/*
 *    Example program for the Allegro library, by Grzegorz Adam Hankiewicz.
 *
 *    This program demonstrates how to create custom graphic effects
 *    with the create_color_table function. Allegro drawing routines
 *    are affected by any color table you might have set up. In
 *    the first part of this example, a greyscale color table is
 *    set. The result is that a simple rectfill call, instead of
 *    drawing a rectangle with color zero, uses the already drawn
 *    pixels to determine the pixel to be drawn (read the comment
 *    of return_grey_color() for a precise description of the
 *    algorithm). In the second part of the test, the color table
 *    is changed to be an inverse table, meaning that any pixel
 *    drawn will be shown as its color values had been inverted.
 */


#include <allegro.h>



/* RGB -> color mapping table. Not needed, but speeds things up */
RGB_MAP rgb_table;

/* greyscale & negative color mapping table */
COLOR_MAP greyscale_table, negative_table;

PALETTE pal;
BITMAP *background;
BITMAP *temp;



/* Here comes our custom function. It's designed to take the input colors
 * (red, green & blue) and return a greyscale color for it. This way, when
 * any drawing function draws say over green, it draws the greyscale color
 * for green.
 * 'pal' is the palette we are looking in to find the colors.
 * Now, imagine we want to draw a pixel with color A, over color B.
 * Once the table is created, set, and the drawing mode is TRANSLUCENT, then
 * A is the 'x' color passed to the function and B is the 'y' color passed
 * to the function.
 * Since we want a greyscale effect with no matter what A (or 'x') color, we
 * ignore it and use y to look at the palette.
 * NOTE:
 * When you return the rgb value, you don't need to search the palette for
 * the nearest color, Allegro does this automatically.
 */

void return_grey_color(AL_CONST PALETTE pal, int x, int y, RGB *rgb)
{
   int c;

   /* first create the greyscale color */
   c = (pal[y].r*0.3 + pal[y].g*0.5 + pal[y].b*0.2);

   /* now assign to our rgb triplet the palette greyscale color... */
   rgb->r = rgb->g = rgb->b = c;
}



/* The negative_color function is quite the same like the grayscale one,
 * since we are ignoring the value of the drawn color (aka x).
 */

void return_negative_color(AL_CONST PALETTE pal, int x, int y, RGB *rgb)
{
   /* To get the negative color, subtract the color values of red, green
    * and blue from the full (63) color value.
    */
   rgb->r = 63-pal[y].r;
   rgb->g = 63-pal[y].g;
   rgb->b = 63-pal[y].b;
}



void generate_background(void)
{
   int i;

   /* First get some usual colors. */
   generate_332_palette(pal);

   /* Now remap the first 64 for a perfect greyscale gradient. */
   for (i=0; i<64; i++) {
      pal[i].r = i;
      pal[i].g = i;
      pal[i].b = i;
   }

   /* Draws some things on the screen using not-greyscale colors. */
   for (i=0; i<3000; i++)
      circlefill(background, AL_RAND() % 320, AL_RAND() % 200,
		 AL_RAND() % 25, 64 + AL_RAND() % 192);
}



int main(void)
{
   int x, y, deltax=1, deltay=1;

   if (allegro_init() != 0)
      return 1;
   install_keyboard();

   temp = create_bitmap(320, 200);
   background = create_bitmap(320, 200);

   generate_background();

   /* This isn't needed, but it speeds up the color table calculations. */
   create_rgb_table(&rgb_table, pal, NULL);
   rgb_map = &rgb_table;

   /* Build a color lookup table for greyscale effect. */
   create_color_table(&greyscale_table, pal, return_grey_color, NULL);

   /* Build a color lookup table for negative effect. */
   create_color_table(&negative_table, pal, return_negative_color, NULL);

   if (set_gfx_mode(GFX_AUTODETECT, 320, 200, 0, 0) != 0) {
      if (set_gfx_mode(GFX_SAFE, 320, 200, 0, 0) != 0) {
	 set_gfx_mode(GFX_TEXT, 0, 0, 0, 0);
	 allegro_message("Unable to set any graphic mode\n%s\n",
			 allegro_error);
	 return 1;
      }
   }

   set_palette(pal);

   /* We have set the drawing mode to TRANS. This makes all the drawing
    * functions use the general color_map table, which is _NOT_ translucent,
    * since we are using a custom color_map table.
    */
   drawing_mode(DRAW_MODE_TRANS, NULL, 0, 0);

   /* select the greyscale table */
   color_map = &greyscale_table;

   x = y = 50;
   blit(background, temp, 0, 0, 0, 0, 320, 200);
   rectfill(temp, x, y, x+50, y+50, 0);

   blit(temp, screen, 0, 0, 0, 0, 320, 200);

   while (!keypressed()) {
      x += deltax;
      y += deltay;

      if ((x < 1) || (x > 320-50))
	 deltax *= -1;

      if ((y < 1) || (y > 200-50))
	 deltay *= -1;

      blit(background, temp, 0, 0, 0, 0, 320, 200);
      textout_centre_ex(temp, font, "Greyscale effect",
			SCREEN_W/2, SCREEN_H/2, makecol(0, 0, 255), -1);
      rectfill(temp, x, y, x+50, y+50, 0);
      vsync();
      blit(temp, screen, 0, 0, 0, 0, 320, 200);

      /* slow down the animation for modern machines */
      rest(1);
   }

   clear_keybuf();

   /* Now it's time for the negative part. The negative example is easier to
    * see with greyscale colors. Therefore we will change the color of the
    * background to a greyscale one, but only in a restricted area...
    */

   rectfill(background, SCREEN_H/4, SCREEN_H/4,
	    background->w-SCREEN_H/4, background->h-SCREEN_H/4, 0);

   /* this should go inside the next loop, but since we won't use the
    * background image any more, we can optimize it's speed printing the
    * text now.
    */
   textout_centre_ex(background, font, "Negative effect",
		     SCREEN_W/2, SCREEN_H/2, makecol(0, 0, 0), -1);

   /* switch the active color table... */
   color_map = &negative_table;

   blit(background, temp, 0, 0, 0, 0, 320, 200);
   rectfill(temp, x, y, x+50, y+50, 0);

   blit(temp, screen, 0, 0, 0, 0, 320, 200);

   while (!keypressed()) {
      x += deltax;
      y += deltay;

      if ((x < 1) || (x > 320-50))
	 deltax *= -1;

      if ((y < 1) || (y > 200-50))
	 deltay *= -1;

      blit(background, temp, 0, 0, 0, 0, 320, 200);
      rectfill(temp, x, y, x+50, y+50, 0);
      vsync();
      blit(temp, screen, 0, 0, 0, 0, 320, 200);

      /* slow down the animation for modern machines */
      rest(1);
   }

   destroy_bitmap(background);
   destroy_bitmap(temp);

   return 0;
}

END_OF_MAIN()