//============================================================================
// showppm.cpp
//============================================================================
#include <stdio.h>
#include <stdlib.h>
#include <GL/glut.h>

GLubyte *FBuffer;
int Width, Height;

void ReadPPM(char* PPMfileName) // Doesn't read ascii ppm files (P3) yet
{
  // LOAD FROM A BINARY .PPM FILE  
  int Color;
  int NumComponents;
  char Buffer[100];
  FILE* FilePtr = fopen(PPMfileName, "rb");
  if (FilePtr==NULL)
     { fprintf(stderr, "ERROR: unable to open %s!\n",PPMfileName); exit(1); }
  fgets(Buffer,99,FilePtr);
  if(Buffer[0] != 'P' || Buffer[1] != '6')
     { fprintf(stderr, "Not a binary ppm file: %s\n", PPMfileName); exit(1); }
  if(Buffer[2] == 'A')
     NumComponents = 4;
  else
     NumComponents = 3;

  Buffer[0] = getc(FilePtr);
  while(Buffer[0] == '#' || Buffer[0] == '\n')
  {
     ungetc(Buffer[0], FilePtr);
     fgets(Buffer,99,FilePtr);
     Buffer[0] = getc(FilePtr);
  }

  ungetc(Buffer[0], FilePtr);

  fscanf(FilePtr, "%d %d %d\n", &Width, &Height, &Color);
  if(Color != 255)
     { fprintf(stderr, "File does not have True color?\n"); exit(1); }
  printf("Reading %dx%d image (%d Component) from [%s]. . .\n",
          Width, Height, NumComponents, PPMfileName);

  int LineWidth = Width*NumComponents;

  GLubyte* fBuffer = new GLubyte[Height*LineWidth];

  FBuffer = fBuffer;
  fBuffer += (Height*LineWidth - LineWidth); // Help the compiler optimize

  for(int i=Height; i>0; i--)
  { // Have to read in reverse for OpenGL windows.
    fread(fBuffer,LineWidth,1,FilePtr); // Let File buffer manage disk access
    fBuffer -= LineWidth;
  }
  fclose(FilePtr);

  return;
}

void Quit()
{
  delete[] FBuffer;
  exit(1);
}

void KeyBoardHandler(unsigned char key, int x, int y)
{
   if(key == 'q' || key == 'Q')
      Quit();
}

void Reshape(int w, int h)
{
  
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D(0, w, h, 0);
  
  glPixelZoom((GLfloat)w/Width, (GLfloat)h/Height);

  glClear(GL_COLOR_BUFFER_BIT);
}

void display4() // For some special ppm files
{

  glPixelStorei(GL_UNPACK_ALIGNMENT, 1); // Just to make sure
  glRasterPos2i(0,glutGet(GLUT_WINDOW_HEIGHT)); // Just to be sure

  glClear(GL_COLOR_BUFFER_BIT);
  glDrawPixels(Width,Height, GL_RGBA, GL_UNSIGNED_BYTE, FBuffer);
}

void display()
{
// printf("My images will seem reflected in screen Y dimension.\n \
//         To fix this you will need to draw one pixel at a time \n \
//         from the end of the file (i.e., FBuffer in the source code)\n");

  glPixelStorei(GL_UNPACK_ALIGNMENT, 1); // Just to be sure
  glRasterPos2i(0,glutGet(GLUT_WINDOW_HEIGHT)); // Just to be sure

  glClear(GL_COLOR_BUFFER_BIT);
  glDrawPixels(Width,Height, GL_RGB, GL_UNSIGNED_BYTE, FBuffer);
}

void Init(int argc, char *argv[])
{

   if(argc < 2) {printf("No ppm File Specified\n"); exit(1);}
   
   ReadPPM(argv[1]);

   glutInit(&argc, argv);
   glutInitWindowSize(Width, Height);
   glutCreateWindow("457 PPM Viewer");
   glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
   glutDisplayFunc(display);
   glutKeyboardFunc(KeyBoardHandler);
   glutReshapeFunc(Reshape);
}

main(int argc, char *argv[])
{
   Init(argc, argv);

   glutMainLoop();
}