/*  alpha_fade2.c  uses jpegread to input a .jpg file, needs jpeg.h  */
/*                also needs files p1.jpg, p2.jpg, p3.jpg. p4.jpg */
#include <GL/glut.h>
#include <stdio.h>

static int fade=0;
static GLubyte rgbpix1[4*480*400]; /* size bigger than p1.jpg */
static int width1 = 480;               /* also read in */
static int height1 = 400; 
static int alpha1 = 255;
static GLubyte rgbpix2[4*480*400]; /* size bigger than p2.jpg */
static int width2 = 480;               /* also read in */
static int height2 = 400; 
static int alpha2 = 0;
static GLubyte rgbpix3[4*480*400]; /* size bigger than p3.jpg */
static int width3 = 480;               /* also read in */
static int height3 = 400; 
static int alpha3 = 0;
static GLubyte rgbpix4[4*480*400]; /* size bigger than p4.jpg */
static int width4 = 480;               /* also read in */
static int height4 = 400; 
static int alpha4 = 0;


void display(void)
{
  char *p;
  char msg[] = "press f for alpha fade";
  
  /* clear window */
  glClear(GL_COLOR_BUFFER_BIT); 
  glLoadIdentity ();
  glColor3f(0.0, 0.0, 0.0);


  /* draw .jpg files */  
  glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
  glRasterPos2f(0.0, 0.1);
  glDrawPixels(width1, height1, GL_RGBA, GL_UNSIGNED_BYTE, rgbpix1);
  glRasterPos2f(0.0, 0.1);
  glDrawPixels(width2, height2, GL_RGBA, GL_UNSIGNED_BYTE, rgbpix2);
  glRasterPos2f(0.0, 0.1);
  glDrawPixels(width3, height3, GL_RGBA, GL_UNSIGNED_BYTE, rgbpix3);
  glRasterPos2f(0.0, 0.1);
  glDrawPixels(width4, height4, GL_RGBA, GL_UNSIGNED_BYTE, rgbpix4);
  
  
  /* draw text */
  glEnable(GL_LINE_SMOOTH);
  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
  glEnable(GL_BLEND);
  glLoadIdentity ();
  glTranslatef(0.02, 0.02, 0.0);
  glScalef(0.0005, 0.0005, 0.0);
  for(p=msg; *p; p++)
    glutStrokeCharacter(GLUT_STROKE_ROMAN, *p);
  glFlush();
  glutSwapBuffers();
}

void myreshape(int h, int w)
{
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D(0.0, 1.0, 0.0, 1.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  glViewport(0,0,h,w);
}

void init()
{
  int status;
  
  printf("jpegread on file p1.jpg\n");
  status = jpegread("p1.jpg", alpha1, &width1, &height1, rgbpix1);
  printf("jpegread returned status=%d, width1=%d, height1=%d, alpha1=%d \n",
         status, width1, height1, alpha1);
  printf("jpegread on file p2.jpg\n");
  status = jpegread("p2.jpg", alpha2, &width2, &height2, rgbpix2);
  printf("jpegread returned status=%d, width2=%d, height2=%d, alpha3=%d \n",
         status, width2, height2, alpha2);
  printf("jpegread on file p3.jpg\n");
  status = jpegread("p3.jpg", alpha3, &width3, &height3, rgbpix3);
  printf("jpegread returned status=%d, width3=%d, height3=%d, alpha3=%d \n",
         status, width3, height3, alpha3);
  printf("jpegread on file p4.jpg\n");
  status = jpegread("p4.jpg", alpha4, &width4, &height4, rgbpix4);
  printf("jpegread returned status=%d, width4=%d, height4=%d, alpha4=%d \n",
         status, width4, height4, alpha4);

  /* set clear color to white */
  glClearColor (1.0, 1.0, 1.0, 0.0);
  /* set fill  color to black */

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D(0.0, 1.0, 0.0, 1.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  glViewport(0,0,480,400);
}
static void key(unsigned char k, int x, int y)
{
  int i;
  
  switch (k) {
  case 'f':
    fade++;
    if(rgbpix2[3]<256-31)
      for(i=3; i<4*480*400; i+=4) rgbpix2[i]+=31;
    else if(rgbpix3[3]<256-63)
      for(i=3; i<4*480*400; i+=4) rgbpix3[i]+=63;
    else if(rgbpix4[3]<256-63)
      for(i=3; i<4*480*400; i+=4) rgbpix4[i]+=63;  
    else
      for(i=3; i<4*480*400; i+=4)
      {
        rgbpix2[i]=0;
        rgbpix3[i]=0;
        rgbpix4[i]=0;
      }
    break;
  case 'q':
    exit(0);
    break;
  default:
    break;
  }
  printf("alpha2=%d, alpha3=%d, alpha4=%d\n",
         rgbpix2[3], rgbpix3[3], rgbpix4[3]);
  glutPostRedisplay();
} /* end key function */

int main(int argc, char* argv[])
{
  glutInit(&argc,argv);
  glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);  
  glutInitWindowSize(480,400);
  glutInitWindowPosition(100,100); 
  
  glutCreateWindow(argv[0]);
  glutReshapeFunc(myreshape);
  glutKeyboardFunc(key);
  glutDisplayFunc(display);
  init();
  glutMainLoop();
  return 0;
}