From ed1bc978288249bdb1204d67c22c5186b78aea98 Mon Sep 17 00:00:00 2001
From: Altagos <altagos@posteo.de>
Date: Thu, 29 Feb 2024 15:21:22 +0100
Subject: [PATCH] added a sphere

---
 src/ray.zig | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/ray.zig b/src/ray.zig
index 0e41229..5e8a6dd 100644
--- a/src/ray.zig
+++ b/src/ray.zig
@@ -13,7 +13,20 @@ pub fn init(origin: zm.Vec, direction: zm.Vec) Ray {
 }
 
 pub fn color(self: *Ray) zm.Vec {
+    if (hit_sphere(zm.f32x4(0, 0, -1, 0), 0.5, self)) {
+        return zm.f32x4(1, 0, 0, 1);
+    }
+
     const unit_direction = zm.normalize3(self.dir);
     const a = 0.5 * (unit_direction[1] + 1.0);
     return zm.f32x4s(1.0 - a) * zm.f32x4s(1.0) + zm.f32x4s(a) * zm.f32x4(0.5, 0.7, 1.0, 1.0);
 }
+
+fn hit_sphere(center: zm.Vec, radius: f32, r: *Ray) bool {
+    const oc = r.orig - center;
+    const a = zm.dot3(r.dir, r.dir)[0];
+    const b = 2.0 * zm.dot3(oc, r.dir)[0];
+    const c = zm.dot3(oc, oc)[0] - radius * radius;
+    const discriminant = b * b - 4 * a * c;
+    return discriminant >= 0;
+}
-- 
2.51.2