From 1dab1af17aafa7c7843f11f46575cf6658f4796b Mon Sep 17 00:00:00 2001
From: bendn <bend.n@outlook.com>
Date: Mon, 11 Sep 2023 06:40:28 +0700
Subject: [PATCH] triangle drawing

---
 src/drawing/mod.rs |  3 ++-
 src/drawing/tri.rs | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 1 deletion(-)
 create mode 100644 src/drawing/tri.rs

diff --git a/src/drawing/mod.rs b/src/drawing/mod.rs
index 18bbc5d..8437083 100644
--- a/src/drawing/mod.rs
+++ b/src/drawing/mod.rs
@@ -1,2 +1,3 @@
-//! contains drawing operations, like line drawing
+//! contains drawing operations, like line drawing and triangle drawing
 mod line;
+mod tri;
diff --git a/src/drawing/tri.rs b/src/drawing/tri.rs
new file mode 100644
index 0000000..3cc390b
--- /dev/null
+++ b/src/drawing/tri.rs
@@ -0,0 +1,45 @@
+//! trongle drawing
+use crate::Image;
+
+impl<const CHANNELS: usize> Image<&mut [u8], CHANNELS> {
+    /// Draw a (filled) triangle
+    ///
+    /// # Safety
+    ///
+    /// UB if any point is out of bounds
+    /// ```
+    /// # use fimg::*;
+    /// let mut a = Image::alloc(10, 10);
+    /// // draw a triangle from point a v   point b v    point c v
+    /// //                                               with color white
+    /// unsafe { a.as_mut().tri((3.0, 2.0), (8.0, 7.0), (1.0, 8.0), [255]) };
+    /// # assert_eq!(a.buffer(), b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff\xff\x00\x00\x00\x00\x00\x00\x00\xff\xff\xff\xff\x00\x00\x00\x00\x00\xff\xff\xff\xff\xff\xff\x00\x00\x00\x00\xff\xff\xff\xff\xff\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00");
+    /// ```
+    pub unsafe fn tri(
+        &mut self,
+        (x1, y1): (f32, f32),
+        (x2, y2): (f32, f32),
+        (x3, y3): (f32, f32),
+        c: [u8; CHANNELS],
+    ) {
+        // TODO optimize
+        for y in y1.min(y2).min(y3) as u32..y1.max(y2).max(y3) as u32 {
+            for x in x1.min(x2).min(x3) as u32..x1.max(x2).max(x3) as u32 {
+                let s = (x1 - x3) * (y as f32 - y3) - (y1 - y2) * (x as f32 - x3);
+                let t = (x2 - x1) * (y as f32 - y1) - (y2 - y1) * (x as f32 - x1);
+
+                if (s < 0.0) != (t < 0.0) && s != 0.0 && t != 0.0 {
+                    continue;
+                }
+
+                let d = (x3 - x2) * (y as f32 - y2) - (y3 - y2) * (x as f32 - x2);
+                if d == 0.0 || (d < 0.0) == (s + t <= 0.0) {
+                    // SAFETY:
+                    // caller gurantees triangle is in bounds, this loops over the
+                    // bounding box of the triangle, therefore this is fine.
+                    unsafe { self.set_pixel(x, y, c) };
+                }
+            }
+        }
+    }
+}