diff --git a/etk/math/Matrix4.cpp b/etk/math/Matrix4.cpp
index 1407068..0ac745e 100644
--- a/etk/math/Matrix4.cpp
+++ b/etk/math/Matrix4.cpp
@@ -31,19 +31,13 @@ void etk::Matrix4::Translate(etk::Vector3D<float>& vect)
 }
 
 
-etk::Matrix4 etk::matPerspective(float fovx, float aspect, float zNear, float zFar)
+etk::Matrix4 etk::matFrustum(float xmin, float xmax, float ymin, float ymax, float zNear, float zFar)
 {
 	etk::Matrix4 tmp;
 	for(int32_t iii=0; iii<4*4 ; iii++) {
 		tmp.m_mat[iii] = 0;
 	}
 	
-	float xmax = zNear * tanf(fovx * M_PI / 360.0);
-	float xmin = -xmax;
-	
-	float ymin = xmin / aspect;
-	float ymax = xmax / aspect;
-	
 	//  0  1  2  3
 	//  4  5  6  7
 	//  8  9 10 11
@@ -60,6 +54,18 @@ etk::Matrix4 etk::matPerspective(float fovx, float aspect, float zNear, float zF
 	return tmp;
 }
 
+etk::Matrix4 etk::matPerspective(float fovx, float aspect, float zNear, float zFar)
+{
+	//TK_DEBUG("drax perspective: fovx=" << fovx << "->" << aspect << "  " << zNear << "->" << zFar);
+	float xmax = zNear * tanf(fovx/2.0);
+	float xmin = -xmax;
+	
+	float ymin = xmin / aspect;
+	float ymax = xmax / aspect;
+	//TK_DEBUG("drax perspective: " << xmin << "->" << xmax << " & " << ymin << "->" << ymax << " " << zNear << "->" << zFar);
+	return etk::matFrustum(xmin, xmax, ymin, ymax, zNear, zFar);
+}
+
 etk::Matrix4 etk::matOrtho(float left, float right, float bottom, float top, float nearVal, float farVal)
 {
 	etk::Matrix4 tmp;
diff --git a/etk/math/Matrix4.h b/etk/math/Matrix4.h
index 30b6f4a..6c0a499 100644
--- a/etk/math/Matrix4.h
+++ b/etk/math/Matrix4.h
@@ -291,7 +291,8 @@ namespace etk
 			 */
 			Matrix4 Invert(void);
 	};
-	Matrix4 matPerspective(float fovx, float aspect, float zNear, float zFar);
+	Matrix4 matFrustum(float xmin, float xmax, float ymin, float ymax, float zNear, float zFar);
+	Matrix4 matPerspective(float foxy, float aspect, float zNear, float zFar);
 	Matrix4 matOrtho(float left, float right, float bottom, float top, float nearVal, float farVal);
 	Matrix4 matTranslate(etk::Vector3D<float> vect);
 	Matrix4 matScale(etk::Vector3D<float> vect);