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OpenTGA.cpp

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#include <algorithm>
#include "Debug.h"
#include "Open.h"
#include "SimpleImage.h"
#include "Utility.h"


namespace corona {

  Image* OpenTGA(File* file) {
    COR_GUARD("OpenTGA");

    // read header
    byte header[18];
    if (file->read(header, 18) != 18) {
      return 0;
    }

    // decode header
    int id_length        = header[0];
    int cm_type          = header[1];
    int image_type       = header[2];
    //int cm_first         = read16_le(header + 3);
    int cm_length        = read16_le(header + 5);
    int cm_entry_size    = header[7];  // in bits
    //int x_origin         = read16_le(header + 8);
    //int y_origin         = read16_le(header + 10);
    int width            = read16_le(header + 12);
    int height           = read16_le(header + 14);
    int pixel_depth      = header[16];
    int image_descriptor = header[17];
    
    bool mirrored = (image_descriptor & (1 << 4)) != 0;  // left-to-right?
    bool flipped  = (image_descriptor & (1 << 5)) == 0;  // bottom-to-top?

    /*
     * image types
     * 0  = no image data
     * 1  = uncompressed, color-mapped
     * 2  = uncompressed, true-color
     * 3  = uncompressed, black and white
     * 9  = RLE, color-mapped
     * 10 = RLE, true-color
     * 11 = RLE, black and white
     */

    // make sure we support the image
    if (image_type != 2 || (pixel_depth != 24 && pixel_depth != 32)) {
      return 0;
    }

    // skip image id
    byte unused[255];
    if (file->read(unused, id_length) != id_length) {
      return 0;
    }

    // skip color map
    if (cm_type != 0) {
      // allocate color map
      int cm_entry_bytes = (cm_entry_size + 7) / 8;
      int cm_size = cm_entry_bytes * cm_length;
      auto_array<byte> color_map(new byte[cm_size]);
      if (file->read(color_map, cm_size) != cm_size) {
        return 0;
      }
    }

    // read image data
    PixelFormat format;
    auto_array<byte> pixels;
    if (pixel_depth == 24) {

      COR_LOG("24-bit image");

      format = PF_B8G8R8;
      int image_size = width * height * 3;
      pixels = new byte[image_size];
      if (file->read(pixels, image_size) != image_size) {
        return 0;
      }

    } else if (pixel_depth == 32) {

      COR_LOG("32-bit image");

      format = PF_B8G8R8A8;
      int image_size = width * height * 4;
      pixels = new byte[image_size];
      if (file->read(pixels, image_size) != image_size) {
        return 0;
      }

    } else {
      return 0;
    }

    // reverse each row
    if (mirrored) {
      COR_LOG("Image is mirrored");

      const int bpp = pixel_depth / 8;  // bytes per pixel
      for (int y = 0; y < height; ++y) {

        // points to the first pixel of the row
        byte* start = pixels.get() + y * width * bpp;
        // points to the last pixel of the row
        byte* end   = start + (width - 1) * bpp;

        while (start < end) {
          for (int b = 0; b < bpp; ++b) {
            std::swap(start[b], end[b]);
          }
          start += bpp;
          end   -= bpp;
        }
      }
    }

    // reverse rows as a whole
    if (flipped) {
      COR_LOG("Image is flipped");

      const int bpp = pixel_depth / 8;  // bytes per pixel
      const int row_size = width * bpp;
      auto_array<byte> temp(new byte[row_size]);  // for the swap

      // points to the beginning of the first row
      byte* start = pixels.get();

      // points to the beginning of the last row
      byte* end   = start + (height - 1) * width * bpp;

      while (start < end) {
        memcpy(temp.get(), start,      row_size);
        memcpy(start,      end,        row_size);
        memcpy(end,        temp.get(), row_size);

        start += row_size;
        end   -= row_size;
      }
    }

    return new SimpleImage(width, height, format, pixels.release());
  }

}

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