Add mat4_orbit.

__init__.py

@@ -182,6 +182,14 @@ mat4_lookat.argtypes = (
     _vec3_p, # position
     _vec3_p) # lookat
 
+mat4_orbit = _engine.rk_mat4_orbit
+mat4_orbit.argtypes = (
+    _mat4_p, # ret
+    _vec3_p, # origin
+    ctypes.c_float, # yaw
+    ctypes.c_float, # pitch
+    ctypes.c_float) # distance
+
 mat4_mul_vec3 = _engine.rk_mat4_mul_vec3
 mat4_mul_vec3.argtypes = (
     _vec3_p, # ret

cpp/math.cpp

@@ -64,7 +64,19 @@ void rk_mat4_lookat(
     rk_mat4 & ret,
     rk_vec3 const & position,
     rk_vec3 const & lookat) {
-    ret = glm::lookAtRH(position, lookat, glm::vec3(0.0f, 0.0f, 1.0f));
+    ret = glm::lookAtRH(position, lookat, vec3_up);
+}
+
+void rk_mat4_orbit(
+    rk_mat4 & ret,
+    rk_vec3 const & origin,
+    float const yaw,
+    float const pitch,
+    float const distance) {
+    ret = glm::translate(
+        glm::lookAtRH(glm::vec3(0.f, -distance, 0.f), vec3_origin, vec3_up) *
+            glm::mat4(glm::angleAxis(pitch, vec3_right) * glm::angleAxis(yaw, vec3_up)),
+        origin);
 }
 
 void rk_mat4_mul_vec3(

cpp/math.hpp

@@ -26,6 +26,11 @@ typedef glm::vec4 rk_vec4;
 typedef glm::mat3 rk_mat3;
 typedef glm::mat4 rk_mat4;
 
+#define vec3_right   (rk_vec3(1.f, 0.f, 0.f))
+#define vec3_forward (rk_vec3(0.f, 1.f, 0.f))
+#define vec3_up      (rk_vec3(0.f, 0.f, 1.f))
+#define vec3_origin  (rk_vec3(0.f, 0.f, 0.f))
+
 RK_EXPORT void rk_vec3_rotate(
     rk_vec3 & ret,
     rk_vec3 const & vec3,
@@ -64,6 +69,13 @@ RK_EXPORT void rk_mat4_lookat(
     rk_vec3 const & position,
     rk_vec3 const & lookat);
 
+RK_EXPORT void rk_mat4_orbit(
+    rk_mat4 & ret,
+    rk_vec3 const & origin,
+    float const yaw,
+    float const pitch,
+    float const distance);
+
 RK_EXPORT void rk_mat4_mul_vec3(
     rk_vec3 & ret,
     rk_mat4 const & a,