1 files changed, 129 insertions, 13 deletions

diff --git a/src/maths.c b/src/maths.c
index c1fab2a..3a7ecf1 100644
--- a/src/maths.c
+++ b/src/maths.c
@@ -1,27 +1,116 @@
 #include <celeritas.h>
 
 vec3 vec3_create(f32 x, f32 y, f32 z) { return (vec3){ x, y, z }; }
-
 vec3 vec3_add(vec3 u, vec3 v) { return (vec3){ .x = u.x + v.x, .y = u.y + v.y, .z = u.z + v.z }; }
+vec3 vec3_sub(vec3 a, vec3 b) { return (vec3){ a.x - b.x, a.y - b.y, a.z - b.z }; }
+vec3 vec3_mult(vec3 a, f32 s) { return (vec3){ a.x * s, a.y * s, a.z * s }; }
+vec3 vec3_div(vec3 a, f32 s) { return (vec3){ a.x / s, a.y / s, a.z / s }; }
+
+f32 vec3_len_squared(vec3 a) { return (a.x * a.x) + (a.y * a.y) + (a.z * a.z); }
+f32 vec3_len(vec3 a) { return sqrtf(vec3_len_squared(a)); }
+vec3 vec3_negate(vec3 a) { return (vec3){ -a.x, -a.y, -a.z }; }
+
+vec3 vec3_normalise(vec3 a) {
+  f32 length = vec3_len(a);
+  return vec3_div(a, length);
+}
+
+f32 vec3_dot(vec3 a, vec3 b) { return a.x * b.x + a.y * b.y + a.z * b.z; }
+
+vec3 vec3_cross(vec3 a, vec3 b) {
+  return (vec3){ .x = a.y * b.z - a.z * b.y, .y = a.z * b.x - a.x * b.z, .z = a.x * b.y - a.y * b.x };
+}
 
 vec4 vec4_create(f32 x, f32 y, f32 z, f32 w) { return (vec4){ x, y, z, w }; }
 
+f32 quat_dot(quat a, quat b) { return a.x * b.x + a.y * b.y + a.z * b.z + a.w * b.w; }
+
+quat quat_normalise(quat a) {
+  f32 length = sqrtf(quat_dot(a, a));  // same as len squared
+
+  return (quat){ a.x / length, a.y / length, a.z / length, a.w / length };
+}
+
+quat quat_from_axis_angle(vec3 axis, f32 angle, bool normalize) {
+  const f32 half_angle = 0.5f * angle;
+  f32 s = sinf(half_angle);
+  f32 c = cosf(half_angle);
+
+  quat q = (quat){ s * axis.x, s * axis.y, s * axis.z, c };
+  if (normalize) {
+    return quat_normalise(q);
+  }
+  return q;
+}
+
 mat4 mat4_ident() { return (mat4){ .data = { 1.0, 0., 0., 0., 0., 1., 0., 0., 0., 0., 1., 0., 0., 0., 0., 1.0 } }; }
 
-mat4 mat4_mult(mat4 lhs, mat4 rhs) {
+mat4 mat4_translation(vec3 position) {
+  mat4 out_matrix = mat4_ident();
+  out_matrix.data[12] = position.x;
+  out_matrix.data[13] = position.y;
+  out_matrix.data[14] = position.z;
+  return out_matrix;
+}
+
+mat4 mat4_scale(vec3 scale) {
   mat4 out_matrix = mat4_ident();
+  out_matrix.data[0] = scale.x;
+  out_matrix.data[5] = scale.y;
+  out_matrix.data[10] = scale.z;
+  return out_matrix;
+}
+
+// TODO: double check this
+mat4 mat4_rotation(quat rotation) {
+  mat4 out_matrix = mat4_ident();
+  quat n = quat_normalise(rotation);
+
+  out_matrix.data[0] = 1.0f - 2.0f * n.y * n.y - 2.0f * n.z * n.z;
+  out_matrix.data[1] = 2.0f * n.x * n.y - 2.0f * n.z * n.w;
+  out_matrix.data[2] = 2.0f * n.x * n.z + 2.0f * n.y * n.w;
+
+  out_matrix.data[4] = 2.0f * n.x * n.y + 2.0f * n.z * n.w;
+  out_matrix.data[5] = 1.0f - 2.0f * n.x * n.x - 2.0f * n.z * n.z;
+  out_matrix.data[6] = 2.0f * n.y * n.z - 2.0f * n.x * n.w;
+
+  out_matrix.data[8] = 2.0f * n.x * n.z - 2.0f * n.y * n.w;
+  out_matrix.data[9] = 2.0f * n.y * n.z + 2.0f * n.x * n.w;
+  out_matrix.data[10] = 1.0f - 2.0f * n.x * n.x - 2.0f * n.y * n.y;
+
+  return out_matrix;
+}
 
-  const f32* m1_ptr = lhs.data;
-  const f32* m2_ptr = rhs.data;
-  f32* dst_ptr = out_matrix.data;
+// mat4 mat4_mult(mat4 lhs, mat4 rhs) {
+//   mat4 out_matrix = mat4_ident();
 
-  for (i32 i = 0; i < 4; ++i) {
-    for (i32 j = 0; j < 4; ++j) {
-      *dst_ptr = m1_ptr[0] * m2_ptr[0 + j] + m1_ptr[1] * m2_ptr[4 + j] + m1_ptr[2] * m2_ptr[8 + j] +
-                 m1_ptr[3] * m2_ptr[12 + j];
-      dst_ptr++;
+//   const f32* m1_ptr = lhs.data;
+//   const f32* m2_ptr = rhs.data;
+//   f32* dst_ptr = out_matrix.data;
+
+//   for (i32 i = 0; i < 4; ++i) {
+//     for (i32 j = 0; j < 4; ++j) {
+//       *dst_ptr = m1_ptr[0] * m2_ptr[0 + j] + m1_ptr[1] * m2_ptr[4 + j] + m1_ptr[2] * m2_ptr[8 + j] +
+//                  m1_ptr[3] * m2_ptr[12 + j];
+//       dst_ptr++;
+//     }
+//     m1_ptr += 4;
+//   }
+
+//   return out_matrix;
+// }
+mat4 mat4_mult(mat4 lhs, mat4 rhs) {
+  mat4 out_matrix = mat4_ident();
+
+  for (i32 row = 0; row < 4; row++) {
+    for (i32 col = 0; col < 4; col++) {
+      f32 sum = 0;
+      for (i32 i = 0; i < 4; i++) {
+        // column-major: first matrix columns × second matrix rows
+        sum += lhs.data[row + i * 4] * rhs.data[i + col * 4];
+      }
+      out_matrix.data[row + col * 4] = sum;
     }
-    m1_ptr += 4;
   }
 
   return out_matrix;
@@ -39,5 +128,32 @@ mat4 mat4_perspective(f32 fov_radians, f32 aspect_ratio, f32 near_z, f32 far_z)
 }
 
 mat4 mat4_look_at(vec3 position, vec3 target, vec3 up) {
-  // TODO
-}
\ No newline at end of file
+  mat4 out_matrix;
+  vec3 z_axis;
+  z_axis.x = target.x - position.x;
+  z_axis.y = target.y - position.y;
+  z_axis.z = target.z - position.z;
+
+  z_axis = vec3_normalise(z_axis);
+  vec3 x_axis = vec3_normalise(vec3_cross(z_axis, up));
+  vec3 y_axis = vec3_cross(x_axis, z_axis);
+
+  out_matrix.data[0] = x_axis.x;
+  out_matrix.data[1] = y_axis.x;
+  out_matrix.data[2] = -z_axis.x;
+  out_matrix.data[3] = 0;
+  out_matrix.data[4] = x_axis.y;
+  out_matrix.data[5] = y_axis.y;
+  out_matrix.data[6] = -z_axis.y;
+  out_matrix.data[7] = 0;
+  out_matrix.data[8] = x_axis.z;
+  out_matrix.data[9] = y_axis.z;
+  out_matrix.data[10] = -z_axis.z;
+  out_matrix.data[11] = 0;
+  out_matrix.data[12] = -vec3_dot(x_axis, position);
+  out_matrix.data[13] = -vec3_dot(y_axis, position);
+  out_matrix.data[14] = vec3_dot(z_axis, position);
+  out_matrix.data[15] = 1.0f;
+
+  return out_matrix;
+}