Decoded: Sopwith (1984) by David L. Clark Source file: SWSYMBOL.C Beginner friendly, line-by-line code walkthrough by MaiZure SWSYMBOL.C contains game graphics stored as CGA bitfields in low resolution. Original code: http://davidlclark.com/page/sopwith-source-code Original code with line numbers http://www.maizure.org/projects/decoded-sopwith/SWSYMBOL_linenum.txt NOTE ON CGA FORMAT IN SOPWITH In low resolution (4 color), we need 2 bits to represent each pixel. 00 = Black 01 = Cyan 10 = Magenta 11 = White Each byte represents 4 consecutive pixels in row major. To represent the four pixel row of (Black, Magenta, Cyan, White), we would create the following byte: 00 10 01 11 == 0x27. As for the color, all allied buildings are generally cyan while enemies are magenta. Changing the color of an object is as easy as inverting the color bits: NOT Black == White NOT Cyan == Magenta Objects that move freely in Sopwith, such as bombs, appear to rotate in arbitrary directions. Well the rotations aren't arbitrary, they can be in 16 distinct angles. The game doesn't perform rotations in the general sense because the operation was far too expensive in 1984. Instead, it simply stores separate images for each angle and draws the approptiate one. As you probably know, you don't need 16 separate images, if you can set a flag to draw pixels in different orders (flipping, etc). So ultimately, bombs store 8 distinct images, one for each angle, which can be flipped to produce the other 8 angles. 1 Include the main game header (sw.h) 2 BLANK 3 COMMENT 4 COMMENT 5 COMMENT 6 COMMENT 7 COMMENT 8 COMMENT 9 COMMENT 10 COMMENT 11 COMMENT 12 COMMENT 13 COMMENT 14 BLANK 15 COMMENT 16 COMMENT 17 COMMENT 18 BLANK 19 BLANK BOMB GRAPHICS 20 Defines the bomb at 8 different angles of 8x8 pixels (16 bytes/angle) 21 BLANK 22 COMMENT 23 COMMENT 24 COMMENT 25 COMMENT 26 COMMENT 27 COMMENT 28 COMMENT 29 COMMENT 30 COMMENT 31 COMMENT 32 COMMENT 33 Bytes 0-9 of the bomb at angle 0 (0 degrees) 34 Bytes 10-15 of the bomb at angle 0 (0 degrees) 35 Bytes 0-9 of the bomb at angle 1 (22.5 degrees) 36 Bytes 10-15 of the bomb at angle 1 (22.5 degrees) 37 Bytes 0-9 of the bomb at angle 2 (45 degrees) 38 Bytes 10-15 of the bomb at angle 2 (45 degrees) 39 Bytes 0-9 of the bomb at angle 3 (67.5 degrees) 40 Bytes 10-15 of the bomb at angle 3 (67.5 degrees) 41 Bytes 0-9 of the bomb at angle 4 (90 degrees) 42 Bytes 10-15 of the bomb at angle 4 (0 degrees) 43 Bytes 0-9 of the bomb at angle 5 (112.5 degrees) 44 Bytes 10-15 of the bomb at angle 6 (0 degrees) 45 Bytes 0-9 of the bomb at angle 6 (135 degrees) 46 Bytes 10-15 of the bomb at angle 7 (0 degrees) 47 Bytes 0-9 of the bomb at angle 7 (157.5 degrees) 48 Bytes 10-15 of the bomb at angle 7 (0 degrees) 49 End of bomb graphics 50 BLANK TARGET GRAPHICS 51 Defines the graphics for the four types of game targets Each is 16x16 (64 bytes) with only 1 angle needed. 52 BLANK 53 COMMENT 54 COMMENT 55 COMMENT 56 COMMENT 57 COMMENT 58 COMMENT 59 COMMENT 60 COMMENT 61 COMMENT 62 COMMENT 63 COMMENT 64 COMMENT 65 COMMENT 66 COMMENT 67 COMMENT 68 COMMENT 69 COMMENT 70 COMMENT 71 BLANK 72 BLANK 73 COMMENT 74 COMMENT 75 COMMENT 76 COMMENT 77 COMMENT 78 COMMENT 79 COMMENT 80 COMMENT 81 COMMENT 82 COMMENT 83 COMMENT 84 COMMENT 85 COMMENT 86 COMMENT 87 COMMENT 88 COMMENT 89 COMMENT 90 COMMENT 91 Bytes 0-9 of the HQ flag building 92 Bytes 10-19 of the HQ flag building 93 Bytes 20-29 of the HQ flag building 94 Bytes 30-39 of the HQ flag building 95 Bytes 40-49 of the HQ flag building 96 Bytes 50-59 of the HQ flag building 97 Bytes 60-63 of the HQ flag building 98 Bytes 0-9 of the factory building 99 Bytes 10-19 of the factory building 100 Bytes 20-29 of the factory building 101 Bytes 30-39 of the factory building 102 Bytes 40-49 of the factory building 103 Bytes 50-59 of the factory building 104 Bytes 60-63 of the factory building 105 Bytes 0-9 of the fuel tank 106 Bytes 10-19 of the fuel tank 107 Bytes 20-29 of the fuel tank 108 Bytes 30-39 of the fuel tank 109 Bytes 40-49 of the fuel tank 110 Bytes 50-59 of the fuel tank 111 Bytes 60-63 of the fuel tank 112 Bytes 0-9 of the tank 113 Bytes 10-19 of the tank 114 Bytes 20-29 of the tank 115 Bytes 30-39 of the tank 116 Bytes 40-49 of the tank 117 Bytes 50-59 of the tank 118 Bytes 60-63 of the tank 119 End of target graphics 120 BLANK DESTROYED TARGET GRAPHICS 121 Defines the graphics for a destroyed target, 16x16, only 1 angle 122 BLANK 123 COMMENT 124 COMMENT 125 COMMENT 126 COMMENT 127 COMMENT 128 COMMENT 129 COMMENT 130 COMMENT 131 COMMENT 132 COMMENT 133 COMMENT 134 COMMENT 135 COMMENT 136 COMMENT 137 COMMENT 138 COMMENT 139 COMMENT 140 COMMENT 141 COMMENT 142 Bytes 0-9 of the destroyed target 143 Bytes 10-19 of the destroyed target 144 Bytes 20-29 of the destroyed target 145 Bytes 30-39 of the destroyed target 146 Bytes 40-49 of the destroyed target 147 Bytes 50-59 of the destroyed target 148 Bytes 60-63 of the destroyed target 149 End of destroyed target graphic definition 150 BLANK EXPLOSION SHRAPNEL GRAPHICS 151 Defines 8 types of explosion shrapnel, each 8x8 for 16 bytes 152 BLANK 153 COMMENT 154 COMMENT 155 COMMENT 156 COMMENT 157 COMMENT 158 COMMENT 159 COMMENT 160 COMMENT 161 COMMENT 162 COMMENT 163 BLANK 164 COMMENT 165 COMMENT 166 COMMENT 167 COMMENT 168 COMMENT 169 COMMENT 170 COMMENT 171 COMMENT 172 COMMENT 173 COMMENT 174 BLANK 175 Bytes 0-9 of shrapnel type 0 176 Bytes 10-15 of shrapnel type 0 177 Bytes 0-9 of shrapnel type 1 178 Bytes 10-15 of shrapnel type 1 179 Bytes 0-9 of shrapnel type 2 180 Bytes 10-15 of shrapnel type 2 181 Bytes 0-9 of shrapnel type 3 182 Bytes 10-15 of shrapnel type 3 183 Bytes 0-9 of shrapnel type 4 184 Bytes 10-15 of shrapnel type 4 185 Bytes 0-9 of shrapnel type 5 186 Bytes 10-15 of shrapnel type 5 187 Bytes 0-9 of shrapnel type 6 188 Bytes 10-15 of shrapnel type 6 189 Bytes 0-9 of shrapnel type 7 190 Bytes 10-15 of shrapnel type 7 191 End of explosion shrapnel graphic definitions 192 BLANK BIRD FLOCK GRAPHICS 193 Defines the graphics for flocks of birds, with 2 frames of 16x16 194 BLANK 195 COMMENT 196 COMMENT 197 COMMENT 198 COMMENT 199 COMMENT 200 COMMENT 201 COMMENT 202 COMMENT 203 COMMENT 204 COMMENT 205 COMMENT 206 COMMENT 207 COMMENT 208 COMMENT 209 COMMENT 210 COMMENT 211 COMMENT 212 COMMENT 213 COMMENT 214 Bytes 0-9 of bird flock frame 0 215 Bytes 10-19 of bird flock frame 0 216 Bytes 20-29 of bird flock frame 0 217 Bytes 30-39 of bird flock frame 0 218 Bytes 40-49 of bird flock frame 0 219 Bytes 50-59 of bird flock frame 0 220 Bytes 60-63 of bird flock frame 0 221 Bytes 0-9 of bird flock frame 1 222 Bytes 10-19 of bird flock frame 1 223 Bytes 20-29 of bird flock frame 1 224 Bytes 30-39 of bird flock frame 1 225 Bytes 40-49 of bird flock frame 1 226 Bytes 50-59 of bird flock frame 1 227 Bytes 60-63 of bird flock frame 1 228 End of defition for bird flock graphics 229 BLANK SINGLE BIRD GRAPHICS 230 Defines the graphics for a single bird in 2 frames of 2 bytes each 231 BLANK 232 COMMENT 233 COMMENT 234 COMMENT 235 COMMENT 236 COMMENT 237 Both bird frames 238 End of single bird graphic definition 239 BLANK OXEN GRAPHICS 240 Defines the graphics for oxen in 2 frames, alive and dead (16x16 each) 241 BLANK 242 COMMENT 243 COMMENT 244 COMMENT 245 COMMENT 246 COMMENT 247 COMMENT 248 COMMENT 249 COMMENT 250 COMMENT 251 COMMENT 252 COMMENT 253 COMMENT 254 COMMENT 255 COMMENT 256 COMMENT 257 COMMENT 258 COMMENT 259 COMMENT 260 COMMENT 261 Bytes 0-9 of SchrÃ¶dinger's oxen 262 Bytes 10-19 of the living oxen 263 Bytes 20-29 of the living oxen 264 Bytes 30-39 of the living oxen 265 Bytes 40-49 of the living oxen 266 Bytes 50-59 of the living oxen 267 Bytes 60-63 of the living oxen 268 Bytes 0-9 of the dead oxen 269 Bytes 10-19 of the dead oxen 270 Bytes 20-29 of the dead oxen 271 Bytes 30-39 of the dead oxen 272 Bytes 40-49 of the dead oxen 273 Bytes 50-59 of the dead oxen 274 Bytes 60-63 of the dead oxen 275 End of defition for oxen graphics 276 BLANK GHOST GRAPHICS 277 Defines graphics for the ghosts in 1 frame of 8x8 278 BLANK 279 COMMENT 280 COMMENT 281 COMMENT 282 COMMENT 283 COMMENT 284 COMMENT 285 COMMENT 286 COMMENT 287 COMMENT 288 COMMENT 289 COMMENT 290 Bytes 0-9 of the ghost 291 Bytes 10-5 of the ghost 292 End of ghost graphic definition 293 BLANK BULLET HOLE GRAPHICS 294 Defines graphics for the bullet hole. 16x16 in 1 frame 295 BLANK 296 COMMENT 297 COMMENT 298 COMMENT 299 COMMENT 300 COMMENT 301 COMMENT 302 COMMENT 303 COMMENT 304 COMMENT 305 COMMENT 306 COMMENT 307 COMMENT 308 COMMENT 309 COMMENT 310 COMMENT 311 COMMENT 312 COMMENT 313 COMMENT 314 COMMENT 315 Bytes 0-9 of the bullet hole 316 Bytes 10-19 of the bullet hole 317 Bytes 20-29 of the bullet hole 318 Bytes 30-39 of the bullet hole 319 Bytes 40-49 of the bullet hole 320 Bytes 50-59 of the bullet hole 321 Bytes 60-63 of the bullet hole 322 End of graphics for the bullet hole 323 BLANK BIRD SPLATTER GRAPHICS 324 Defines the graphics for a bird splatter on the screen: 32x32, 256 bytes 325 BLANK 326 COMMENT 327 COMMENT 328 COMMENT 329 COMMENT 330 COMMENT 331 COMMENT 332 COMMENT 333 COMMENT 334 COMMENT 335 COMMENT 336 COMMENT 337 COMMENT 338 COMMENT 339 COMMENT 340 COMMENT 341 COMMENT 342 COMMENT 343 COMMENT 344 COMMENT 345 COMMENT 346 COMMENT 347 COMMENT 348 COMMENT 349 COMMENT 350 COMMENT 351 COMMENT 352 COMMENT 353 COMMENT 354 COMMENT 355 COMMENT 356 COMMENT 357 COMMENT 358 COMMENT 359 COMMENT 360 COMMENT 361 Bytes 0-9 of the bird splatter 362 Bytes 10-19 of the bird splatter 363 Bytes 20-29 of the bird splatter 364 Bytes 30-39 of the bird splatter 365 Bytes 40-49 of the bird splatter 366 Bytes 50-59 of the bird splatter 367 Bytes 60-69 of the bird splatter 368 Bytes 70-79 of the bird splatter 369 Bytes 80-89 of the bird splatter 370 Bytes 90-99 of the bird splatter 371 Bytes 100-109 of the bird splatter 372 Bytes 110-119 of the bird splatter 373 Bytes 120-129 of the bird splatter 374 Bytes 130-139 of the bird splatter 375 Bytes 140-149 of the bird splatter 376 Bytes 150-159 of the bird splatter 377 Bytes 160-169 of the bird splatter 378 Bytes 170-179 of the bird splatter 379 Bytes 180-189 of the bird splatter 380 Bytes 190-199 of the bird splatter 381 Bytes 200-209 of the bird splatter 382 Bytes 210-219 of the bird splatter 383 Bytes 220-229 of the bird splatter 384 Bytes 230-239 of the bird splatter 385 Bytes 240-249 of the bird splatter 386 Bytes 250-256 of the bird splatter 387 End of graphic defition for the bird splatter 388 BLANK MISSILE GRAPHICS 389 Declares the missile graphics at all 16 angles at 8x8 390 BLANK 391 COMMENT 392 BLANK 393 BLANK 394 COMMENT 395 COMMENT 396 COMMENT 397 COMMENT 398 COMMENT 399 COMMENT 400 COMMENT 401 COMMENT 402 COMMENT 403 COMMENT 404 Bytes 0-9 of the missile at angle 0 (0 degrees) 405 Bytes 10-15 of the missile at angle 0 (0 degrees) 406 Bytes 0-9 of the missile at angle 1 (22.5 degrees) 407 Bytes 10-15 of the missile at angle 1 (22.5 degrees) 408 Bytes 0-9 of the missile at angle 2 (45 degrees) 409 Bytes 10-15 of the missile at angle 2 (45 degrees) 410 Bytes 0-9 of the missile at angle 3 (67.5 degrees) 411 Bytes 10-15 of the missile at angle 3 (67.5 degrees) 412 Bytes 0-9 of the missile at angle 4 (90 degrees) 413 Bytes 10-15 of the missile at angle 4 (90 degrees) 414 Bytes 0-9 of the missile at angle 5 (112.5 degrees) 415 Bytes 10-15 of the missile at angle 5 (112.5 degrees) 416 Bytes 0-9 of the missile at angle 6 (135 degrees) 417 Bytes 10-15 of the missile at angle 6 (135 degrees) 418 Bytes 0-9 of the missile at angle 7 (157.5 degrees) 419 Bytes 10-15 of the missile at angle 7 (157.5 degrees) 420 Bytes 0-9 of the missile at angle 8 (180 degrees) 421 Bytes 10-15 of the missile at angle 8 (180 degrees) 422 Bytes 0-9 of the missile at angle 9 (202.5 degrees) 423 Bytes 10-15 of the missile at angle 9 (202.5 degrees) 424 Bytes 0-9 of the missile at angle 10 (225 degrees) 425 Bytes 10-15 of the missile at angle 10 (225 degrees) 426 Bytes 0-9 of the missile at angle 11 (247.5 degrees) 427 Bytes 10-15 of the missile at angle 11 (247.5 degrees) 428 Bytes 0-9 of the missile at angle 12 (270 degrees) 429 Bytes 10-15 of the missile at angle 12 (270 degrees) 430 Bytes 0-9 of the missile at angle 13 (292.5 degrees) 431 Bytes 10-15 of the missile at angle 13 (292.5 degrees) 432 Bytes 0-9 of the missile at angle 14 (315 degrees) 433 Bytes 10-15 of the missile at angle 14 (315 degrees) 434 Bytes 0-9 of the missile at angle 15 (337.5 degrees) 435 Bytes 10-15 of the missile at angle 15 (337.5 degrees) 436 End of missile graphics definition 437 BLANK FLARE GRAPHICS 438 Defines the graphics for flares. Two frames at 8x8 439 BLANK 440 BLANK 441 COMMENT 442 BLANK 443 COMMENT 444 COMMENT 445 COMMENT 446 COMMENT 447 COMMENT 448 COMMENT 449 COMMENT 450 COMMENT 451 COMMENT 452 COMMENT 453 Bytes 0-9 of frame 0 of the flare 454 Bytes 10-15 of frame 0 of the flare 455 Bytes 0-9 of frame 1 of the flare 456 Bytes 10-15 of frame 1 of the flare 457 End of flare graphics definition 458 BLANKÿ