From 9f4a8f03dfedcefedee62381d2b6ddcf6a52f07e Mon Sep 17 00:00:00 2001
From: Joe Ardent <code@ardent.nebcorp.com>
Date: Mon, 8 Sep 2025 14:41:03 -0700
Subject: [PATCH] fix triangle interpolation

---
 src/main.rs  | 16 ++++++++++------
 src/point.rs | 45 +++++++++++++++++++++++++++++++++++++++++----
 src/tga.rs   | 17 ++++++++++++++++-
 3 files changed, 67 insertions(+), 11 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index eb21adb..538867d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -46,6 +46,10 @@ fn main() {
     let b = Point2i::new(550, 390).with_color(GREEN);
     let c = Point2i::new(230, 590).with_color(RED);
 
+    a.render(20, &mut fb);
+    b.render(20, &mut fb);
+    c.render(20, &mut fb);
+
     let t = Triangle2i::new(a, b, c);
     t.render_filled(BLACK, &mut fb);
     fb.write_file("triangle.tga", true, true).unwrap();
@@ -112,12 +116,12 @@ impl Triangle2i {
             return;
         }
         let it = 1.0 / total_area;
-        (bb.ymin()..=bb.ymax()).into_par_iter().for_each(|y| {
-            (bb.xmin()..bb.xmax()).into_par_iter().for_each(|x| {
+        (bb.xmin()..=bb.xmax()).into_par_iter().for_each(|x| {
+            (bb.ymin()..=bb.ymax()).into_par_iter().for_each(|y| {
                 let p = Point2i::new(x, y);
-                let alpha = Triangle2i::new(p, self.a, self.b).signed_area() * it;
-                let beta = Triangle2i::new(p, self.b, self.c).signed_area() * it;
-                let gamma = Triangle2i::new(p, self.c, self.a).signed_area() * it;
+                let alpha = Triangle2i::new(p, self.b, self.c).signed_area() * it;
+                let beta = Triangle2i::new(p, self.c, self.a).signed_area() * it;
+                let gamma = Triangle2i::new(p, self.a, self.b).signed_area() * it;
 
                 if alpha.is_sign_positive()
                     && beta.is_sign_positive()
@@ -128,7 +132,7 @@ impl Triangle2i {
                         && let Some(cb) = self.b.color
                         && let Some(cc) = self.c.color
                     {
-                        ca * alpha + cb * beta + cc * gamma + color
+                        color + (ca * alpha) + (cb * beta) + (cc * gamma)
                     } else {
                         color
                     };
diff --git a/src/point.rs b/src/point.rs
index 122ae14..35c785e 100644
--- a/src/point.rs
+++ b/src/point.rs
@@ -1,6 +1,14 @@
-use std::ops::{Add, Deref, DerefMut, Div, Mul, Sub};
+use std::{
+    ops::{Add, Deref, DerefMut, Div, Mul, Sub},
+    sync::{Arc, Mutex},
+};
 
-use crate::tga::TGAColor;
+use rayon::iter::{IntoParallelIterator, ParallelIterator};
+
+use crate::{
+    YELLOW,
+    tga::{TGAColor, TGAImage},
+};
 
 #[derive(Default, Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Point2i {
@@ -28,6 +36,25 @@ impl Point2i {
             ..self
         }
     }
+
+    pub fn render(&self, radius: i32, fb: &mut TGAImage) {
+        let xmin = self.x - radius;
+        let xmax = self.x + radius;
+        let ymin = self.y - radius;
+        let ymax = self.y + radius;
+        let r2 = radius.pow(2);
+        let fb = Arc::new(Mutex::new(fb));
+        (ymin..=ymax).into_par_iter().for_each(|y| {
+            (xmin..=xmax).into_par_iter().for_each(|x| {
+                let d2 = (x - self.x).pow(2) + (y - self.y).pow(2);
+                if d2 <= r2
+                    && let Ok(mut fb) = fb.lock()
+                {
+                    fb.set(x as u32, y as u32, self.color.unwrap_or(YELLOW));
+                }
+            });
+        });
+    }
 }
 
 impl Add for Point2i {
@@ -37,7 +64,12 @@ impl Add for Point2i {
         Self {
             x: self.x + rhs.x,
             y: self.y + rhs.y,
-            color: None,
+            color: if self.color.is_none() {
+                rhs.color
+            } else {
+                self.color
+                    .map(|c| if let Some(oc) = rhs.color { c + oc } else { c })
+            },
         }
     }
 }
@@ -49,7 +81,12 @@ impl Sub for Point2i {
         Self {
             x: self.x - rhs.x,
             y: self.y - rhs.y,
-            color: None,
+            color: if self.color.is_none() {
+                rhs.color
+            } else {
+                self.color
+                    .map(|c| if let Some(oc) = rhs.color { c - oc } else { c })
+            },
         }
     }
 }
diff --git a/src/tga.rs b/src/tga.rs
index f8e5409..2a28a7e 100644
--- a/src/tga.rs
+++ b/src/tga.rs
@@ -1,7 +1,7 @@
 use std::{
     fs::File,
     io::{Read, Write},
-    ops::{Add, Deref, DerefMut, Mul},
+    ops::{Add, Deref, DerefMut, Mul, Sub},
 };
 
 const HEADER_SIZE: usize = 18;
@@ -88,6 +88,21 @@ impl Add for TGAColor {
     }
 }
 
+impl Sub for TGAColor {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        Self {
+            bgra: [
+                self[0].saturating_sub(rhs[0]),
+                self[1].saturating_sub(rhs[1]),
+                self[2].saturating_sub(rhs[2]),
+                self[3].saturating_sub(rhs[3]),
+            ],
+        }
+    }
+}
+
 impl Mul<f32> for TGAColor {
     type Output = Self;