+#include <stddef.h>
+
+#include "geometry.h"
+
+Transform identity() {
+ return (Transform) { .a1 = 1.0f, .a2 = 0.0f, .a3 = 0.0f, .a4 = 0.0f,
+ .b1 = 0.0f, .b2 = 1.0f, .b3 = 0.0f, .b4 = 0.0f,
+ .c1 = 0.0f, .c2 = 0.0f, .c3 = 1.0f, .c4 = 0.0f,
+ .d1 = 0.0f, .d2 = 0.0f, .d3 = 0.0f, .d4 = 1.0f };
+}
+
+void multiply(Transform* transform, Transform by) {
+ GLfloat* a = (GLfloat*) &by;
+ GLfloat* b = (GLfloat*) transform;
+
+ for (size_t row = 0; row < 4; ++row) {
+ for (size_t col = 0; col < 4; ++col) {
+ b[(row * 4) + col] =
+ a[(row * 4) + 0] * b[(0 * 4) + col]
+ + a[(row * 4) + 1] * b[(1 * 4) + col]
+ + a[(row * 4) + 2] * b[(2 * 4) + col]
+ + a[(row * 4) + 3] * b[(3 * 4) + col];
+ }
+ }
+}
+
+void translate(Transform* transform, Vector3D vec) {
+ multiply(transform, (Transform) { .a1 = 1.0f, .a2 = 0.0f, .a3 = 0.0f, .a4 = vec.x,
+ .b1 = 0.0f, .b2 = 1.0f, .b3 = 0.0f, .b4 = vec.y,
+ .c1 = 0.0f, .c2 = 0.0f, .c3 = 1.0f, .c4 = vec.z,
+ .d1 = 0.0f, .d2 = 0.0f, .d3 = 0.0f, .d4 = 1.0f });
+}
+
+Vector3D translationOf(Transform transform) {
+ return (Vector3D) { transform.a4, transform.b4, transform.c4 };
+}