compose tga

#include <iostream>
#include "TargaImage.h"

#define MAX(a, b) (a > b ? a : b)
#define MIN(a, b) (a < b ? a : b)
#define CLIP(c) (MIN(MAX(0, c), 255))

int main(int c, char **v) {
  if (c != 3) {
    std::cerr << "Syntax: " << v[0] << " <original.tga> <compose.tga>" << std::endl;
    return 42;
  }
  TargaImage *image = TargaImage::readImage(v[1]);
  unsigned char *p1 = image->pixels();
  unsigned int h = image->height();
  unsigned int w = image->width();

  TargaImage *out = TargaImage::blankImage(w, h * 6);
  unsigned char *p2 = out->pixels();

  for (unsigned int i = 0; i < w * h * 6; i++) {
    unsigned int ii = i % (w * h); // Original pixel array offset
    unsigned char r = p1[ii * 4], g = p1[ii * 4 + 1], b = p1[ii * 4 + 2];

    p2[i * 4 + 3] = p1[ii * 4 + 3]; // Always set alpha to original alpha
    switch(i / w / h) {
      case 0: // Lighten
        p2[i * 4]     = CLIP(r + 50);
        p2[i * 4 + 1] = CLIP(g + 50);
        p2[i * 4 + 2] = CLIP(b + 50);
        break;
      case 1: // Darken
        p2[i * 4]     = CLIP(r - 50);
        p2[i * 4 + 1] = CLIP(g - 50);
        p2[i * 4 + 2] = CLIP(b - 50);
        break;
      case 2: // Low Contrast
        p2[i * 4]     = CLIP(r / 2);
        p2[i * 4 + 1] = CLIP(g / 2);
        p2[i * 4 + 2] = CLIP(b / 2);
        break;
      case 3: // High Contrast
        p2[i * 4]     = CLIP(r * 2);
        p2[i * 4 + 1] = CLIP(g * 2);
        p2[i * 4 + 2] = CLIP(b * 2);
        break;
      case 4: // Low Contrast
        p2[i * 4] = p2[i * 4 + 1] = p2[i * 4 + 2] = CLIP(r * 0.299 + g * 0.587 + b * 0.114);
        break;
      case 5: // Low Contrast
        p2[i * 4]     = CLIP(r * 0.393 + g * 0.769 + b * 0.189);
        p2[i * 4 + 1] = CLIP(r * 0.349 + g * 0.686 + b * 0.168);
        p2[i * 4 + 2] = CLIP(r * 0.272 + g * 0.534 + b * 0.131);
        break;
    }
  }

  out->write(v[2]);

  return 0;
}