From 10882983fef8733bbe6a6fea2fcc46aa627d8266 Mon Sep 17 00:00:00 2001
From: Joe Ardent <code@ardent.nebcorp.com>
Date: Sun, 7 Sep 2025 15:22:53 -0700
Subject: [PATCH] primitive back-culling

---
 src/main.rs | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 455fc32..3208373 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -39,13 +39,11 @@ fn main() {
     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();
 
     _render_head(&mut fb);
 }
 
-fn fill_triangles(fb: &mut TGAImage) {
+fn _fill_triangles(fb: &mut TGAImage) {
     let t1a = Point2i::new(7, 45);
     let t1b = Point2i::new(35, 100);
     let t1c = Point2i::new(45, 60);
@@ -175,17 +173,25 @@ 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_sign = self.signed_area().signum();
+        let total_area = self.signed_area();
+        if total_area < 1.0 {
+            return;
+        }
         (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().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;
+                let a = Triangle::new(p, self.a, self.b)
+                    .signed_area()
+                    .is_sign_positive();
+                let b = Triangle::new(p, self.b, self.c)
+                    .signed_area()
+                    .is_sign_positive();
+                let c = Triangle::new(p, self.c, self.a)
+                    .signed_area()
+                    .is_sign_positive();
 
-                if a.is_sign_positive()
-                    && b.is_sign_positive()
-                    && c.is_sign_positive()
+                if a && b
+                    && c
                     && let Ok(mut fb) = fb.lock()
                 {
                     fb.set(x as u32, y as u32, color);