new();
+
     let step = (b.y - a.y) as f32 / (b.x - a.x) as f32;
+    let sign = step.signum() as i32;
+    let mut y = a.y as f32;
     for x in (a.x)..b.x {
-        if is_steep {
-            fb.set(y as u32, x as u32, color);
+        let p = if is_steep {
+            Point2i::new(y.round_ties_even() as i32, x)
         } else {
-            fb.set(x as u32, y as u32, color);
-        }
+            Point2i::new(x, y.round_ties_even() as i32)
+        };
+        verts.push(p);
         y += step;
     }
+
+    verts
+}
+
+fn triangle_lines(a: Point2i, b: Point2i, c: Point2i, color: TGAColor, fb: &mut TGAImage) {
+    line(a, b, color, fb);
+    line(b, c, color, fb);
+    line(c, a, color, fb);
+}
+
+fn triangle_filled(a: Point2i, b: Point2i, c: Point2i, color: TGAColor, fb: &mut TGAImage) {
+    let mut verts = line_verts(a, b);
+    verts.extend(line_verts(b, c));
+    verts.extend(line_verts(c, a));
+
+    let mut lines: BTreeMap<i32, Vec<i32>> = BTreeMap::new();
+    for vert in verts.into_iter() {
+        lines
+            .entry(vert.y)
+            .and_modify(|e| {
+                e.push(vert.x);
+                e.sort_unstable();
+            })
+            .or_insert(vec![vert.x]);
+    }
+
+    let mut prev_y: Option<i32> = None;
+    for (y, xs) in lines.iter_mut() {
+        let len = xs.len();
+        match len {
+            0 => {}
+            1 => fb.set(xs[0] as u32, *y as u32, color),
+            _ => {
+                let start = xs[0];
+                let end = xs[len - 1];
+                line(Point2i::new(start, *y), Point2i::new(end, *y), color, fb);
+            }
+        }
+        if let Some(prev) = prev_y {
+            if (y - prev).abs() > 1 {
+                dbg!(y);
+            }
+        }
+        prev_y = Some(*y)
+    }
 }

src/model.rs

@@ -87,9 +87,9 @@ impl Model {
             let a = world2view(self.verts[face[0]], width, height);
             let b = world2view(self.verts[face[1]], width, height);
             let c = world2view(self.verts[face[2]], width, height);
-            line(a, b, framebuffer, RED);
-            line(b, c, framebuffer, RED);
-            line(c, a, framebuffer, RED);
+            line(a, b, RED, framebuffer);
+            line(b, c, RED, framebuffer);
+            line(c, a, RED, framebuffer);
         }
     }
 }

src/point.rs

@@ -10,6 +10,7 @@ impl Point2i {
     pub fn new(x: i32, y: i32) -> Self {
         Self { x, y }
     }
+
     pub fn newu(x: u32, y: u32) -> Self {
         Self {
             x: x as i32,