ensure correct endianness for decoding and encoding 16 bit raw data using LodePNG

src/ACGL/OpenGL/Data/TextureDataLoadStore.cc

@@ -15,6 +15,7 @@
 #include <cstdio>
 #include <ctime>
 
+#include <stdexcept>
 #include <fstream>
 #include "lodepng/lodepng.h"
 #include "rgbe/rgbe.hh"
@@ -163,34 +164,52 @@ bool saveScreenshotWithDate(const std::string& _prefix, const std::string& _file
 //                                                                           library specific load
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
+struct LodepngFile
+{
+public:
+    LodepngFile(const std::string& _filename)
+    {
+        unsigned int errorCode = lodepng_load_file(&mData, &mSize, _filename.c_str());
+        if(errorCode)
+        {
+            std::stringstream errorMsg;
+            errorMsg << "LodePNG error while loading file " << _filename << " - " << errorCode << ": " << lodepng_error_text(errorCode);
+            mData = nullptr;
+            throw std::runtime_error(errorMsg.str());
+        }
+    }
+
+    ~LodepngFile()
+    {
+        free(mData);
+    }
+
+    unsigned char* mData;
+    size_t mSize;
+};
+
 SharedTextureData loadTextureDataFromLodepng(const std::string &_filename)
 {
     SharedTextureData data;
 
     unsigned int errorCode;
     unsigned int width, height;
-    unsigned char* png;
-    size_t pngsize;
     LodePNGState state;
 
     // Load the PNG file from disk
-
     lodepng_state_init(&state);
 
-    errorCode = lodepng_load_file(&png, &pngsize, _filename.c_str());
-    if(errorCode)
+    try
     {
-        ACGL::Utils::error() << "LodePNG error while loading file " << _filename << " - " << errorCode << ": " << lodepng_error_text(errorCode) << std::endl;
-        return data;
-    }
+        LodepngFile lodepngFile(_filename);
 
         // Extract metadata (bit depth, color type)
-
-    errorCode = lodepng_inspect(&width, &height, &state, png, pngsize);
+        errorCode = lodepng_inspect(&width, &height, &state, lodepngFile.mData, lodepngFile.mSize);
         if(errorCode)
         {
-        ACGL::Utils::error() << "LodePNG error " << errorCode << ": " << lodepng_error_text(errorCode) << std::endl;
-        return data;
+            std::stringstream errorMsg;
+            errorMsg << "LodePNG error " << errorCode << ": " << lodepng_error_text(errorCode);
+            throw std::runtime_error(errorMsg.str());
         }
 
         unsigned int bitdepth = state.info_png.color.bitdepth;
@@ -208,28 +227,32 @@ SharedTextureData loadTextureDataFromLodepng(const std::string &_filename)
         GLenum glType = 0;
         if(bitdepth ==  8) glType = GL_UNSIGNED_BYTE;
         if(bitdepth == 16) glType = GL_UNSIGNED_SHORT;
-    if(bitdepth == 32) glType = GL_UNSIGNED_INT;
 
         if(channels == 0 || glFormat == 0 || glType == 0)
         {
-        ACGL::Utils::error() << "Could not load " << _filename << ": " << "unsupported bit depth or format" << std::endl;
-        return data;
+            std::stringstream errorMsg;
+            errorMsg << "Could not load " << _filename << ": " << "unsupported bit depth or format";
+            throw std::runtime_error(errorMsg.str());
         }
 
         // Decode the image
-
         unsigned char* image;
-    errorCode = lodepng_decode_memory(&image, &width, &height, png, pngsize, colorType, bitdepth);
+        errorCode = lodepng_decode_memory(&image, &width, &height, lodepngFile.mData, lodepngFile.mSize, colorType, bitdepth);
         if(errorCode)
         {
-        ACGL::Utils::error() << "LodePNG error while loading file " << _filename << " - " << errorCode << ": " << lodepng_error_text(errorCode) << std::endl;
-        return data;
+            std::stringstream errorMsg;
+            errorMsg << "LodePNG error while decoding file " << _filename << " - " << errorCode << ": " << lodepng_error_text(errorCode);
+            throw std::runtime_error(errorMsg.str());
         }
 
-    free(png);
+        // LodePNG decodes 16 bit PNGs in big endian format ==> Convert
+#ifndef ACGL_BIG_ENDIAN
+        if(bitdepth == 16)
+            for(int i = 0; i < (width * height * channels * 2); i += 2)
+                std::swap(image[i], image[i+1]);
+#endif
 
         // Wrap the data in a TextureData object
-
         data = SharedTextureData(new TextureData());
         data->setData((GLubyte*)image);
         data->setWidth(width);
@@ -239,6 +262,11 @@ SharedTextureData loadTextureDataFromLodepng(const std::string &_filename)
 
         // Flip
         data->flipVertically();
+    }
+    catch(std::runtime_error& error)
+    {
+        ACGL::Utils::error() << error.what() << std::endl;
+    }
 
     return data;
 }
@@ -626,6 +654,12 @@ bool saveTextureDataToLodepng( const SharedTextureData &_data, const std::string
         return false;
     }
 
+    // LodePNG expects 16 bit image data in big endian format ==> convert
+#ifndef ACGL_BIG_ENDIAN
+        if(channelBitCount == 16)
+            for(int i = 0; i < _data->getWidth() * _data->getHeight() * _data->getNumberOfChannels() * 2; i += 2)
+                std::swap(processedData[i], processedData[i+1]);
+#endif
 
     LodePNGColorType colorType;
     if (channelCount == 1) colorType = LCT_GREY;