From 28eb4cbfc35613b4e9cac0e4e6749f1f2460031e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lo=C3=AFc=20GUEZO?= <loicguezo@gmail.com>
Date: Mon, 31 Mar 2025 15:18:41 +0200
Subject: [PATCH] feat(matrix3): add inv function.

---
 include/math/matrix3.h |  1 +
 src/math/matrix3.c     | 22 +++++++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/math/matrix3.h b/include/math/matrix3.h
index 378d869..ba128dc 100644
--- a/include/math/matrix3.h
+++ b/include/math/matrix3.h
@@ -15,5 +15,6 @@ Mat3 mat3Scl(Mat3 m, float scalar);
 Mat3 mat3Mul(Mat3 m1, Mat3 m2);
 Mat3 mat3Tpo(Mat3 m);
 float mat3Det(Mat3 m);
+Mat3 mat3Inv(Mat3 m);
 
 #endif // MATRIX_H
\ No newline at end of file
diff --git a/src/math/matrix3.c b/src/math/matrix3.c
index ea6e286..61bfe0f 100644
--- a/src/math/matrix3.c
+++ b/src/math/matrix3.c
@@ -1,6 +1,5 @@
 #include "math/matrix3.h"
 #include <string.h>
-#include <math.h>
 
 Mat3 mat3(float arr[9]) {
     Mat3 mat;
@@ -87,4 +86,25 @@ float mat3Det(Mat3 m) {
     return m.m[0] * (m.m[4] * m.m[8] - m.m[5] * m.m[7]) -
            m.m[1] * (m.m[3] * m.m[8] - m.m[5] * m.m[6]) +
            m.m[2] * (m.m[3] * m.m[7] - m.m[4] * m.m[6]);
+}
+
+Mat3 mat3Inv(Mat3 m) {
+    Mat3 inv;
+    float det = mat3Det(m);
+    if (det == 0) return mat3Ity();
+
+    float invDet = 1.0f / det;
+
+    // ???
+    inv.m[0] =  (m.m[4] * m.m[8] - m.m[5] * m.m[7]) * invDet;
+    inv.m[1] = -(m.m[1] * m.m[8] - m.m[2] * m.m[7]) * invDet;
+    inv.m[2] =  (m.m[1] * m.m[5] - m.m[2] * m.m[4]) * invDet;
+    inv.m[3] = -(m.m[3] * m.m[8] - m.m[5] * m.m[6]) * invDet;
+    inv.m[4] =  (m.m[0] * m.m[8] - m.m[2] * m.m[6]) * invDet;
+    inv.m[5] = -(m.m[0] * m.m[5] - m.m[2] * m.m[3]) * invDet;
+    inv.m[6] =  (m.m[3] * m.m[7] - m.m[4] * m.m[6]) * invDet;
+    inv.m[7] = -(m.m[0] * m.m[7] - m.m[1] * m.m[6]) * invDet;
+    inv.m[8] =  (m.m[0] * m.m[4] - m.m[1] * m.m[3]) * invDet;
+
+    return inv;
 }
\ No newline at end of file