| e14743d1 |
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| 37 | ><TH |
| 38 | COLSPAN="3" |
| 39 | ALIGN="center" |
| 40 | >SDL Library Documentation</TH |
| 41 | ></TR |
| 42 | ><TR |
| 43 | ><TD |
| 44 | WIDTH="10%" |
| 45 | ALIGN="left" |
| 46 | VALIGN="bottom" |
| 47 | ><A |
| 48 | HREF="sdlpalette.html" |
| 49 | ACCESSKEY="P" |
| 50 | >Prev</A |
| 51 | ></TD |
| 52 | ><TD |
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| 55 | VALIGN="bottom" |
| 56 | ></TD |
| 57 | ><TD |
| 58 | WIDTH="10%" |
| 59 | ALIGN="right" |
| 60 | VALIGN="bottom" |
| 61 | ><A |
| 62 | HREF="sdlsurface.html" |
| 63 | ACCESSKEY="N" |
| 64 | >Next</A |
| 65 | ></TD |
| 66 | ></TR |
| 67 | ></TABLE |
| 68 | ><HR |
| 69 | ALIGN="LEFT" |
| 70 | WIDTH="100%"></DIV |
| 71 | ><H1 |
| 72 | ><A |
| 73 | NAME="SDLPIXELFORMAT" |
| 74 | ></A |
| 75 | >SDL_PixelFormat</H1 |
| 76 | ><DIV |
| 77 | CLASS="REFNAMEDIV" |
| 78 | ><A |
| 79 | NAME="AEN3178" |
| 80 | ></A |
| 81 | ><H2 |
| 82 | >Name</H2 |
| 83 | >SDL_PixelFormat -- Stores surface format information</DIV |
| 84 | ><DIV |
| 85 | CLASS="REFSECT1" |
| 86 | ><A |
| 87 | NAME="AEN3181" |
| 88 | ></A |
| 89 | ><H2 |
| 90 | >Structure Definition</H2 |
| 91 | ><PRE |
| 92 | CLASS="PROGRAMLISTING" |
| 93 | >typedef struct SDL_PixelFormat { |
| 94 | SDL_Palette *palette; |
| 95 | Uint8 BitsPerPixel; |
| 96 | Uint8 BytesPerPixel; |
| 97 | Uint8 Rloss, Gloss, Bloss, Aloss; |
| 98 | Uint8 Rshift, Gshift, Bshift, Ashift; |
| 99 | Uint32 Rmask, Gmask, Bmask, Amask; |
| 100 | Uint32 colorkey; |
| 101 | Uint8 alpha; |
| 102 | } SDL_PixelFormat;</PRE |
| 103 | ></DIV |
| 104 | ><DIV |
| 105 | CLASS="REFSECT1" |
| 106 | ><A |
| 107 | NAME="AEN3184" |
| 108 | ></A |
| 109 | ><H2 |
| 110 | >Structure Data</H2 |
| 111 | ><DIV |
| 112 | CLASS="INFORMALTABLE" |
| 113 | ><A |
| 114 | NAME="AEN3186" |
| 115 | ></A |
| 116 | ><P |
| 117 | ></P |
| 118 | ><TABLE |
| 119 | BORDER="0" |
| 120 | CLASS="CALSTABLE" |
| 121 | ><TBODY |
| 122 | ><TR |
| 123 | ><TD |
| 124 | ALIGN="LEFT" |
| 125 | VALIGN="TOP" |
| 126 | ><TT |
| 127 | CLASS="STRUCTFIELD" |
| 128 | ><I |
| 129 | >palette</I |
| 130 | ></TT |
| 131 | ></TD |
| 132 | ><TD |
| 133 | ALIGN="LEFT" |
| 134 | VALIGN="TOP" |
| 135 | >Pointer to the <A |
| 136 | HREF="sdlpalette.html" |
| 137 | >palette</A |
| 138 | >, or <TT |
| 139 | CLASS="LITERAL" |
| 140 | >NULL</TT |
| 141 | > if the <TT |
| 142 | CLASS="STRUCTFIELD" |
| 143 | ><I |
| 144 | >BitsPerPixel</I |
| 145 | ></TT |
| 146 | >>8</TD |
| 147 | ></TR |
| 148 | ><TR |
| 149 | ><TD |
| 150 | ALIGN="LEFT" |
| 151 | VALIGN="TOP" |
| 152 | ><TT |
| 153 | CLASS="STRUCTFIELD" |
| 154 | ><I |
| 155 | >BitsPerPixel</I |
| 156 | ></TT |
| 157 | ></TD |
| 158 | ><TD |
| 159 | ALIGN="LEFT" |
| 160 | VALIGN="TOP" |
| 161 | >The number of bits used to represent each pixel in a surface. Usually 8, 16, 24 or 32.</TD |
| 162 | ></TR |
| 163 | ><TR |
| 164 | ><TD |
| 165 | ALIGN="LEFT" |
| 166 | VALIGN="TOP" |
| 167 | ><TT |
| 168 | CLASS="STRUCTFIELD" |
| 169 | ><I |
| 170 | >BytesPerPixel</I |
| 171 | ></TT |
| 172 | ></TD |
| 173 | ><TD |
| 174 | ALIGN="LEFT" |
| 175 | VALIGN="TOP" |
| 176 | >The number of bytes used to represent each pixel in a surface. Usually one to four.</TD |
| 177 | ></TR |
| 178 | ><TR |
| 179 | ><TD |
| 180 | ALIGN="LEFT" |
| 181 | VALIGN="TOP" |
| 182 | ><TT |
| 183 | CLASS="STRUCTFIELD" |
| 184 | ><I |
| 185 | >[RGBA]mask</I |
| 186 | ></TT |
| 187 | ></TD |
| 188 | ><TD |
| 189 | ALIGN="LEFT" |
| 190 | VALIGN="TOP" |
| 191 | >Binary mask used to retrieve individual color values</TD |
| 192 | ></TR |
| 193 | ><TR |
| 194 | ><TD |
| 195 | ALIGN="LEFT" |
| 196 | VALIGN="TOP" |
| 197 | ><TT |
| 198 | CLASS="STRUCTFIELD" |
| 199 | ><I |
| 200 | >[RGBA]loss</I |
| 201 | ></TT |
| 202 | ></TD |
| 203 | ><TD |
| 204 | ALIGN="LEFT" |
| 205 | VALIGN="TOP" |
| 206 | >Precision loss of each color component (2<SUP |
| 207 | >[RGBA]loss</SUP |
| 208 | >)</TD |
| 209 | ></TR |
| 210 | ><TR |
| 211 | ><TD |
| 212 | ALIGN="LEFT" |
| 213 | VALIGN="TOP" |
| 214 | ><TT |
| 215 | CLASS="STRUCTFIELD" |
| 216 | ><I |
| 217 | >[RGBA]shift</I |
| 218 | ></TT |
| 219 | ></TD |
| 220 | ><TD |
| 221 | ALIGN="LEFT" |
| 222 | VALIGN="TOP" |
| 223 | >Binary left shift of each color component in the pixel value</TD |
| 224 | ></TR |
| 225 | ><TR |
| 226 | ><TD |
| 227 | ALIGN="LEFT" |
| 228 | VALIGN="TOP" |
| 229 | ><TT |
| 230 | CLASS="STRUCTFIELD" |
| 231 | ><I |
| 232 | >colorkey</I |
| 233 | ></TT |
| 234 | ></TD |
| 235 | ><TD |
| 236 | ALIGN="LEFT" |
| 237 | VALIGN="TOP" |
| 238 | >Pixel value of transparent pixels</TD |
| 239 | ></TR |
| 240 | ><TR |
| 241 | ><TD |
| 242 | ALIGN="LEFT" |
| 243 | VALIGN="TOP" |
| 244 | ><TT |
| 245 | CLASS="STRUCTFIELD" |
| 246 | ><I |
| 247 | >alpha</I |
| 248 | ></TT |
| 249 | ></TD |
| 250 | ><TD |
| 251 | ALIGN="LEFT" |
| 252 | VALIGN="TOP" |
| 253 | >Overall surface alpha value</TD |
| 254 | ></TR |
| 255 | ></TBODY |
| 256 | ></TABLE |
| 257 | ><P |
| 258 | ></P |
| 259 | ></DIV |
| 260 | ></DIV |
| 261 | ><DIV |
| 262 | CLASS="REFSECT1" |
| 263 | ><A |
| 264 | NAME="AEN3225" |
| 265 | ></A |
| 266 | ><H2 |
| 267 | >Description</H2 |
| 268 | ><P |
| 269 | >A <SPAN |
| 270 | CLASS="STRUCTNAME" |
| 271 | >SDL_PixelFormat</SPAN |
| 272 | > describes the format of the pixel data stored at the <TT |
| 273 | CLASS="STRUCTFIELD" |
| 274 | ><I |
| 275 | >pixels</I |
| 276 | ></TT |
| 277 | > field of a <A |
| 278 | HREF="sdlsurface.html" |
| 279 | ><SPAN |
| 280 | CLASS="STRUCTNAME" |
| 281 | >SDL_Surface</SPAN |
| 282 | ></A |
| 283 | >. Every surface stores a <SPAN |
| 284 | CLASS="STRUCTNAME" |
| 285 | >SDL_PixelFormat</SPAN |
| 286 | > in the <TT |
| 287 | CLASS="STRUCTFIELD" |
| 288 | ><I |
| 289 | >format</I |
| 290 | ></TT |
| 291 | > field.</P |
| 292 | ><P |
| 293 | >If you wish to do pixel level modifications on a surface, then understanding how SDL stores its color information is essential.</P |
| 294 | ><P |
| 295 | >8-bit pixel formats are the easiest to understand. Since its an 8-bit format, we have 8 <TT |
| 296 | CLASS="STRUCTFIELD" |
| 297 | ><I |
| 298 | >BitsPerPixel</I |
| 299 | ></TT |
| 300 | > and 1 <TT |
| 301 | CLASS="STRUCTFIELD" |
| 302 | ><I |
| 303 | >BytesPerPixel</I |
| 304 | ></TT |
| 305 | >. Since <TT |
| 306 | CLASS="STRUCTFIELD" |
| 307 | ><I |
| 308 | >BytesPerPixel</I |
| 309 | ></TT |
| 310 | > is 1, all pixels are represented by a Uint8 which contains an index into <TT |
| 311 | CLASS="STRUCTFIELD" |
| 312 | ><I |
| 313 | >palette</I |
| 314 | ></TT |
| 315 | >-><TT |
| 316 | CLASS="STRUCTFIELD" |
| 317 | ><I |
| 318 | >colors</I |
| 319 | ></TT |
| 320 | >. So, to determine the color of a pixel in a 8-bit surface: we read the color index from <SPAN |
| 321 | CLASS="STRUCTNAME" |
| 322 | >surface</SPAN |
| 323 | >-><TT |
| 324 | CLASS="STRUCTFIELD" |
| 325 | ><I |
| 326 | >pixels</I |
| 327 | ></TT |
| 328 | > and we use that index to read the <A |
| 329 | HREF="sdlcolor.html" |
| 330 | ><SPAN |
| 331 | CLASS="STRUCTNAME" |
| 332 | >SDL_Color</SPAN |
| 333 | ></A |
| 334 | > structure from <SPAN |
| 335 | CLASS="STRUCTNAME" |
| 336 | >surface</SPAN |
| 337 | >-><TT |
| 338 | CLASS="STRUCTFIELD" |
| 339 | ><I |
| 340 | >format</I |
| 341 | ></TT |
| 342 | >-><TT |
| 343 | CLASS="STRUCTFIELD" |
| 344 | ><I |
| 345 | >palette</I |
| 346 | ></TT |
| 347 | >-><TT |
| 348 | CLASS="STRUCTFIELD" |
| 349 | ><I |
| 350 | >colors</I |
| 351 | ></TT |
| 352 | >. Like so: |
| 353 | <PRE |
| 354 | CLASS="PROGRAMLISTING" |
| 355 | >SDL_Surface *surface; |
| 356 | SDL_PixelFormat *fmt; |
| 357 | SDL_Color *color; |
| 358 | Uint8 index; |
| 359 | |
| 360 | . |
| 361 | . |
| 362 | |
| 363 | /* Create surface */ |
| 364 | . |
| 365 | . |
| 366 | fmt=surface->format; |
| 367 | |
| 368 | /* Check the bitdepth of the surface */ |
| 369 | if(fmt->BitsPerPixel!=8){ |
| 370 | fprintf(stderr, "Not an 8-bit surface.\n"); |
| 371 | return(-1); |
| 372 | } |
| 373 | |
| 374 | /* Lock the surface */ |
| 375 | SDL_LockSurface(surface); |
| 376 | |
| 377 | /* Get the topleft pixel */ |
| 378 | index=*(Uint8 *)surface->pixels; |
| 379 | color=fmt->palette->colors[index]; |
| 380 | |
| 381 | /* Unlock the surface */ |
| 382 | SDL_UnlockSurface(surface); |
| 383 | printf("Pixel Color-> Red: %d, Green: %d, Blue: %d. Index: %d\n", |
| 384 | color->r, color->g, color->b, index); |
| 385 | . |
| 386 | .</PRE |
| 387 | ></P |
| 388 | ><P |
| 389 | >Pixel formats above 8-bit are an entirely different experience. They are |
| 390 | considered to be "TrueColor" formats and the color information is stored in the |
| 391 | pixels themselves, not in a palette. The mask, shift and loss fields tell us |
| 392 | how the color information is encoded. The mask fields allow us to isolate each |
| 393 | color component, the shift fields tell us the number of bits to the right of |
| 394 | each component in the pixel value and the loss fields tell us the number of |
| 395 | bits lost from each component when packing 8-bit color component in a pixel. |
| 396 | <PRE |
| 397 | CLASS="PROGRAMLISTING" |
| 398 | >/* Extracting color components from a 32-bit color value */ |
| 399 | SDL_PixelFormat *fmt; |
| 400 | SDL_Surface *surface; |
| 401 | Uint32 temp, pixel; |
| 402 | Uint8 red, green, blue, alpha; |
| 403 | . |
| 404 | . |
| 405 | . |
| 406 | fmt=surface->format; |
| 407 | SDL_LockSurface(surface); |
| 408 | pixel=*((Uint32*)surface->pixels); |
| 409 | SDL_UnlockSurface(surface); |
| 410 | |
| 411 | /* Get Red component */ |
| 412 | temp=pixel&fmt->Rmask; /* Isolate red component */ |
| 413 | temp=temp>>fmt->Rshift;/* Shift it down to 8-bit */ |
| 414 | temp=temp<<fmt->Rloss; /* Expand to a full 8-bit number */ |
| 415 | red=(Uint8)temp; |
| 416 | |
| 417 | /* Get Green component */ |
| 418 | temp=pixel&fmt->Gmask; /* Isolate green component */ |
| 419 | temp=temp>>fmt->Gshift;/* Shift it down to 8-bit */ |
| 420 | temp=temp<<fmt->Gloss; /* Expand to a full 8-bit number */ |
| 421 | green=(Uint8)temp; |
| 422 | |
| 423 | /* Get Blue component */ |
| 424 | temp=pixel&fmt->Bmask; /* Isolate blue component */ |
| 425 | temp=temp>>fmt->Bshift;/* Shift it down to 8-bit */ |
| 426 | temp=temp<<fmt->Bloss; /* Expand to a full 8-bit number */ |
| 427 | blue=(Uint8)temp; |
| 428 | |
| 429 | /* Get Alpha component */ |
| 430 | temp=pixel&fmt->Amask; /* Isolate alpha component */ |
| 431 | temp=temp>>fmt->Ashift;/* Shift it down to 8-bit */ |
| 432 | temp=temp<<fmt->Aloss; /* Expand to a full 8-bit number */ |
| 433 | alpha=(Uint8)temp; |
| 434 | |
| 435 | printf("Pixel Color -> R: %d, G: %d, B: %d, A: %d\n", red, green, blue, alpha); |
| 436 | . |
| 437 | . |
| 438 | .</PRE |
| 439 | ></P |
| 440 | ></DIV |
| 441 | ><DIV |
| 442 | CLASS="REFSECT1" |
| 443 | ><A |
| 444 | NAME="AEN3252" |
| 445 | ></A |
| 446 | ><H2 |
| 447 | >See Also</H2 |
| 448 | ><P |
| 449 | ><A |
| 450 | HREF="sdlsurface.html" |
| 451 | ><SPAN |
| 452 | CLASS="STRUCTNAME" |
| 453 | >SDL_Surface</SPAN |
| 454 | ></A |
| 455 | >, |
| 456 | <A |
| 457 | HREF="sdlmaprgb.html" |
| 458 | ><TT |
| 459 | CLASS="FUNCTION" |
| 460 | >SDL_MapRGB</TT |
| 461 | ></A |
| 462 | ></P |
| 463 | ></DIV |
| 464 | ><DIV |
| 465 | CLASS="NAVFOOTER" |
| 466 | ><HR |
| 467 | ALIGN="LEFT" |
| 468 | WIDTH="100%"><TABLE |
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| 474 | ><TR |
| 475 | ><TD |
| 476 | WIDTH="33%" |
| 477 | ALIGN="left" |
| 478 | VALIGN="top" |
| 479 | ><A |
| 480 | HREF="sdlpalette.html" |
| 481 | ACCESSKEY="P" |
| 482 | >Prev</A |
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| 484 | ><TD |
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| 486 | ALIGN="center" |
| 487 | VALIGN="top" |
| 488 | ><A |
| 489 | HREF="index.html" |
| 490 | ACCESSKEY="H" |
| 491 | >Home</A |
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| 498 | HREF="sdlsurface.html" |
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| 500 | >Next</A |
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| 507 | VALIGN="top" |
| 508 | >SDL_Palette</TD |
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| 511 | ALIGN="center" |
| 512 | VALIGN="top" |
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| 514 | HREF="video.html" |
| 515 | ACCESSKEY="U" |
| 516 | >Up</A |
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| 522 | >SDL_Surface</TD |
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