From a73975a7668afcb838883febf6c2f44323240aab Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cobrien@witekio.com>
Date: Sat, 4 Oct 2025 20:44:24 +0100
Subject: [PATCH] Create orthographic projection function

---
 linear_alg.c | 10 ++++++++++
 linear_alg.h |  1 +
 main.c       |  4 +++-
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/linear_alg.c b/linear_alg.c
index 610f74b..a79e3bf 100644
--- a/linear_alg.c
+++ b/linear_alg.c
@@ -100,6 +100,16 @@ mat4_t mat4_perspective(float aspect, float fov, float near, float far)
 	};
 }
 
+mat4_t mat4_orthographic(float width, float height, float near, float far)
+{
+	return (mat4_t) {
+		{ 1 / width, 0, 0, 0 },
+		{ 0, -1 / height, 0, 0 },
+		{ 0, 0, 1 / (far - near), 0 },
+		{ 0, 0, -near / (far - near), 1 },
+	};
+}
+
 mat4_t mat4_translate_vec3(vec3_t v)
 {
 	return (mat4_t) {
diff --git a/linear_alg.h b/linear_alg.h
index 6bcf192..539d443 100644
--- a/linear_alg.h
+++ b/linear_alg.h
@@ -86,6 +86,7 @@ float vec4_dot(vec4_t v, vec4_t u);
 mat4_t mat4_mul(mat4_t m, mat4_t n);
 mat4_t mat4_lookat(vec3_t camera, vec3_t target, vec3_t up);
 mat4_t mat4_perspective(float aspect, float fov, float near, float far);
+mat4_t mat4_orthographic(float width, float height, float near, float far);
 mat4_t mat4_translate_vec3(vec3_t v);
 mat4_t mat4_scale_vec3(vec3_t v);
 mat4_t mat4_rotate_quaternion(vec4_t q);
diff --git a/main.c b/main.c
index 09b769c..03891bc 100644
--- a/main.c
+++ b/main.c
@@ -64,7 +64,9 @@ int main(int argc, char *argv[])
 	const mat4_t view = mat4_lookat(cam, tgt, up);
 	const mat4_t proj = mat4_perspective((float)W / H, PI / 8, 0.1, 100.0);
 	const mat4_t vp = mat4_mul(proj, view);
-	const mat4_t light_vp = mat4_lookat(light, tgt, up);
+	const mat4_t light_view = mat4_lookat(light, tgt, up);
+	const mat4_t light_proj = mat4_orthographic(5, 5, 10);
+	const mat4_t light_vp = mat4_mul(light_proj, light_view);
 	mat4_t transforms[NELEMS(gpu_models)] = {
 		mat4_mul(
 		    MAT4_TRANSLATE(1, 0, 0),