From e0f3c7d2ff0ea0c1c5cf77c83dd1d462f9090b1a Mon Sep 17 00:00:00 2001
From: Luca Conte <main@lugico.de>
Date: Wed, 2 Apr 2025 17:26:16 +0200
Subject: [PATCH]  matrix math beginnings

---
 meson.build       |  3 ++-
 src/main.c        | 11 ++++++++
 src/matrix-math.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++
 src/matrix-math.h | 23 ++++++++++++++++
 4 files changed, 103 insertions(+), 1 deletion(-)
 create mode 100644 src/matrix-math.c
 create mode 100644 src/matrix-math.h

diff --git a/meson.build b/meson.build
index f4c14b5..89c9769 100644
--- a/meson.build
+++ b/meson.build
@@ -6,7 +6,8 @@ m_dep = cc.find_library('m', required : false)
 src_files = [
 	'./src/main.c',
 	'./src/shader.c',
-	'./src/log.c'
+	'./src/log.c',
+	'./src/matrix-math.c'
 ]
 
 executable('cg1',
diff --git a/src/main.c b/src/main.c
index f20b9e9..29b47e6 100644
--- a/src/main.c
+++ b/src/main.c
@@ -10,6 +10,7 @@
 #include "shader.h"
 #include "log.h"
 #include "shader.h"
+#include "matrix-math.h"
 
 #define STATUS_INTERVAL 0.5
 
@@ -78,6 +79,16 @@ void updateStatusDisplay() {
 }
 
 void init(void) {
+
+	mat4 t = {
+		1, 2, 3, 4,
+		5, 6, 7, 8,
+		9, 10, 11, 12,
+		13, 14, 15, 16
+	};
+
+	mat4Print(t);
+
 	INFO("Compiling Shaders...");
 
 	// create and compile vertex shader
diff --git a/src/matrix-math.c b/src/matrix-math.c
new file mode 100644
index 0000000..f561bb0
--- /dev/null
+++ b/src/matrix-math.c
@@ -0,0 +1,67 @@
+#include "matrix-math.h"
+#include <math.h>
+#include <stdio.h>
+
+/**
+ * overwrites a 4x4 matrix with the identity matrix
+ */
+void mat4Identity(mat4 mat) {
+	for (int i = 0; i < 16; i++) {
+		mat[i] = (i % 4 == i / 4) ? 1 : 0;
+	}
+}
+
+/**
+ * copies a mat4 from src to dst
+ */
+void mat4Copy(mat4 src, mat4 dst) {
+	for (int i = 0; i < 16; i++) {
+		dst[i] = src[i];
+	}
+}
+
+/**
+ * sets all the values in a mat4 to zero
+ */
+void mat4Empty(mat4 mat) {
+	for (int i = 0; i < 16; i++) {
+		mat[i] = 0;
+	}
+}
+
+/**
+ * mutliplies A with B and stores the result in results
+ */
+void mat4Multiply(mat4 result, mat4 A, mat4 B) {
+	// if result is one of the arguments, modify copy instead of result directly
+	if (result == A || result == B) {
+		mat4 tempResult;
+		mat4Multiply(tempResult, A, B);
+		mat4Copy(tempResult, result);
+		return;
+	}
+
+	for (int i = 0; i < 16; i++) {
+		int col = i / 4;
+		int row = i % 4;
+		GLfloat* curr = &(result[i]);
+
+		*curr = 0;
+
+		for (int j = 0; j < 4; j++) {
+			*curr += A[row + j * 4] * B[j + col * 4];
+		}
+	}
+}
+
+/**
+ * prints a mat4 to the screen
+ */
+void mat4Print(mat4 m) {
+	for (int i = 0; i < 4; i++) {
+		for (int j = 0; j < 4; j++) {
+			printf("%.2f ", m[j * 4 + i]);
+		}
+		printf("\n");
+	}
+}
\ No newline at end of file
diff --git a/src/matrix-math.h b/src/matrix-math.h
new file mode 100644
index 0000000..d1a098b
--- /dev/null
+++ b/src/matrix-math.h
@@ -0,0 +1,23 @@
+#ifndef MATRIX_MATH_H
+#define MATRIX_MATH_H
+
+#include <GL/gl.h>	
+
+// TODO: figure out better type definition to avoid constant casting to GLfloat*
+// possibly typedef float mat4[16];
+
+/**
+ * !!! ALL matrices are in column major
+ */
+
+typedef GLfloat vec4[4];
+
+typedef GLfloat mat4[16];
+
+extern void mat4Identity(mat4 mat);
+extern void mat4Copy(mat4 src, mat4 dst);
+extern void mat4Empty(mat4 mat);
+extern void mat4Multiply(mat4 result, mat4 A, mat4 B);
+extern void mat4Print(mat4 m);
+
+#endif
\ No newline at end of file