distrib/sdl-1.2.15/test/testalpha.c - emulator-unstable-refactoring - 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:
 #ifdef _WIN32_WCE
 					// there is no ESC key at all
 					done = 1;
 #else
 					if ( event.key.keysym.sym == SDLK_ESCAPE ) {
 						done = 1;
 					} else if (event.key.keysym.sym == SDLK_t) {
 						videoflags ^= SDL_FULLSCREEN;
 						screen = SDL_SetVideoMode(w, h, video_bpp, videoflags);
 						if ( screen == NULL ) {
 							fprintf(stderr, "Couldn't toggle video mode: %s\n",
 									SDL_GetError());
 							quit(2);
 						}
 						FillBackground(screen);
 					}
 #endif

 					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,(i255)/screen->h, screen->wscreen->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, 2radius, 2radius, 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, 2radius, 2radius, 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(xdistxdist+ydistydist);

	/* 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:
	#ifdef _WIN32_WCE
	// there is no ESC key at all
	done = 1;
	#else
	if ( event.key.keysym.sym == SDLK_ESCAPE ) {
	done = 1;
	} else if (event.key.keysym.sym == SDLK_t) {
	videoflags ^= SDL_FULLSCREEN;
	screen = SDL_SetVideoMode(w, h, video_bpp, videoflags);
	if ( screen == NULL ) {
	fprintf(stderr, "Couldn't toggle video mode: %s\n",
	SDL_GetError());
	quit(2);
	}
	FillBackground(screen);
	}
	#endif

	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);
	}