exshade.c from Allegro game programming library at Krugle

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/*
 *    Example program for the Allegro library, by Patrick Hogan
 *
 *    This program demonstrates how to draw gouraud shaded (lit) sprites.
 */


#include <math.h>

#include "allegro.h"



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

AL_COLOR_MAP light_table;



int distance(int x1, int y1, int x2, int y2)
{
   int dx = x2 - x1;
   int dy = y2 - y1;
   int temp = sqrt((dx * dx) + (dy * dy));

   temp *= 2;
   if (temp > 255)
      temp = 255;

   return (255 - temp);
}



int main(int argc, char *argv[])
{
   AL_PALETTE pal;
   AL_BITMAP *buffer;
   AL_BITMAP *planet;
   char buf[256];

   allegro_init();
   al_install_keyboard();
   al_install_mouse();
   if (al_set_gfx_mode(AL_GFX_SAFE, 320, 240, 0, 0) != 0) {
      al_set_gfx_mode(AL_GFX_NONE, 0, 0, 0, 0);
      al_show_message("Unable to set any graphic mode\n%s\n", al_error);
      return 1;
   }
   al_text_mode(-1);

   al_replace_filename(buf, argv[0], "planet.pcx", sizeof(buf));

   planet = al_load_bitmap(buf, pal);
   if (!planet) {
      al_set_gfx_mode(AL_GFX_NONE, 0, 0, 0, 0);
      al_show_message("Error reading %s\n", buf);
      return 1;
   }

   buffer = al_create_bitmap(AL_SCREEN_W, AL_SCREEN_H);
   al_clear_bitmap(buffer);

   al_set_palette(pal);

   al_create_rgb_table(&rgb_table, pal, NULL);
   al_rgb_map = &rgb_table;

   al_create_light_table(&light_table, pal, 0, 0, 0, NULL);
   al_color_map = &light_table;

   al_set_trans_blender(0, 0, 0, 128);

   do {
      al_poll_mouse();

      al_draw_gouraud_sprite(buffer, planet, AL_SCREEN_W/2, AL_SCREEN_H/2,
			  distance(AL_SCREEN_W/2, AL_SCREEN_H/2, al_mouse_x, al_mouse_y),
			  distance(AL_SCREEN_W/2 + planet->w, AL_SCREEN_H/2, al_mouse_x, al_mouse_y),
			  distance(AL_SCREEN_W/2 + planet->w, AL_SCREEN_H/2 + planet->h, al_mouse_x, al_mouse_y),
			  distance(AL_SCREEN_W/2, AL_SCREEN_H/2 + planet->h, al_mouse_x, al_mouse_y));

      al_put_text(buffer, al_font_8x8, "Gouraud Shaded Sprite Demo", 0, 0, al_palette_color[10]);

      al_show_mouse(buffer);
      al_blit(buffer, al_screen, 0, 0, 0, 0, AL_SCREEN_W, AL_SCREEN_H);
      al_show_mouse(NULL);

   } while (!al_key_pressed());

   al_destroy_bitmap(planet);
   al_destroy_bitmap(buffer);

   return 0;
}

AL_END_OF_MAIN();
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