add utility functions

include/threepp/utils/ImageUtils.hpp

@@ -0,0 +1,26 @@
+
+#ifndef THREEPP_IMAGEUTILS_HPP
+#define THREEPP_IMAGEUTILS_HPP
+
+#include <vector>
+#include <algorithm>
+
+namespace threepp {
+
+    inline void convertBGRtoRGB(std::vector<unsigned char>& pixels) {
+        for (size_t i = 0; i < pixels.size(); i += 3) {
+            std::swap(pixels[i], pixels[i + 2]);
+        }
+    }
+
+    inline void flipImage(std::vector<unsigned char>& pixels, int channels, int w, int h) {
+        for (int line = 0; line != h / 2; ++line) {
+            std::swap_ranges(pixels.begin() + channels * w * line,
+                             pixels.begin() + channels * w * (line + 1),
+                             pixels.begin() + channels * w * (h - line - 1));
+        }
+    }
+
+}// namespace threepp
+
+#endif //THREEPP_IMAGEUTILS_HPP

src/CMakeLists.txt

@@ -170,6 +170,7 @@ set(publicHeaders
         "threepp/textures/Texture.hpp"
 
         "threepp/utils/BufferGeometryUtils.hpp"
+        "threepp/utils/ImageUtils.hpp"
         "threepp/utils/StringUtils.hpp"
 
         "threepp/lights/lights.hpp"