diff options
Diffstat (limited to 'src/landscape.cpp')
| -rw-r--r-- | src/landscape.cpp | 47 |
1 files changed, 29 insertions, 18 deletions
diff --git a/src/landscape.cpp b/src/landscape.cpp index caa75ef27..a4b12f857 100644 --- a/src/landscape.cpp +++ b/src/landscape.cpp @@ -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() { + /* 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. */ + + /* 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); - assert((tile & ~TILELOOP_ASSERTMASK) == 0); - uint count = (MapSizeX() / TILELOOP_SIZE) * (MapSizeY() / TILELOOP_SIZE); - do { - _tile_type_procs[GetTileType(tile)]->tile_loop_proc(tile); + /* 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--; + } - 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 - } - } while (--count != 0); - assert((tile & ~TILELOOP_ASSERTMASK) == 0); + while (count--) { + _tile_type_procs[GetTileType(tile)]->tile_loop_proc(tile); - tile += 9; - if (tile & TILELOOP_CHKMASK) { - tile = (tile + MapSizeX()) & TILELOOP_ASSERTMASK; + /* Get the next tile in sequence using a Galois LFSR. */ + tile = (tile >> 1) ^ (-(int32)(tile & 1) & feedback); } + _cur_tileloop_tile = tile; } |