quat: create view wmatrix with quaternion helper

include/cglm/quat.h

@@ -39,6 +39,8 @@
 
 #include "common.h"
 #include "vec4.h"
+#include "mat4.h"
+#include "mat3.h"
 
 #ifdef CGLM_SSE_FP
 #  include "simd/sse2/quat.h"
@@ -578,4 +580,29 @@ glm_quat_slerp(versor from, versor to, float t, versor dest) {
   glm_vec4_scale(q1, 1.0f / sinTheta, dest);
 }
 
+CGLM_INLINE
+void
+glm_mat4_mulv(mat4 m, vec4 v, vec4 dest);
+
+/*!
+ * @brief creates view matrix using quaternion as camera orientation
+ *
+ * @param[in]   eye   eye
+ * @param[in]   ori   orientation in world space as quaternion
+ * @param[out]  dest  view matrix
+ */
+CGLM_INLINE
+void
+glm_quat_look(vec3 eye, versor ori, mat4 dest) {
+  vec4 t;
+
+  /* orientation */
+  glm_quat_mat4t(ori, dest);
+
+  /* translate */
+  glm_vec4(eye, 1.0f, t);
+  glm_mat4_mulv(dest, t, t);
+  glm_vec_flipsign_to(t, dest[3]);
+}
+
 #endif /* cglm_quat_h */

test/src/test_quat.c

@@ -18,8 +18,9 @@ test_quat_mul_raw(versor p, versor q, versor dest) {
 
 void
 test_quat(void **state) {
-  mat4   inRot, outRot;
+  mat4   inRot, outRot, view1, view2;
   versor inQuat, outQuat, q3, q4;
+  vec3   eye;
   int    i;
 
   for (i = 0; i < 1000; i++) {
@@ -35,4 +36,16 @@ test_quat(void **state) {
 
     test_assert_quat_eq(q3, q4);
   }
+
+  /* test lookat */
+  test_rand_vec3(eye);
+  glm_quatv(q3, glm_rad(-90.0f), GLM_YUP);
+
+  /* now X axis must be forward axis, Z must be right axis */
+  glm_look(eye, GLM_XUP, GLM_YUP, view1);
+
+  /* create view matrix with quaternion */
+  glm_quat_look(eye, q3, view2);
+
+  test_assert_mat4_eq2(view1, view2, 0.000009);
 }