refract

include/cglm/vec3.h

@@ -80,9 +80,9 @@
    CGLM_INLINE void  glm_vec3_smoothinterpc(vec3 from, vec3 to, float t, vec3 dest);
    CGLM_INLINE void  glm_vec3_swizzle(vec3 v, int mask, vec3 dest);
    CGLM_INLINE void  glm_vec3_make(float * restrict src, vec3 dest);
-   CGLM_INLINE void  glm_vec3_reflect(vec3 I, vec3 N, vec3 dest);
-   CGLM_INLINE void  glm_vec3_refract(vec3 I, vec3 N, float ior, vec3 dest);
    CGLM_INLINE void  glm_vec3_faceforward(vec3 N, vec3 I, vec3 Nref, vec3 dest);
+   CGLM_INLINE void  glm_vec3_reflect(vec3 I, vec3 N, vec3 dest);
+   CGLM_INLINE void  glm_vec3_refract(vec3 I, vec3 N, float eta, vec3 dest);
 
  Convenient:
    CGLM_INLINE void  glm_cross(vec3 a, vec3 b, vec3 d);
@@ -1205,6 +1205,28 @@ glm_vec3_make(const float * __restrict src, vec3 dest) {
   dest[2] = src[2];
 }
 
+/*!
+ * @brief a vector pointing in the same direction as another
+ *
+ * orients a vector to point away from a surface as defined by its normal
+ *
+ * @param[in] N      vector to orient.
+ * @param[in] I      incident vector
+ * @param[in] Nref   reference vector
+ * @param[out] dest  oriented vector, pointing away from the surface.
+ */
+CGLM_INLINE
+void
+glm_vec3_faceforward(vec3 N, vec3 I, vec3 Nref, vec3 dest) {
+  if (glm_vec3_dot(I, Nref) < 0.0f) {
+    /* N is facing away from I */
+    glm_vec3_copy(N, dest);
+  } else {
+    /* N is facing towards I, negate it */
+    glm_vec3_negate_to(N, dest);
+  }
+}
+
 /*!
  * @brief reflection vector using an incident ray and a surface normal
  *
@@ -1221,25 +1243,32 @@ glm_vec3_reflect(vec3 I, vec3 N, vec3 dest) {
 }
 
 /*!
- * @brief a vector pointing in the same direction as another
+ * @brief refraction vector using entering ray, surface normal and refraction index
  *
- * orients a vector to point away from a surface as defined by its normal
+ * if the angle between the entering ray I and the surface normal N is too great
+ * for a given refraction index, the return value is zero
  *
- * @param[in] N      vector to orient.
- * @param[in] I      incident vector
- * @param[in] Nref   reference vector
- * @param[out] dest  oriented vector, pointing away from the surface.
+ * @param[in]  I    normalized incident vector
+ * @param[in]  N    normalized normal vector
+ * @param[in]  eta  ratio of indices of refraction
+ * @param[out] dest refraction result
  */
 CGLM_INLINE
-void 
-glm_vec3_faceforward(vec3 N, vec3 I, vec3 Nref, vec3 dest) {
-  if (glm_vec3_dot(I, Nref) < 0.0f) {
-    /* N is facing away from I */
-    glm_vec3_copy(N, dest);
-  } else {
-    /* N is facing towards I, negate it */
-    glm_vec3_negate_to(N, dest);
+void
+glm_vec3_refract(vec3 I, vec3 N, float eta, vec3 dest) {
+  float ndi, eni, k;
+
+  ndi = glm_vec3_dot(N, I);
+  eni = eta * ndi;
+  k   = eta * eta + eni * eni;
+
+  if (k > 1.0f) {
+    glm_vec3_zero(dest);
+    return;
   }
+
+  glm_vec3_scale(I, eta, dest);
+  glm_vec3_mulsubs(N, eni + sqrt(1.0f - k), dest);
 }
 
 #endif /* cglm_vec3_h */