added quat_slerp_longest

docs/source/quat.rst

@@ -55,6 +55,7 @@ Functions:
 #. :c:func:`glm_quat_lerp`
 #. :c:func:`glm_quat_nlerp`
 #. :c:func:`glm_quat_slerp`
+#. :c:func:`glm_quat_slerp_longest`
 #. :c:func:`glm_quat_look`
 #. :c:func:`glm_quat_for`
 #. :c:func:`glm_quat_forp`
@@ -351,6 +352,17 @@ Functions documentation
       | *[in]*  **t**     interpolant (amount) clamped between 0 and 1
       | *[out]* **dest**  result quaternion
 
+.. c:function:: void glm_quat_slerp_longest(versor q, versor r, float  t, versor dest)
+    
+    | interpolates between two quaternions
+    | using spherical linear interpolation (SLERP) and always takes the longest path
+    
+    Parameters:
+      | *[in]*  **from**  from
+      | *[in]*  **to**    to
+      | *[in]*  **t**     interpolant (amount) clamped between 0 and 1
+      | *[out]* **dest**  result quaternion
+
 .. c:function:: void  glm_quat_look(vec3 eye, versor ori, mat4 dest)
 
     | creates view matrix using quaternion as camera orientation

include/cglm/call/quat.h

@@ -133,6 +133,10 @@ CGLM_EXPORT
 void
 glmc_quat_slerp(versor q, versor r, float t, versor dest);
 
+CGLM_EXPORT
+void
+glmc_quat_slerp_longest(versor q, versor r, float t, versor dest);
+
 CGLM_EXPORT
 void
 glmc_quat_look(vec3 eye, versor ori, mat4 dest);

include/cglm/quat.h

@@ -39,6 +39,7 @@
    CGLM_INLINE void glm_quat_lerp(versor from, versor to, float t, versor dest);
    CGLM_INLINE void glm_quat_lerpc(versor from, versor to, float t, versor dest);
    CGLM_INLINE void glm_quat_slerp(versor q, versor r, float t, versor dest);
+   CGLM_INLINE void glm_quat_slerp_longest(versor q, versor r, float t, versor dest);
    CGLM_INLINE void glm_quat_nlerp(versor q, versor r, float t, versor dest);
    CGLM_INLINE void glm_quat_look(vec3 eye, versor ori, mat4 dest);
    CGLM_INLINE void glm_quat_for(vec3 dir, vec3 fwd, vec3 up, versor dest);
@@ -742,6 +743,52 @@ glm_quat_slerp(versor from, versor to, float t, versor dest) {
   glm_vec4_scale(q1, 1.0f / sinTheta, dest);
 }
 
+/*!
+ * @brief interpolates between two quaternions
+ *        using spherical linear interpolation (SLERP) and always takes the long path
+ *
+ * @param[in]   from  from
+ * @param[in]   to    to
+ * @param[in]   t     amout
+ * @param[out]  dest  result quaternion
+ */
+CGLM_INLINE
+void
+glm_quat_slerp_longest(versor from, versor to, float t, versor dest) {
+  CGLM_ALIGN(16) vec4 q1, q2;
+  float cosTheta, sinTheta, angle;
+
+  cosTheta = glm_quat_dot(from, to);
+  glm_quat_copy(from, q1);
+
+  if (fabsf(cosTheta) >= 1.0f) {
+    glm_quat_copy(q1, dest);
+    return;
+  }
+
+//NOTE THAT ONLY THIS CHANGED
+  if (!(cosTheta < 0.0f)) {
+    glm_vec4_negate(q1);
+    cosTheta = -cosTheta;
+  }
+
+  sinTheta = sqrtf(1.0f - cosTheta * cosTheta);
+
+  /* LERP to avoid zero division */
+  if (fabsf(sinTheta) < 0.001f) {
+    glm_quat_lerp(from, to, t, dest);
+    return;
+  }
+
+  /* SLERP */
+  angle = acosf(cosTheta);
+  glm_vec4_scale(q1, sinf((1.0f - t) * angle), q1);
+  glm_vec4_scale(to, sinf(t * angle), q2);
+
+  glm_vec4_add(q1, q2, q1);
+  glm_vec4_scale(q1, 1.0f / sinTheta, dest);
+}
+
 /*!
  * @brief creates view matrix using quaternion as camera orientation
  *

include/cglm/struct/quat.h

@@ -37,6 +37,7 @@
    CGLM_INLINE versors glms_quat_lerpc(versors from, versors to, float t)
    CGLM_INLINE versors glms_quat_nlerp(versors from, versors to, float t)
    CGLM_INLINE versors glms_quat_slerp(versors from, versors to, float t)
+   CGLM_INLINE versors glms_quat_slerp_longest(versors from, versors to, float t)
    CGLM_INLINE mat4s.  glms_quat_look(vec3s eye, versors ori)
    CGLM_INLINE versors glms_quat_for(vec3s dir, vec3s fwd, vec3s up)
    CGLM_INLINE versors glms_quat_forp(vec3s from, vec3s to, vec3s fwd, vec3s up)
@@ -457,6 +458,23 @@ glms_quat_(slerp)(versors from, versors to, float t) {
   return dest;
 }
 
+/*!
+ * @brief interpolates between two quaternions
+ *        using spherical linear interpolation (SLERP) and always takes the longest path
+ *
+ * @param[in]   from  from
+ * @param[in]   to    to
+ * @param[in]   t     amout
+ * @returns result quaternion
+ */
+CGLM_INLINE
+versors
+glms_quat_(slerp_longest)(versors from, versors to, float t) {
+  versors dest;
+  glm_quat_slerp_longest(from.raw, to.raw, t, dest.raw);
+  return dest;
+}
+
 /*!
  * @brief creates view matrix using quaternion as camera orientation
  *

src/quat.c

@@ -188,6 +188,12 @@ glmc_quat_slerp(versor from, versor to, float t, versor dest) {
   glm_quat_slerp(from, to, t, dest);
 }
 
+CGLM_EXPORT
+void
+glmc_quat_slerp_longest(versor from, versor to, float t, versor dest) {
+  glm_quat_slerp_longest(from, to, t, dest);
+}
+
 CGLM_EXPORT
 void
 glmc_quat_look(vec3 eye, versor ori, mat4 dest) {