--- a/Renderer/Engine/sys.cc	Sun Dec 06 01:48:18 2009 +0900
+++ b/Renderer/Engine/sys.cc	Sun Dec 06 07:40:26 2009 +0900
@@ -241,3 +241,24 @@
   xyz[1] += y;
   xyz[2] += z;
 }
+
+/**                                                                                       
+ *  ベクトルに行列を乗算する                                                              
+ * @param[out] v vector (float[4])                                                        
+ * @param[in] m matrix (float[16])                                                        
+ */
+void
+ApplyMatrix(float *v, float *m)
+{
+  float t[4];
+
+  t[0] = v[0];
+  t[1] = v[1];
+  t[2] = v[2];
+  t[3] = v[3];
+
+  for (int i = 0; i < 4; i++) {
+    v[i] = t[0]*m[i] + t[1]*m[i+4] + t[2]*m[i+8] + t[3]*m[i+12];
+  }
+}
+