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(svn r24132) -Change [FS#4713]: Improve randomness of tile order in the tile loop. (monoid)

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michi_cc 2012-04-17 19:43:43 +00:00
parent d78c4d9ee3
commit 2eae02db59
4 changed files with 36 additions and 20 deletions
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1
src/genworld.cpp
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@ -159,6 +159,7 @@ static void _GenerateWorld(void *)
SetGeneratingWorldProgress(GWP_RUNTILELOOP, 0x500);
for (i = 0; i < 0x500; i++) {
RunTileLoop();
_tick_counter++;
IncreaseGeneratingWorldProgress(GWP_RUNTILELOOP);
}

47
src/landscape.cpp
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@ -712,32 +712,43 @@ CommandCost CmdClearArea(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
TileIndex _cur_tileloop_tile;
#define TILELOOP_BITS 4
#define TILELOOP_SIZE (1 << TILELOOP_BITS)
#define TILELOOP_ASSERTMASK ((TILELOOP_SIZE - 1) + ((TILELOOP_SIZE - 1) << MapLogX()))
#define TILELOOP_CHKMASK (((1 << (MapLogX() - TILELOOP_BITS))-1) << TILELOOP_BITS)
/**
* Gradually iterate over all tiles on the map, calling their TileLoopProcs once every 256 ticks.
*/
void RunTileLoop()
{
TileIndex tile = _cur_tileloop_tile;
/* The pseudorandom sequence of tiles is generated using a Galois linear feedback
* shift register (LFSR). This allows a deterministic pseudorandom ordering, but
* still with minimal state and fast iteration. */
assert((tile & ~TILELOOP_ASSERTMASK) == 0);
uint count = (MapSizeX() / TILELOOP_SIZE) * (MapSizeY() / TILELOOP_SIZE);
do {
/* Maximal length LFSR feedback terms, from 12-bit (for 64x64 maps) to 22-bit (for 2048x2048 maps).
* Extracted from http://www.ece.cmu.edu/~koopman/lfsr/ */
static const uint32 feedbacks[] = {
0xD8F, 0x1296, 0x2496, 0x4357, 0x8679, 0x1030E, 0x206CD, 0x403FE, 0x807B8, 0x1004B2, 0x2006A8
};
const uint32 feedback = feedbacks[MapLogX() + MapLogY() - 12];
/* We update every tile every 256 ticks, so divide the map size by 2^8 = 256 */
uint count = 1 << (MapLogX() + MapLogY() - 8);
TileIndex tile = _cur_tileloop_tile;
/* The LFSR cannot have a zeroed state. */
assert(tile != 0);
/* Manually update tile 0 every 256 ticks - the LFSR never iterates over it itself. */
if (_tick_counter % 256 == 0) {
_tile_type_procs[GetTileType(0)]->tile_loop_proc(0);
count--;
}
while (count--) {
_tile_type_procs[GetTileType(tile)]->tile_loop_proc(tile);
if (TileX(tile) < MapSizeX() - TILELOOP_SIZE) {
tile += TILELOOP_SIZE; // no overflow
} else {
tile = TILE_MASK(tile - TILELOOP_SIZE * (MapSizeX() / TILELOOP_SIZE - 1) + TileDiffXY(0, TILELOOP_SIZE)); // x would overflow, also increase y
/* Get the next tile in sequence using a Galois LFSR. */
tile = (tile >> 1) ^ (-(int32)(tile & 1) & feedback);
}
} while (--count != 0);
assert((tile & ~TILELOOP_ASSERTMASK) == 0);
tile += 9;
if (tile & TILELOOP_CHKMASK) {
tile = (tile + MapSizeX()) & TILELOOP_ASSERTMASK;
}
_cur_tileloop_tile = tile;
}

2
src/misc.cpp
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@ -59,7 +59,7 @@ void InitializeGame(uint size_x, uint size_y, bool reset_date, bool reset_settin
_pause_mode = PM_UNPAUSED;
_fast_forward = 0;
_tick_counter = 0;
_cur_tileloop_tile = 0;
_cur_tileloop_tile = 1;
_thd.redsq = INVALID_TILE;
if (reset_settings) MakeNewgameSettingsLive();

4
src/saveload/afterload.cpp
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@ -483,6 +483,10 @@ bool AfterLoadGame()
TileIndex map_size = MapSize();
extern TileIndex _cur_tileloop_tile; // From landscape.cpp.
/* The LFSR used in RunTileLoop iteration cannot have a zeroed state, make it non-zeroed. */
if (_cur_tileloop_tile == 0) _cur_tileloop_tile = 1;
if (IsSavegameVersionBefore(98)) GamelogOldver();
GamelogTestRevision();