test/testalpha.c

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FUNCTIONS

This source file includes following functions.
  1. CreateLight
  2. FlashLight
  3. LoadSprite
  4. AttractSprite
  5. MoveSprite
  6. WarpSprite
  7. main

   1 
   2 /* Simple program:  Fill a colormap with gray and stripe it down the screen,
   3                     Then move an alpha valued sprite around the screen.
   4  */
   5 
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <string.h>
   9 #include <math.h>
  10 
  11 #include "SDL.h"
  12 
  13 #define FRAME_TICKS     (1000/30)               /* 30 frames/second */
  14 
  15 /* Create a "light" -- a yellowish surface with variable alpha */
  16 SDL_Surface *CreateLight(SDL_Surface *screen, int radius)
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  17 {
  18         Uint8  trans, alphamask;
  19         int    range, addition;
  20         int    xdist, ydist;
  21         Uint16 x, y;
  22         Uint16 skip;
  23         Uint32 pixel;
  24         SDL_Surface *light;
  25 
  26 #ifdef LIGHT_16BIT
  27         Uint16 *buf;
  28 
  29         /* Create a 16 (4/4/4/4) bpp square with a full 4-bit alpha channel */
  30         /* Note: this isn't any faster than a 32 bit alpha surface */
  31         alphamask = 0x0000000F;
  32         light = SDL_CreateRGBSurface(SDL_SWSURFACE, 2*radius, 2*radius, 16,
  33                         0x0000F000, 0x00000F00, 0x000000F0, alphamask);
  34 #else
  35         Uint32 *buf;
  36 
  37         /* Create a 32 (8/8/8/8) bpp square with a full 8-bit alpha channel */
  38         alphamask = 0x000000FF;
  39         light = SDL_CreateRGBSurface(SDL_SWSURFACE, 2*radius, 2*radius, 32,
  40                         0xFF000000, 0x00FF0000, 0x0000FF00, alphamask);
  41         if ( light == NULL ) {
  42                 fprintf(stderr, "Couldn't create light: %s\n", SDL_GetError());
  43                 return(NULL);
  44         }
  45 #endif
  46 
  47         /* Fill with a light yellow-orange color */
  48         skip = light->pitch-(light->w*light->format->BytesPerPixel);
  49 #ifdef LIGHT_16BIT
  50         buf = (Uint16 *)light->pixels;
  51 #else
  52         buf = (Uint32 *)light->pixels;
  53 #endif
  54         /* Get a tranparent pixel value - we'll add alpha later */
  55         pixel = SDL_MapRGBA(light->format, 0xFF, 0xDD, 0x88, 0);
  56         for ( y=0; y<light->h; ++y ) {
  57                 for ( x=0; x<light->w; ++x ) {
  58                         *buf++ = pixel;
  59                 }
  60                 buf += skip;    /* Almost always 0, but just in case... */
  61         }
  62 
  63         /* Calculate alpha values for the surface. */
  64 #ifdef LIGHT_16BIT
  65         buf = (Uint16 *)light->pixels;
  66 #else
  67         buf = (Uint32 *)light->pixels;
  68 #endif
  69         for ( y=0; y<light->h; ++y ) {
  70                 for ( x=0; x<light->w; ++x ) {
  71                         /* Slow distance formula (from center of light) */
  72                         xdist = x-(light->w/2);
  73                         ydist = y-(light->h/2);
  74                         range = (int)sqrt(xdist*xdist+ydist*ydist);
  75 
  76                         /* Scale distance to range of transparency (0-255) */
  77                         if ( range > radius ) {
  78                                 trans = alphamask;
  79                         } else {
  80                                 /* Increasing transparency with distance */
  81                                 trans = (Uint8)((range*alphamask)/radius);
  82 
  83                                 /* Lights are very transparent */
  84                                 addition = (alphamask+1)/8;
  85                                 if ( (int)trans+addition > alphamask ) {
  86                                         trans = alphamask;
  87                                 } else {
  88                                         trans += addition;
  89                                 }
  90                         }
  91                         /* We set the alpha component as the right N bits */
  92                         *buf++ |= (255-trans);
  93                 }
  94                 buf += skip;    /* Almost always 0, but just in case... */
  95         }
  96         /* Enable RLE acceleration of this alpha surface */
  97         SDL_SetAlpha(light, SDL_SRCALPHA|SDL_RLEACCEL, 0);
  98 
  99         /* We're done! */
 100         return(light);
 101 }
 102 
 103 static Uint32 flashes = 0;
 104 static Uint32 flashtime = 0;
 105 
 106 void FlashLight(SDL_Surface *screen, SDL_Surface *light, int x, int y)
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 107 {
 108         SDL_Rect position;
 109         Uint32   ticks1;
 110         Uint32   ticks2;
 111 
 112         /* Easy, center light */
 113         position.x = x-(light->w/2);
 114         position.y = y-(light->h/2);
 115         position.w = light->w;
 116         position.h = light->h;
 117         ticks1 = SDL_GetTicks();
 118         SDL_BlitSurface(light, NULL, screen, &position);
 119         ticks2 = SDL_GetTicks();
 120         SDL_UpdateRects(screen, 1, &position);
 121         ++flashes;
 122 
 123         /* Update time spend doing alpha blitting */
 124         flashtime += (ticks2-ticks1);
 125 }
 126 
 127 static int sprite_visible = 0;
 128 static SDL_Surface *sprite;
 129 static SDL_Surface *backing;
 130 static SDL_Rect    position;
 131 static int         x_vel, y_vel;
 132 static int         alpha_vel;
 133 
 134 int LoadSprite(SDL_Surface *screen, char *file)
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 135 {
 136         SDL_Surface *converted;
 137 
 138         /* Load the sprite image */
 139         sprite = SDL_LoadBMP(file);
 140         if ( sprite == NULL ) {
 141                 fprintf(stderr, "Couldn't load %s: %s", file, SDL_GetError());
 142                 return(-1);
 143         }
 144 
 145         /* Set transparent pixel as the pixel at (0,0) */
 146         if ( sprite->format->palette ) {
 147                 SDL_SetColorKey(sprite, SDL_SRCCOLORKEY,
 148                                                 *(Uint8 *)sprite->pixels);
 149         }
 150 
 151         /* Convert sprite to video format */
 152         converted = SDL_DisplayFormat(sprite);
 153         SDL_FreeSurface(sprite);
 154         if ( converted == NULL ) {
 155                 fprintf(stderr, "Couldn't convert background: %s\n",
 156                                                         SDL_GetError());
 157                 return(-1);
 158         }
 159         sprite = converted;
 160 
 161         /* Create the background */
 162         backing = SDL_CreateRGBSurface(SDL_SWSURFACE, sprite->w, sprite->h, 8,
 163                                                                 0, 0, 0, 0);
 164         if ( backing == NULL ) {
 165                 fprintf(stderr, "Couldn't create background: %s\n",
 166                                                         SDL_GetError());
 167                 SDL_FreeSurface(sprite);
 168                 return(-1);
 169         }
 170 
 171         /* Convert background to video format */
 172         converted = SDL_DisplayFormat(backing);
 173         SDL_FreeSurface(backing);
 174         if ( converted == NULL ) {
 175                 fprintf(stderr, "Couldn't convert background: %s\n",
 176                                                         SDL_GetError());
 177                 SDL_FreeSurface(sprite);
 178                 return(-1);
 179         }
 180         backing = converted;
 181 
 182         /* Set the initial position of the sprite */
 183         position.x = (screen->w-sprite->w)/2;
 184         position.y = (screen->h-sprite->h)/2;
 185         position.w = sprite->w;
 186         position.h = sprite->h;
 187         x_vel = 0; y_vel = 0;
 188         alpha_vel = 1;
 189 
 190         /* We're ready to roll. :) */
 191         return(0);
 192 }
 193 
 194 void AttractSprite(Uint16 x, Uint16 y)
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 195 {
 196         x_vel = ((int)x-position.x)/10;
 197         y_vel = ((int)y-position.y)/10;
 198 }
 199 
 200 void MoveSprite(SDL_Surface *screen, SDL_Surface *light)
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 201 {
 202         SDL_Rect updates[2];
 203         int alpha;
 204 
 205         /* Erase the sprite if it was visible */
 206         if ( sprite_visible ) {
 207                 updates[0] = position;
 208                 SDL_BlitSurface(backing, NULL, screen, &updates[0]);
 209         } else {
 210                 updates[0].x = 0; updates[0].y = 0;
 211                 updates[0].w = 0; updates[0].h = 0;
 212                 sprite_visible = 1;
 213         }
 214 
 215         /* Since the sprite is off the screen, we can do other drawing
 216            without being overwritten by the saved area behind the sprite.
 217          */
 218         if ( light != NULL ) {
 219                 int x, y;
 220 
 221                 SDL_GetMouseState(&x, &y);
 222                 FlashLight(screen, light, x, y);
 223         }
 224            
 225         /* Move the sprite, bounce at the wall */
 226         position.x += x_vel;
 227         if ( (position.x < 0) || (position.x >= screen->w) ) {
 228                 x_vel = -x_vel;
 229                 position.x += x_vel;
 230         }
 231         position.y += y_vel;
 232         if ( (position.y < 0) || (position.y >= screen->h) ) {
 233                 y_vel = -y_vel;
 234                 position.y += y_vel;
 235         }
 236 
 237         /* Update transparency (fade in and out) */
 238         alpha = sprite->format->alpha;
 239         if ( (alpha+alpha_vel) < 0 ) {
 240                 alpha_vel = -alpha_vel;
 241         } else
 242         if ( (alpha+alpha_vel) > 255 ) {
 243                 alpha_vel = -alpha_vel;
 244         }
 245         SDL_SetAlpha(sprite, SDL_SRCALPHA, (Uint8)(alpha+alpha_vel));
 246 
 247         /* Save the area behind the sprite */
 248         updates[1] = position;
 249         SDL_BlitSurface(screen, &updates[1], backing, NULL);
 250         
 251         /* Blit the sprite onto the screen */
 252         updates[1] = position;
 253         SDL_BlitSurface(sprite, NULL, screen, &updates[1]);
 254 
 255         /* Make it so! */
 256         SDL_UpdateRects(screen, 2, updates);
 257 }
 258 
 259 void WarpSprite(SDL_Surface *screen, int x, int y)
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 260 {
 261         SDL_Rect updates[2];
 262 
 263         /* Erase, move, Draw, update */
 264         updates[0] = position;
 265         SDL_BlitSurface(backing, NULL, screen, &updates[0]);
 266         position.x = x-sprite->w/2;     /* Center about X */
 267         position.y = y-sprite->h/2;     /* Center about Y */
 268         updates[1] = position;
 269         SDL_BlitSurface(screen, &updates[1], backing, NULL);
 270         updates[1] = position;
 271         SDL_BlitSurface(sprite, NULL, screen, &updates[1]);
 272         SDL_UpdateRects(screen, 2, updates);
 273 }
 274 
 275 int main(int argc, char *argv[])
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 276 {
 277         const SDL_VideoInfo *info;
 278         SDL_Surface *screen;
 279         Uint8  video_bpp;
 280         Uint32 videoflags;
 281         Uint8 *buffer;
 282         int    i, done;
 283         SDL_Event event;
 284         SDL_Surface *light;
 285         int mouse_pressed;
 286         Uint32 ticks, lastticks;
 287 
 288         /* Initialize SDL */
 289         if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
 290                 fprintf(stderr, "Couldn't initialize SDL: %s\n",SDL_GetError());
 291                 exit(1);
 292         }
 293         atexit(SDL_Quit);
 294 
 295         /* Alpha blending doesn't work well at 8-bit color */
 296         info = SDL_GetVideoInfo();
 297         if ( info->vfmt->BitsPerPixel > 8 ) {
 298                 video_bpp = info->vfmt->BitsPerPixel;
 299         } else {
 300                 video_bpp = 16;
 301         }
 302         videoflags = SDL_SWSURFACE;
 303         while ( argc > 1 ) {
 304                 --argc;
 305                 if ( strcmp(argv[argc-1], "-bpp") == 0 ) {
 306                         video_bpp = atoi(argv[argc]);
 307                         --argc;
 308                 } else
 309                 if ( strcmp(argv[argc], "-hw") == 0 ) {
 310                         videoflags |= SDL_HWSURFACE;
 311                 } else
 312                 if ( strcmp(argv[argc], "-warp") == 0 ) {
 313                         videoflags |= SDL_HWPALETTE;
 314                 } else
 315                 if ( strcmp(argv[argc], "-fullscreen") == 0 ) {
 316                         videoflags |= SDL_FULLSCREEN;
 317                 } else {
 318                         fprintf(stderr, 
 319                         "Usage: %s [-bpp N] [-warp] [-hw] [-fullscreen]\n",
 320                                                                 argv[0]);
 321                         exit(1);
 322                 }
 323         }
 324 
 325         /* Set 640x480 video mode */
 326         if ( (screen=SDL_SetVideoMode(640,480,video_bpp,videoflags)) == NULL ) {
 327                 fprintf(stderr, "Couldn't set 640x480x%d video mode: %s\n",
 328                                                 video_bpp, SDL_GetError());
 329                 exit(2);
 330         }
 331 
 332         /* Set the surface pixels and refresh! */
 333         if ( SDL_LockSurface(screen) < 0 ) {
 334                 fprintf(stderr, "Couldn't lock the display surface: %s\n",
 335                                                         SDL_GetError());
 336                 exit(2);
 337         }
 338         buffer=(Uint8 *)screen->pixels;
 339         for ( i=0; i<screen->h; ++i ) {
 340                 memset(buffer,(i*255)/screen->h, screen->pitch);
 341                 buffer += screen->pitch;
 342         }
 343         SDL_UnlockSurface(screen);
 344         SDL_UpdateRect(screen, 0, 0, 0, 0);
 345 
 346         /* Create the light */
 347         light = CreateLight(screen, 82);
 348         if ( light == NULL ) {
 349                 exit(1);
 350         }
 351 
 352         /* Load the sprite */
 353         if ( LoadSprite(screen, "icon.bmp") < 0 ) {
 354                 SDL_FreeSurface(light);
 355                 exit(1);
 356         }
 357 
 358         /* Set a clipping rectangle to clip the outside edge of the screen */
 359         { SDL_Rect clip;
 360                 clip.x = 32;
 361                 clip.y = 32;
 362                 clip.w = screen->w-(2*32);
 363                 clip.h = screen->h-(2*32);
 364                 SDL_SetClipRect(screen, &clip);
 365         }
 366 
 367         /* Wait for a keystroke */
 368         lastticks = SDL_GetTicks();
 369         done = 0;
 370         mouse_pressed = 0;
 371         while ( !done ) {
 372                 /* Update the frame -- move the sprite */
 373                 if ( mouse_pressed ) {
 374                         MoveSprite(screen, light);
 375                         mouse_pressed = 0;
 376                 } else {
 377                         MoveSprite(screen, NULL);
 378                 }
 379 
 380                 /* Slow down the loop to 30 frames/second */
 381                 ticks = SDL_GetTicks();
 382                 if ( (ticks-lastticks) < FRAME_TICKS ) {
 383 #ifdef CHECK_SLEEP_GRANULARITY
 384 fprintf(stderr, "Sleeping %d ticks\n", FRAME_TICKS-(ticks-lastticks));
 385 #endif
 386                         SDL_Delay(FRAME_TICKS-(ticks-lastticks));
 387 #ifdef CHECK_SLEEP_GRANULARITY
 388 fprintf(stderr, "Slept %d ticks\n", (SDL_GetTicks()-ticks));
 389 #endif
 390                 }
 391                 lastticks = ticks;
 392 
 393                 /* Check for events */
 394                 while ( SDL_PollEvent(&event) ) {
 395                         switch (event.type) {
 396                                 /* Attract sprite while mouse is held down */
 397                                 case SDL_MOUSEMOTION:
 398                                         if (event.motion.state != 0) {
 399                                                 AttractSprite(event.motion.x,
 400                                                                 event.motion.y);
 401                                                 mouse_pressed = 1;
 402                                         }
 403                                         break;
 404                                 case SDL_MOUSEBUTTONDOWN:
 405                                         if ( event.button.button == 1 ) {
 406                                                 AttractSprite(event.button.x,
 407                                                               event.button.y);
 408                                                 mouse_pressed = 1;
 409                                         } else {
 410                                                 SDL_Rect area;
 411 
 412                                                 area.x = event.button.x-16;
 413                                                 area.y = event.button.y-16;
 414                                                 area.w = 32;
 415                                                 area.h = 32;
 416                                                 SDL_FillRect(screen, &area, 0);
 417                                                 SDL_UpdateRects(screen,1,&area);
 418                                         }
 419                                         break;
 420                                 case SDL_KEYDOWN:
 421                                         /* Any keypress quits the app... */
 422                                 case SDL_QUIT:
 423                                         done = 1;
 424                                         break;
 425                                 default:
 426                                         break;
 427                         }
 428                 }
 429         }
 430         SDL_FreeSurface(light);
 431         SDL_FreeSurface(sprite);
 432         SDL_FreeSurface(backing);
 433 
 434         /* Print out some timing information */
 435         if ( flashes > 0 ) {
 436                 printf("%d alpha blits, ~%4.4f ms per blit\n", 
 437                         flashes, (float)flashtime/flashes);
 438         }
 439         return(0);
 440 }

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