test/testalpha.c - third_party/sdl - Git at Google


 /* Simple program:  Fill a colormap with gray and stripe it down the screen,
 		    Then move an alpha valued sprite around the screen.
  */

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <math.h>

 #include "SDL.h"

 #define FRAME_TICKS	(1000/30)       /* 30 frames/second */

 /* Call this instead of exit(), so we can clean up SDL: atexit() is evil. */
 static void
 quit(int rc)
 {
     SDL_Quit();
     exit(rc);
 }

 /* Fill the screen with a gradient */
 static void
 FillBackground(SDL_Surface * screen)
 {
     Uint8 *buffer;
     Uint16 *buffer16;
     Uint16 color;
     Uint8 gradient;
     int i, k;

     /* Set the surface pixels and refresh! */
     if (SDL_LockSurface(screen) < 0) {
         fprintf(stderr, "Couldn't lock the display surface: %s\n",
                 SDL_GetError());
         quit(2);
     }
     buffer = (Uint8 *) screen->pixels;
     if (screen->format->BytesPerPixel != 2) {
         for (i = 0; i < screen->h; ++i) {
             memset(buffer, (i * 255) / screen->h,
                    screen->w * screen->format->BytesPerPixel);
             buffer += screen->pitch;
         }
     } else {
         for (i = 0; i < screen->h; ++i) {
             gradient = ((i * 255) / screen->h);
             color =
                 (Uint16) SDL_MapRGB(screen->format, gradient, gradient,
                                     gradient);
             buffer16 = (Uint16 *) buffer;
             for (k = 0; k < screen->w; k++) {
                 *(buffer16 + k) = color;
             }
             buffer += screen->pitch;
         }
     }

     SDL_UnlockSurface(screen);
     SDL_UpdateRect(screen, 0, 0, 0, 0);
 }

 /* Create a "light" -- a yellowish surface with variable alpha */
 SDL_Surface *
 CreateLight(int radius)
 {
     Uint8 trans, alphamask;
     int range, addition;
     int xdist, ydist;
     Uint16 x, y;
     Uint16 skip;
     Uint32 pixel;
     SDL_Surface *light;

 #ifdef LIGHT_16BIT
     Uint16 *buf;

     /* Create a 16 (4/4/4/4) bpp square with a full 4-bit alpha channel */
     /* Note: this isn't any faster than a 32 bit alpha surface */
     alphamask = 0x0000000F;
     light = SDL_CreateRGBSurface(SDL_SWSURFACE, 2 * radius, 2 * radius, 16,
                                  0x0000F000, 0x00000F00, 0x000000F0,
                                  alphamask);
 #else
     Uint32 *buf;

     /* Create a 32 (8/8/8/8) bpp square with a full 8-bit alpha channel */
     alphamask = 0x000000FF;
     light = SDL_CreateRGBSurface(SDL_SWSURFACE, 2 * radius, 2 * radius, 32,
                                  0xFF000000, 0x00FF0000, 0x0000FF00,
                                  alphamask);
     if (light == NULL) {
         fprintf(stderr, "Couldn't create light: %s\n", SDL_GetError());
         return (NULL);
     }
 #endif

     /* Fill with a light yellow-orange color */
     skip = light->pitch - (light->w * light->format->BytesPerPixel);
 #ifdef LIGHT_16BIT
     buf = (Uint16 *) light->pixels;
 #else
     buf = (Uint32 *) light->pixels;
 #endif
     /* Get a tranparent pixel value - we'll add alpha later */
     pixel = SDL_MapRGBA(light->format, 0xFF, 0xDD, 0x88, 0);
     for (y = 0; y < light->h; ++y) {
         for (x = 0; x < light->w; ++x) {
             *buf++ = pixel;
         }
         buf += skip;            /* Almost always 0, but just in case... */
     }

     /* Calculate alpha values for the surface. */
 #ifdef LIGHT_16BIT
     buf = (Uint16 *) light->pixels;
 #else
     buf = (Uint32 *) light->pixels;
 #endif
     for (y = 0; y < light->h; ++y) {
         for (x = 0; x < light->w; ++x) {
             /* Slow distance formula (from center of light) */
             xdist = x - (light->w / 2);
             ydist = y - (light->h / 2);
             range = (int) sqrt(xdist * xdist + ydist * ydist);

             /* Scale distance to range of transparency (0-255) */
             if (range > radius) {
                 trans = alphamask;
             } else {
                 /* Increasing transparency with distance */
                 trans = (Uint8) ((range * alphamask) / radius);

                 /* Lights are very transparent */
                 addition = (alphamask + 1) / 8;
                 if ((int) trans + addition > alphamask) {
                     trans = alphamask;
                 } else {
                     trans += addition;
                 }
             }
             /* We set the alpha component as the right N bits */
             *buf++ |= (255 - trans);
         }
         buf += skip;            /* Almost always 0, but just in case... */
     }
     /* Enable RLE acceleration of this alpha surface */
     SDL_SetAlpha(light, SDL_SRCALPHA | SDL_RLEACCEL, 0);

     /* We're done! */
     return (light);
 }

 static Uint32 flashes = 0;
 static Uint32 flashtime = 0;

 void
 FlashLight(SDL_Surface * screen, SDL_Surface * light, int x, int y)
 {
     SDL_Rect position;
     Uint32 ticks1;
     Uint32 ticks2;

     /* Easy, center light */
     position.x = x - (light->w / 2);
     position.y = y - (light->h / 2);
     position.w = light->w;
     position.h = light->h;
     ticks1 = SDL_GetTicks();
     SDL_BlitSurface(light, NULL, screen, &position);
     ticks2 = SDL_GetTicks();
     SDL_UpdateRects(screen, 1, &position);
     ++flashes;

     /* Update time spend doing alpha blitting */
     flashtime += (ticks2 - ticks1);
 }

 static int sprite_visible = 0;
 static SDL_Surface *sprite;
 static SDL_Surface *backing;
 static SDL_Rect position;
 static int x_vel, y_vel;
 static int alpha_vel;

 int
 LoadSprite(SDL_Surface * screen, char *file)
 {
     SDL_Surface *converted;

     /* Load the sprite image */
     sprite = SDL_LoadBMP(file);
     if (sprite == NULL) {
         fprintf(stderr, "Couldn't load %s: %s", file, SDL_GetError());
         return (-1);
     }

     /* Set transparent pixel as the pixel at (0,0) */
     if (sprite->format->palette) {
         SDL_SetColorKey(sprite, SDL_SRCCOLORKEY, *(Uint8 *) sprite->pixels);
     }

     /* Convert sprite to video format */
     converted = SDL_DisplayFormat(sprite);
     SDL_FreeSurface(sprite);
     if (converted == NULL) {
         fprintf(stderr, "Couldn't convert background: %s\n", SDL_GetError());
         return (-1);
     }
     sprite = converted;

     /* Create the background */
     backing = SDL_CreateRGBSurface(SDL_SWSURFACE, sprite->w, sprite->h, 8,
                                    0, 0, 0, 0);
     if (backing == NULL) {
         fprintf(stderr, "Couldn't create background: %s\n", SDL_GetError());
         SDL_FreeSurface(sprite);
         return (-1);
     }

     /* Convert background to video format */
     converted = SDL_DisplayFormat(backing);
     SDL_FreeSurface(backing);
     if (converted == NULL) {
         fprintf(stderr, "Couldn't convert background: %s\n", SDL_GetError());
         SDL_FreeSurface(sprite);
         return (-1);
     }
     backing = converted;

     /* Set the initial position of the sprite */
     position.x = (screen->w - sprite->w) / 2;
     position.y = (screen->h - sprite->h) / 2;
     position.w = sprite->w;
     position.h = sprite->h;
     x_vel = 0;
     y_vel = 0;
     alpha_vel = 1;

     /* We're ready to roll. :) */
     return (0);
 }

 void
 AttractSprite(Uint16 x, Uint16 y)
 {
     x_vel = ((int) x - position.x) / 10;
     y_vel = ((int) y - position.y) / 10;
 }

 void
 MoveSprite(SDL_Surface * screen, SDL_Surface * light)
 {
     SDL_Rect updates[2];
     int alpha;

     /* Erase the sprite if it was visible */
     if (sprite_visible) {
         updates[0] = position;
         SDL_BlitSurface(backing, NULL, screen, &updates[0]);
     } else {
         updates[0].x = 0;
         updates[0].y = 0;
         updates[0].w = 0;
         updates[0].h = 0;
         sprite_visible = 1;
     }

     /* Since the sprite is off the screen, we can do other drawing
        without being overwritten by the saved area behind the sprite.
      */
     if (light != NULL) {
         int x, y;

         SDL_GetMouseState(&x, &y);
         FlashLight(screen, light, x, y);
     }

     /* Move the sprite, bounce at the wall */
     position.x += x_vel;
     if ((position.x < 0) || (position.x >= screen->w)) {
         x_vel = -x_vel;
         position.x += x_vel;
     }
     position.y += y_vel;
     if ((position.y < 0) || (position.y >= screen->h)) {
         y_vel = -y_vel;
         position.y += y_vel;
     }

     /* Update transparency (fade in and out) */
     alpha = sprite->format->alpha;
     if ((alpha + alpha_vel) < 0) {
         alpha_vel = -alpha_vel;
     } else if ((alpha + alpha_vel) > 255) {
         alpha_vel = -alpha_vel;
     }
     SDL_SetAlpha(sprite, SDL_SRCALPHA, (Uint8) (alpha + alpha_vel));

     /* Save the area behind the sprite */
     updates[1] = position;
     SDL_BlitSurface(screen, &updates[1], backing, NULL);

     /* Blit the sprite onto the screen */
     updates[1] = position;
     SDL_BlitSurface(sprite, NULL, screen, &updates[1]);

     /* Make it so! */
     SDL_UpdateRects(screen, 2, updates);
 }

 void
 WarpSprite(SDL_Surface * screen, int x, int y)
 {
     SDL_Rect updates[2];

     /* Erase, move, Draw, update */
     updates[0] = position;
     SDL_BlitSurface(backing, NULL, screen, &updates[0]);
     position.x = x - sprite->w / 2;     /* Center about X */
     position.y = y - sprite->h / 2;     /* Center about Y */
     updates[1] = position;
     SDL_BlitSurface(screen, &updates[1], backing, NULL);
     updates[1] = position;
     SDL_BlitSurface(sprite, NULL, screen, &updates[1]);
     SDL_UpdateRects(screen, 2, updates);
 }

 int
 main(int argc, char *argv[])
 {
     const SDL_VideoInfo *info;
     SDL_Surface *screen;
     int w, h;
     Uint8 video_bpp;
     Uint32 videoflags;
     int i, done;
     SDL_Event event;
     SDL_Surface *light;
     int mouse_pressed;
     Uint32 ticks, lastticks;


     /* Initialize SDL */
     if (SDL_Init(SDL_INIT_VIDEO) < 0) {
         fprintf(stderr, "Couldn't initialize SDL: %s\n", SDL_GetError());
         return (1);
     }

     /* Alpha blending doesn't work well at 8-bit color */
 #ifdef _WIN32_WCE
     /* Pocket PC */
     w = 240;
     h = 320;
 #else
     w = 640;
     h = 480;
 #endif
     info = SDL_GetVideoInfo();
     if (info->vfmt->BitsPerPixel > 8) {
         video_bpp = info->vfmt->BitsPerPixel;
     } else {
         video_bpp = 16;
         fprintf(stderr, "forced 16 bpp mode\n");
     }
     videoflags = SDL_SWSURFACE;
     for (i = 1; argv[i]; ++i) {
         if (strcmp(argv[i], "-bpp") == 0) {
             video_bpp = atoi(argv[++i]);
             if (video_bpp <= 8) {
                 video_bpp = 16;
                 fprintf(stderr, "forced 16 bpp mode\n");
             }
         } else if (strcmp(argv[i], "-hw") == 0) {
             videoflags |= SDL_HWSURFACE;
         } else if (strcmp(argv[i], "-warp") == 0) {
             videoflags |= SDL_HWPALETTE;
         } else if (strcmp(argv[i], "-width") == 0 && argv[i + 1]) {
             w = atoi(argv[++i]);
         } else if (strcmp(argv[i], "-height") == 0 && argv[i + 1]) {
             h = atoi(argv[++i]);
         } else if (strcmp(argv[i], "-resize") == 0) {
             videoflags |= SDL_RESIZABLE;
         } else if (strcmp(argv[i], "-noframe") == 0) {
             videoflags |= SDL_NOFRAME;
         } else if (strcmp(argv[i], "-fullscreen") == 0) {
             videoflags |= SDL_FULLSCREEN;
         } else {
             fprintf(stderr,
                     "Usage: %s [-width N] [-height N] [-bpp N] [-warp] [-hw] [-fullscreen]\n",
                     argv[0]);
             quit(1);
         }
     }

     /* Set video mode */
     if ((screen = SDL_SetVideoMode(w, h, video_bpp, videoflags)) == NULL) {
         fprintf(stderr, "Couldn't set %dx%dx%d video mode: %s\n",
                 w, h, video_bpp, SDL_GetError());
         quit(2);
     }
     FillBackground(screen);

     /* Create the light */
     light = CreateLight(82);
     if (light == NULL) {
         quit(1);
     }

     /* Load the sprite */
     if (LoadSprite(screen, "icon.bmp") < 0) {
         SDL_FreeSurface(light);
         quit(1);
     }

     /* Print out information about our surfaces */
     printf("Screen is at %d bits per pixel\n", screen->format->BitsPerPixel);
     if ((screen->flags & SDL_HWSURFACE) == SDL_HWSURFACE) {
         printf("Screen is in video memory\n");
     } else {
         printf("Screen is in system memory\n");
     }
     if ((screen->flags & SDL_DOUBLEBUF) == SDL_DOUBLEBUF) {
         printf("Screen has double-buffering enabled\n");
     }
     if ((sprite->flags & SDL_HWSURFACE) == SDL_HWSURFACE) {
         printf("Sprite is in video memory\n");
     } else {
         printf("Sprite is in system memory\n");
     }

     /* Run a sample blit to trigger blit acceleration */
     MoveSprite(screen, NULL);
     if ((sprite->flags & SDL_HWACCEL) == SDL_HWACCEL) {
         printf("Sprite blit uses hardware alpha acceleration\n");
     } else {
         printf("Sprite blit dosn't uses hardware alpha acceleration\n");
     }

     /* Set a clipping rectangle to clip the outside edge of the screen */
     {
         SDL_Rect clip;
         clip.x = 32;
         clip.y = 32;
         clip.w = screen->w - (2 * 32);
         clip.h = screen->h - (2 * 32);
         SDL_SetClipRect(screen, &clip);
     }

     /* Wait for a keystroke */
     lastticks = SDL_GetTicks();
     done = 0;
     mouse_pressed = 0;
     while (!done) {
         /* Update the frame -- move the sprite */
         if (mouse_pressed) {
             MoveSprite(screen, light);
             mouse_pressed = 0;
         } else {
             MoveSprite(screen, NULL);
         }

         /* Slow down the loop to 30 frames/second */
         ticks = SDL_GetTicks();
         if ((ticks - lastticks) < FRAME_TICKS) {
 #ifdef CHECK_SLEEP_GRANULARITY
             fprintf(stderr, "Sleeping %d ticks\n",
                     FRAME_TICKS - (ticks - lastticks));
 #endif
             SDL_Delay(FRAME_TICKS - (ticks - lastticks));
 #ifdef CHECK_SLEEP_GRANULARITY
             fprintf(stderr, "Slept %d ticks\n", (SDL_GetTicks() - ticks));
 #endif
         }
         lastticks = ticks;

         /* Check for events */
         while (SDL_PollEvent(&event)) {
             switch (event.type) {
             case SDL_VIDEORESIZE:
                 screen =
                     SDL_SetVideoMode(event.resize.w, event.resize.h,
                                      video_bpp, videoflags);
                 if (screen) {
                     FillBackground(screen);
                 }
                 break;
                 /* Attract sprite while mouse is held down */
             case SDL_MOUSEMOTION:
                 if (event.motion.state != 0) {
                     AttractSprite(event.motion.x, event.motion.y);
                     mouse_pressed = 1;
                 }
                 break;
             case SDL_MOUSEBUTTONDOWN:
                 if (event.button.button == 1) {
                     AttractSprite(event.button.x, event.button.y);
                     mouse_pressed = 1;
                 } else {
                     SDL_Rect area;

                     area.x = event.button.x - 16;
                     area.y = event.button.y - 16;
                     area.w = 32;
                     area.h = 32;
                     SDL_FillRect(screen, &area, 0);
                     SDL_UpdateRects(screen, 1, &area);
                 }
                 break;
             case SDL_KEYDOWN:
                 if (event.key.keysym.sym == SDLK_ESCAPE) {
                     done = 1;
                 }
                 break;
             case SDL_QUIT:
                 done = 1;
                 break;
             default:
                 break;
             }
         }
     }
     SDL_FreeSurface(light);
     SDL_FreeSurface(sprite);
     SDL_FreeSurface(backing);

     /* Print out some timing information */
     if (flashes > 0) {
         printf("%d alpha blits, ~%4.4f ms per blit\n",
                flashes, (float) flashtime / flashes);
     }

     SDL_Quit();
     return (0);
 }

	/* Simple program: Fill a colormap with gray and stripe it down the screen,
	Then move an alpha valued sprite around the screen.
	*/

	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <math.h>

	#include "SDL.h"

	#define FRAME_TICKS (1000/30) /* 30 frames/second */

	/* Call this instead of exit(), so we can clean up SDL: atexit() is evil. */
	static void
	quit(int rc)
	{
	SDL_Quit();
	exit(rc);
	}

	/* Fill the screen with a gradient */
	static void
	FillBackground(SDL_Surface * screen)
	{
	Uint8 *buffer;
	Uint16 *buffer16;
	Uint16 color;
	Uint8 gradient;
	int i, k;

	/* Set the surface pixels and refresh! */
	if (SDL_LockSurface(screen) < 0) {
	fprintf(stderr, "Couldn't lock the display surface: %s\n",
	SDL_GetError());
	quit(2);
	}
	buffer = (Uint8 *) screen->pixels;
	if (screen->format->BytesPerPixel != 2) {
	for (i = 0; i < screen->h; ++i) {
	memset(buffer, (i * 255) / screen->h,
	screen->w * screen->format->BytesPerPixel);
	buffer += screen->pitch;
	}
	} else {
	for (i = 0; i < screen->h; ++i) {
	gradient = ((i * 255) / screen->h);
	color =
	(Uint16) SDL_MapRGB(screen->format, gradient, gradient,
	gradient);
	buffer16 = (Uint16 *) buffer;
	for (k = 0; k < screen->w; k++) {
	*(buffer16 + k) = color;
	}
	buffer += screen->pitch;
	}
	}

	SDL_UnlockSurface(screen);
	SDL_UpdateRect(screen, 0, 0, 0, 0);
	}

	/* Create a "light" -- a yellowish surface with variable alpha */
	SDL_Surface *
	CreateLight(int radius)
	{
	Uint8 trans, alphamask;
	int range, addition;
	int xdist, ydist;
	Uint16 x, y;
	Uint16 skip;
	Uint32 pixel;
	SDL_Surface *light;

	#ifdef LIGHT_16BIT
	Uint16 *buf;

	/* Create a 16 (4/4/4/4) bpp square with a full 4-bit alpha channel */
	/* Note: this isn't any faster than a 32 bit alpha surface */
	alphamask = 0x0000000F;
	light = SDL_CreateRGBSurface(SDL_SWSURFACE, 2 * radius, 2 * radius, 16,
	0x0000F000, 0x00000F00, 0x000000F0,
	alphamask);
	#else
	Uint32 *buf;

	/* Create a 32 (8/8/8/8) bpp square with a full 8-bit alpha channel */
	alphamask = 0x000000FF;
	light = SDL_CreateRGBSurface(SDL_SWSURFACE, 2 * radius, 2 * radius, 32,
	0xFF000000, 0x00FF0000, 0x0000FF00,
	alphamask);
	if (light == NULL) {
	fprintf(stderr, "Couldn't create light: %s\n", SDL_GetError());
	return (NULL);
	}
	#endif

	/* Fill with a light yellow-orange color */
	skip = light->pitch - (light->w * light->format->BytesPerPixel);
	#ifdef LIGHT_16BIT
	buf = (Uint16 *) light->pixels;
	#else
	buf = (Uint32 *) light->pixels;
	#endif
	/* Get a tranparent pixel value - we'll add alpha later */
	pixel = SDL_MapRGBA(light->format, 0xFF, 0xDD, 0x88, 0);
	for (y = 0; y < light->h; ++y) {
	for (x = 0; x < light->w; ++x) {
	*buf++ = pixel;
	}
	buf += skip; /* Almost always 0, but just in case... */
	}

	/* Calculate alpha values for the surface. */
	#ifdef LIGHT_16BIT
	buf = (Uint16 *) light->pixels;
	#else
	buf = (Uint32 *) light->pixels;
	#endif
	for (y = 0; y < light->h; ++y) {
	for (x = 0; x < light->w; ++x) {
	/* Slow distance formula (from center of light) */
	xdist = x - (light->w / 2);
	ydist = y - (light->h / 2);
	range = (int) sqrt(xdist * xdist + ydist * ydist);

	/* Scale distance to range of transparency (0-255) */
	if (range > radius) {
	trans = alphamask;
	} else {
	/* Increasing transparency with distance */
	trans = (Uint8) ((range * alphamask) / radius);

	/* Lights are very transparent */
	addition = (alphamask + 1) / 8;
	if ((int) trans + addition > alphamask) {
	trans = alphamask;
	} else {
	trans += addition;
	}
	}
	/* We set the alpha component as the right N bits */
	*buf++ \|= (255 - trans);
	}
	buf += skip; /* Almost always 0, but just in case... */
	}
	/* Enable RLE acceleration of this alpha surface */
	SDL_SetAlpha(light, SDL_SRCALPHA \| SDL_RLEACCEL, 0);

	/* We're done! */
	return (light);
	}

	static Uint32 flashes = 0;
	static Uint32 flashtime = 0;

	void
	FlashLight(SDL_Surface * screen, SDL_Surface * light, int x, int y)
	{
	SDL_Rect position;
	Uint32 ticks1;
	Uint32 ticks2;

	/* Easy, center light */
	position.x = x - (light->w / 2);
	position.y = y - (light->h / 2);
	position.w = light->w;
	position.h = light->h;
	ticks1 = SDL_GetTicks();
	SDL_BlitSurface(light, NULL, screen, &position);
	ticks2 = SDL_GetTicks();
	SDL_UpdateRects(screen, 1, &position);
	++flashes;

	/* Update time spend doing alpha blitting */
	flashtime += (ticks2 - ticks1);
	}

	static int sprite_visible = 0;
	static SDL_Surface *sprite;
	static SDL_Surface *backing;
	static SDL_Rect position;
	static int x_vel, y_vel;
	static int alpha_vel;

	int
	LoadSprite(SDL_Surface * screen, char *file)
	{
	SDL_Surface *converted;

	/* Load the sprite image */
	sprite = SDL_LoadBMP(file);
	if (sprite == NULL) {
	fprintf(stderr, "Couldn't load %s: %s", file, SDL_GetError());
	return (-1);
	}

	/* Set transparent pixel as the pixel at (0,0) */
	if (sprite->format->palette) {
	SDL_SetColorKey(sprite, SDL_SRCCOLORKEY, (Uint8 ) sprite->pixels);
	}

	/* Convert sprite to video format */
	converted = SDL_DisplayFormat(sprite);
	SDL_FreeSurface(sprite);
	if (converted == NULL) {
	fprintf(stderr, "Couldn't convert background: %s\n", SDL_GetError());
	return (-1);
	}
	sprite = converted;

	/* Create the background */
	backing = SDL_CreateRGBSurface(SDL_SWSURFACE, sprite->w, sprite->h, 8,
	0, 0, 0, 0);
	if (backing == NULL) {
	fprintf(stderr, "Couldn't create background: %s\n", SDL_GetError());
	SDL_FreeSurface(sprite);
	return (-1);
	}

	/* Convert background to video format */
	converted = SDL_DisplayFormat(backing);
	SDL_FreeSurface(backing);
	if (converted == NULL) {
	fprintf(stderr, "Couldn't convert background: %s\n", SDL_GetError());
	SDL_FreeSurface(sprite);
	return (-1);
	}
	backing = converted;

	/* Set the initial position of the sprite */
	position.x = (screen->w - sprite->w) / 2;
	position.y = (screen->h - sprite->h) / 2;
	position.w = sprite->w;
	position.h = sprite->h;
	x_vel = 0;
	y_vel = 0;
	alpha_vel = 1;

	/* We're ready to roll. :) */
	return (0);
	}

	void
	AttractSprite(Uint16 x, Uint16 y)
	{
	x_vel = ((int) x - position.x) / 10;
	y_vel = ((int) y - position.y) / 10;
	}

	void
	MoveSprite(SDL_Surface * screen, SDL_Surface * light)
	{
	SDL_Rect updates[2];
	int alpha;

	/* Erase the sprite if it was visible */
	if (sprite_visible) {
	updates[0] = position;
	SDL_BlitSurface(backing, NULL, screen, &updates[0]);
	} else {
	updates[0].x = 0;
	updates[0].y = 0;
	updates[0].w = 0;
	updates[0].h = 0;
	sprite_visible = 1;
	}

	/* Since the sprite is off the screen, we can do other drawing
	without being overwritten by the saved area behind the sprite.
	*/
	if (light != NULL) {
	int x, y;

	SDL_GetMouseState(&x, &y);
	FlashLight(screen, light, x, y);
	}

	/* Move the sprite, bounce at the wall */
	position.x += x_vel;
	if ((position.x < 0) \|\| (position.x >= screen->w)) {
	x_vel = -x_vel;
	position.x += x_vel;
	}
	position.y += y_vel;
	if ((position.y < 0) \|\| (position.y >= screen->h)) {
	y_vel = -y_vel;
	position.y += y_vel;
	}

	/* Update transparency (fade in and out) */
	alpha = sprite->format->alpha;
	if ((alpha + alpha_vel) < 0) {
	alpha_vel = -alpha_vel;
	} else if ((alpha + alpha_vel) > 255) {
	alpha_vel = -alpha_vel;
	}
	SDL_SetAlpha(sprite, SDL_SRCALPHA, (Uint8) (alpha + alpha_vel));

	/* Save the area behind the sprite */
	updates[1] = position;
	SDL_BlitSurface(screen, &updates[1], backing, NULL);

	/* Blit the sprite onto the screen */
	updates[1] = position;
	SDL_BlitSurface(sprite, NULL, screen, &updates[1]);

	/* Make it so! */
	SDL_UpdateRects(screen, 2, updates);
	}

	void
	WarpSprite(SDL_Surface * screen, int x, int y)
	{
	SDL_Rect updates[2];

	/* Erase, move, Draw, update */
	updates[0] = position;
	SDL_BlitSurface(backing, NULL, screen, &updates[0]);
	position.x = x - sprite->w / 2; /* Center about X */
	position.y = y - sprite->h / 2; /* Center about Y */
	updates[1] = position;
	SDL_BlitSurface(screen, &updates[1], backing, NULL);
	updates[1] = position;
	SDL_BlitSurface(sprite, NULL, screen, &updates[1]);
	SDL_UpdateRects(screen, 2, updates);
	}

	int
	main(int argc, char *argv[])
	{
	const SDL_VideoInfo *info;
	SDL_Surface *screen;
	int w, h;
	Uint8 video_bpp;
	Uint32 videoflags;
	int i, done;
	SDL_Event event;
	SDL_Surface *light;
	int mouse_pressed;
	Uint32 ticks, lastticks;


	/* Initialize SDL */
	if (SDL_Init(SDL_INIT_VIDEO) < 0) {
	fprintf(stderr, "Couldn't initialize SDL: %s\n", SDL_GetError());
	return (1);
	}

	/* Alpha blending doesn't work well at 8-bit color */
	#ifdef _WIN32_WCE
	/* Pocket PC */
	w = 240;
	h = 320;
	#else
	w = 640;
	h = 480;
	#endif
	info = SDL_GetVideoInfo();
	if (info->vfmt->BitsPerPixel > 8) {
	video_bpp = info->vfmt->BitsPerPixel;
	} else {
	video_bpp = 16;
	fprintf(stderr, "forced 16 bpp mode\n");
	}
	videoflags = SDL_SWSURFACE;
	for (i = 1; argv[i]; ++i) {
	if (strcmp(argv[i], "-bpp") == 0) {
	video_bpp = atoi(argv[++i]);
	if (video_bpp <= 8) {
	video_bpp = 16;
	fprintf(stderr, "forced 16 bpp mode\n");
	}
	} else if (strcmp(argv[i], "-hw") == 0) {
	videoflags \|= SDL_HWSURFACE;
	} else if (strcmp(argv[i], "-warp") == 0) {
	videoflags \|= SDL_HWPALETTE;
	} else if (strcmp(argv[i], "-width") == 0 && argv[i + 1]) {
	w = atoi(argv[++i]);
	} else if (strcmp(argv[i], "-height") == 0 && argv[i + 1]) {
	h = atoi(argv[++i]);
	} else if (strcmp(argv[i], "-resize") == 0) {
	videoflags \|= SDL_RESIZABLE;
	} else if (strcmp(argv[i], "-noframe") == 0) {
	videoflags \|= SDL_NOFRAME;
	} else if (strcmp(argv[i], "-fullscreen") == 0) {
	videoflags \|= SDL_FULLSCREEN;
	} else {
	fprintf(stderr,
	"Usage: %s [-width N] [-height N] [-bpp N] [-warp] [-hw] [-fullscreen]\n",
	argv[0]);
	quit(1);
	}
	}

	/* Set video mode */
	if ((screen = SDL_SetVideoMode(w, h, video_bpp, videoflags)) == NULL) {
	fprintf(stderr, "Couldn't set %dx%dx%d video mode: %s\n",
	w, h, video_bpp, SDL_GetError());
	quit(2);
	}
	FillBackground(screen);

	/* Create the light */
	light = CreateLight(82);
	if (light == NULL) {
	quit(1);
	}

	/* Load the sprite */
	if (LoadSprite(screen, "icon.bmp") < 0) {
	SDL_FreeSurface(light);
	quit(1);
	}

	/* Print out information about our surfaces */
	printf("Screen is at %d bits per pixel\n", screen->format->BitsPerPixel);
	if ((screen->flags & SDL_HWSURFACE) == SDL_HWSURFACE) {
	printf("Screen is in video memory\n");
	} else {
	printf("Screen is in system memory\n");
	}
	if ((screen->flags & SDL_DOUBLEBUF) == SDL_DOUBLEBUF) {
	printf("Screen has double-buffering enabled\n");
	}
	if ((sprite->flags & SDL_HWSURFACE) == SDL_HWSURFACE) {
	printf("Sprite is in video memory\n");
	} else {
	printf("Sprite is in system memory\n");
	}

	/* Run a sample blit to trigger blit acceleration */
	MoveSprite(screen, NULL);
	if ((sprite->flags & SDL_HWACCEL) == SDL_HWACCEL) {
	printf("Sprite blit uses hardware alpha acceleration\n");
	} else {
	printf("Sprite blit dosn't uses hardware alpha acceleration\n");
	}

	/* Set a clipping rectangle to clip the outside edge of the screen */
	{
	SDL_Rect clip;
	clip.x = 32;
	clip.y = 32;
	clip.w = screen->w - (2 * 32);
	clip.h = screen->h - (2 * 32);
	SDL_SetClipRect(screen, &clip);
	}

	/* Wait for a keystroke */
	lastticks = SDL_GetTicks();
	done = 0;
	mouse_pressed = 0;
	while (!done) {
	/* Update the frame -- move the sprite */
	if (mouse_pressed) {
	MoveSprite(screen, light);
	mouse_pressed = 0;
	} else {
	MoveSprite(screen, NULL);
	}

	/* Slow down the loop to 30 frames/second */
	ticks = SDL_GetTicks();
	if ((ticks - lastticks) < FRAME_TICKS) {
	#ifdef CHECK_SLEEP_GRANULARITY
	fprintf(stderr, "Sleeping %d ticks\n",
	FRAME_TICKS - (ticks - lastticks));
	#endif
	SDL_Delay(FRAME_TICKS - (ticks - lastticks));
	#ifdef CHECK_SLEEP_GRANULARITY
	fprintf(stderr, "Slept %d ticks\n", (SDL_GetTicks() - ticks));
	#endif
	}
	lastticks = ticks;

	/* Check for events */
	while (SDL_PollEvent(&event)) {
	switch (event.type) {
	case SDL_VIDEORESIZE:
	screen =
	SDL_SetVideoMode(event.resize.w, event.resize.h,
	video_bpp, videoflags);
	if (screen) {
	FillBackground(screen);
	}
	break;
	/* Attract sprite while mouse is held down */
	case SDL_MOUSEMOTION:
	if (event.motion.state != 0) {
	AttractSprite(event.motion.x, event.motion.y);
	mouse_pressed = 1;
	}
	break;
	case SDL_MOUSEBUTTONDOWN:
	if (event.button.button == 1) {
	AttractSprite(event.button.x, event.button.y);
	mouse_pressed = 1;
	} else {
	SDL_Rect area;

	area.x = event.button.x - 16;
	area.y = event.button.y - 16;
	area.w = 32;
	area.h = 32;
	SDL_FillRect(screen, &area, 0);
	SDL_UpdateRects(screen, 1, &area);
	}
	break;
	case SDL_KEYDOWN:
	if (event.key.keysym.sym == SDLK_ESCAPE) {
	done = 1;
	}
	break;
	case SDL_QUIT:
	done = 1;
	break;
	default:
	break;
	}
	}
	}
	SDL_FreeSurface(light);
	SDL_FreeSurface(sprite);
	SDL_FreeSurface(backing);

	/* Print out some timing information */
	if (flashes > 0) {
	printf("%d alpha blits, ~%4.4f ms per blit\n",
	flashes, (float) flashtime / flashes);
	}

	SDL_Quit();
	return (0);
	}