extract fovy and aspect for perpective matrix

include/cglm/cam.h

@@ -426,6 +426,31 @@ glm_persp_decomp_near(mat4 proj, float * __restrict nearVal) {
   *nearVal = proj[3][2] / (proj[2][2] - 1);
 }
 
+/*!
+ * @brief returns field of view angle along the Y-axis (in radians)
+ *
+ * if you need to degrees, use glm_deg to convert it or use this:
+ * fovy_deg = glm_deg(glm_persp_fovy(projMatrix))
+ *
+ * @param[in] proj perspective projection matrix
+ */
+CGLM_INLINE
+float
+glm_persp_fovy(mat4 proj) {
+  return 2.0 * atan(1.0 / proj[1][1]);
+}
+
+/*!
+ * @brief returns aspect ratio of perspective projection
+ *
+ * @param[in] proj perspective projection matrix
+ */
+CGLM_INLINE
+float
+glm_persp_aspect(mat4 proj) {
+  return proj[1][1] / proj[0][0];
+}
+
 /*!
  * @brief extracts view frustum planes
  *