Add homogeneous scale transformation

Add function to generate homogeneous 3 dimensional scale transformation
matrices.

rtengine/homogeneouscoordinates.cc

@@ -147,6 +147,23 @@ Matrix<T> rotationMatrix(double radians, Axis axis)
     return matrix;
 }
 
+template <typename T>
+Matrix<T> scaleMatrix(T x, T y, T z)
+{
+    Matrix<T> matrix;
+
+    for (int i = 0; i < 4; i++) {
+        matrix[i].fill(0);
+    }
+
+    matrix[0][0] = x;
+    matrix[1][1] = y;
+    matrix[2][2] = z;
+    matrix[3][3] = 1;
+
+    return matrix;
+}
+
 template <typename T>
 Matrix<T> translationMatrix(T x, T y, T z)
 {

rtengine/homogeneouscoordinates.h

@@ -53,6 +53,15 @@ Matrix<T> projectionMatrix(T location, Axis normal);
 template <typename T>
 Matrix<T> rotationMatrix(T radians, Axis axis);
 
+/**
+ * Creates a 3 dimensional transformation matrix for scaling.
+ * @param x Scale in x-direction
+ * @param y Scale in y-direction
+ * @param z Scale in z-direction
+ */
+template <typename T>
+Matrix<T> scaleMatrix(T x, T y, T z);
+
 /**
  * Creates a 3 dimensional transformation matrix for translation.
  * @param x Translation in the the x-direction.