From d1f29580aeb6d4e0d2e6f54bef61a9ad46a69926 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cobrien@witekio.com>
Date: Sat, 27 Sep 2025 14:07:41 +0100
Subject: [PATCH] Implement perspective projection matrix computation

---
 main.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/main.c b/main.c
index 5eb3813..b97b41c 100644
--- a/main.c
+++ b/main.c
@@ -9,6 +9,9 @@
 #define M_PI 3.14159265358979324
 #endif
 
+#define W 800
+#define H 600
+
 static const vertex_t vertices[] = {
 	{ { -1, -1 }, { 1, 0, 0 } },
 	{ { 1, -1 }, { 0, 1, 0 } },
@@ -78,13 +81,30 @@ static void mul(mat4_t out, const mat4_t left, const mat4_t right)
 	}
 }
 
+static void persp(mat4_t out, float aspect, float fov, float ncp, float fcp)
+{
+	const float r = 2 * ncp * tanf(fov / 2);
+	const float t = r * aspect;
+
+	// clang-format off
+	const mat4_t m = {
+		ncp / t, 0,        0,                        0,
+		0,       -ncp / r, 0,                        0,
+		0,       0,        fcp / (fcp - ncp),        1,
+		0,       0,        -fcp * ncp / (fcp - ncp), 0,
+	};
+	// clang-format on
+
+	memcpy(out, m, sizeof(mat4_t));
+}
+
 int main()
 {
 	// Set up window
 	glfwInit();
 	glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
 	glfwWindowHint(GLFW_RESIZABLE, GLFW_FALSE);
-	GLFWwindow *window = glfwCreateWindow(800, 800, "Foo", nullptr, nullptr);
+	GLFWwindow *window = glfwCreateWindow(W, H, "Foo", nullptr, nullptr);
 	assert(window);
 
 	// Register input callbacks
@@ -103,10 +123,10 @@ int main()
 	gpu_init(&gpu, &gpu_config);
 
 	mvp_t mvp = {
-		.model = SCALE(0.2),
-		.view = TRANSLATE(0, 0, 0.5),
-		.proj = ID,
+		.model = ID,
+		.view = TRANSLATE(0, 0, 4.0),
 	};
+	persp(mvp.proj, (float)W / H, M_PI / 6, 0.1, 10.0);
 
 	const mat4_t rot = ROT_Y(M_PI / 128);
 	while (!glfwWindowShouldClose(window)) {