From 90420bdc72ce1ad8ba3611652b788ff7bc568f63 Mon Sep 17 00:00:00 2001
From: Joe Ardent <code@ardent.nebcorp.com>
Date: Sun, 7 Sep 2025 14:53:02 -0700
Subject: [PATCH] render head with random color triangles and no backface
 culling

---
 src/main.rs  | 62 ++++++++++++++++++++--------------------------------
 src/model.rs | 24 +++++++++++++++++++-
 2 files changed, 47 insertions(+), 39 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index d97f7c4..455fc32 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -36,11 +36,13 @@ const YELLOW: TGAColor = TGAColor {
 };
 
 fn main() {
-    let w = 128;
-    let h = 128;
+    let w = 800;
+    let h = 800;
     let mut fb = TGAImage::new(w, h, TGAFormat::RGB);
-    fill_triangles(&mut fb);
-    fb.write_file("triangles.tga", true, true).unwrap();
+    // fill_triangles(&mut fb);
+    // fb.write_file("triangles.tga", true, true).unwrap();
+
+    _render_head(&mut fb);
 }
 
 fn fill_triangles(fb: &mut TGAImage) {
@@ -63,11 +65,17 @@ fn fill_triangles(fb: &mut TGAImage) {
     t3.render_filled(GREEN, fb);
 }
 
-fn _render_diablo(model: Model, fb: &mut TGAImage) {
+fn _render_diablo(fb: &mut TGAImage) {
+    let model = Model::from_obj("diablo3_pose.obj");
     model.render_wireframe(fb);
     fb.write_file("diablo.tga", true, true).unwrap();
 }
 
+fn _render_head(fb: &mut TGAImage) {
+    let model = Model::from_obj("head.obj");
+    model.render_triangles(fb);
+    fb.write_file("head.tga", true, true).unwrap();
+}
 fn _baseline(framebuffer: &mut TGAImage) {
     let ax = 7;
     let ay = 3;
@@ -121,30 +129,17 @@ fn line(mut a: Point2i, mut b: Point2i, color: TGAColor, mut fb: &mut TGAImage)
         std::mem::swap(&mut a, &mut b);
     }
 
-    let fb = Arc::new(Mutex::new(fb));
-    let y = Arc::new(Mutex::new(a.y as f32));
-
     let step = (b.y - a.y) as f32 / (b.x - a.x) as f32;
-    (a.x..b.x).into_par_iter().for_each(|x| {
-        let ny = {
-            if let Ok(y) = y.lock() {
-                *y
-            } else {
-                return;
-            }
-        };
+    let mut y = a.y as f32;
+    for x in a.x..b.x {
         let (px, py) = if is_steep {
-            (ny.round_ties_even() as i32, x)
+            (y.round_ties_even() as i32, x)
         } else {
-            (x, ny.round_ties_even() as i32)
+            (x, y.round_ties_even() as i32)
         };
-        if let Ok(mut fb) = fb.lock() {
-            fb.set(px as u32, py as u32, color);
-        }
-        if let Ok(mut y) = y.lock() {
-            *y += step;
-        }
-    });
+        fb.set(px as u32, py as u32, color);
+        y += step;
+    }
 }
 
 #[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
@@ -159,15 +154,6 @@ impl Triangle {
         Self { a, b, c }
     }
 
-    pub fn sort(&mut self) {
-        let mut sorted = [self.a, self.b, self.c];
-        sorted.sort_unstable_by(|a, b| a.y.cmp(&b.y));
-        let [a, b, c] = sorted;
-        self.a = a;
-        self.b = b;
-        self.c = c;
-    }
-
     pub fn signed_area(&self) -> f32 {
         0.5 * ((self.b.y - self.a.y) * (self.a.x + self.b.x)
             + (self.c.y - self.b.y) * (self.c.x + self.b.x)
@@ -189,13 +175,13 @@ impl Triangle {
     pub fn render_filled(&self, color: TGAColor, fb: &mut TGAImage) {
         let fb = Arc::new(Mutex::new(fb));
         let bb = self.bb();
-        let total_area = self.signed_area();
+        let total_area_sign = self.signed_area().signum();
         (bb.ymin()..=bb.ymax()).into_par_iter().for_each(|y| {
             (bb.xmin()..bb.xmax()).into_par_iter().for_each(|x| {
                 let p = Point2i::new(x, y);
-                let a = Triangle::new(p, self.a, self.b).signed_area() / total_area;
-                let b = Triangle::new(p, self.b, self.c).signed_area() / total_area;
-                let c = Triangle::new(p, self.c, self.a).signed_area() / total_area;
+                let a = Triangle::new(p, self.a, self.b).signed_area().signum() * total_area_sign;
+                let b = Triangle::new(p, self.b, self.c).signed_area().signum() * total_area_sign;
+                let c = Triangle::new(p, self.c, self.a).signed_area().signum() * total_area_sign;
 
                 if a.is_sign_positive()
                     && b.is_sign_positive()
diff --git a/src/model.rs b/src/model.rs
index 2bb51ae..2ba6070 100644
--- a/src/model.rs
+++ b/src/model.rs
@@ -1,7 +1,9 @@
 use std::ops::{Deref, DerefMut};
 
+use rand::Rng;
+
 use crate::{
-    RED, line,
+    RED, Triangle, line,
     point::{Point2i, Point3f},
     tga::TGAImage,
 };
@@ -92,6 +94,26 @@ impl Model {
             line(c, a, RED, framebuffer);
         }
     }
+    pub fn render_triangles(&self, framebuffer: &mut TGAImage) {
+        let width = framebuffer.width;
+        let height = framebuffer.height;
+
+        let mut rng = rand::rng();
+        for face in self.faces.iter() {
+            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);
+            let triangle = Triangle::new(a, b, c);
+            let color = [
+                rng.random_range(0..=255u8),
+                rng.random_range(0..=255u8),
+                rng.random_range(0..=255u8),
+                255,
+            ]
+            .into();
+            triangle.render_filled(color, framebuffer);
+        }
+    }
 }
 
 fn world2view(point: Point3f, width: u32, height: u32) -> Point2i {