+namespace {
+
+// Flip upside-down to compensate for different origin.
+template<class T>
+void vertical_flip(T *data, unsigned width, unsigned height)
+{
+ for (unsigned y = 0; y < height / 2; ++y) {
+ unsigned flip_y = height - y - 1;
+ for (unsigned x = 0; x < width; ++x) {
+ std::swap(data[y * width + x], data[flip_y * width + x]);
+ }
+ }
+}
+
+} // namespace
+