(svn r26860) -Codechange: improve worst case performance of terraforming (O(n^2) -> O(n log n)) and let memory usage scale to the amount of tiles affected instead of allocating memory for the worst case scenario (patch by ic111)

1 files changed, 26 insertions, 91 deletions

diff --git a/src/terraform_cmd.cpp b/src/terraform_cmd.cpp
index 98ac1d365..ce871a407 100644
--- a/src/terraform_cmd.cpp
+++ b/src/terraform_cmd.cpp
@@ -21,40 +21,20 @@
 
 #include "table/strings.h"
 
+#include <map>
+#include <set>
+
 #include "safeguards.h"
 
-/*
- * In one terraforming command all four corners of a initial tile can be raised/lowered (though this is not available to the player).
- * The maximal amount of height modifications is achieved when raising a complete flat land from sea level to MAX_TILE_HEIGHT or vice versa.
- * This affects all corners with a manhatten distance smaller than MAX_TILE_HEIGHT to one of the initial 4 corners.
- * Their maximal amount is computed to 4 * \sum_{i=1}^{h_max} i  =  2 * h_max * (h_max + 1).
- */
-static const int TERRAFORMER_MODHEIGHT_SIZE = 2 * MAX_TILE_HEIGHT * (MAX_TILE_HEIGHT + 1);
-
-/*
- * The maximal amount of affected tiles (i.e. the tiles that incident with one of the corners above, is computed similar to
- * 1 + 4 * \sum_{i=1}^{h_max} (i+1)  =  1 + 2 * h_max + (h_max + 3).
- */
-static const int TERRAFORMER_TILE_TABLE_SIZE = 1 + 2 * MAX_TILE_HEIGHT * (MAX_TILE_HEIGHT + 3);
-
-struct TerraformerHeightMod {
-	TileIndex tile;   ///< Referenced tile.
-	byte height;      ///< New TileHeight (height of north corner) of the tile.
-};
+/** Set of tiles. */
+typedef std::set<TileIndex> TileIndexSet;
+/** Mapping of tiles to their height. */
+typedef std::map<TileIndex, int> TileIndexToHeightMap;
 
+/** State of the terraforming. */
 struct TerraformerState {
-	int modheight_count;  ///< amount of entries in "modheight".
-	int tile_table_count; ///< amount of entries in "tile_table".
-
-	/**
-	 * Dirty tiles, i.e.\ at least one corner changed.
-	 *
-	 * This array contains the tiles which are or will be marked as dirty.
-	 *
-	 * @ingroup dirty
-	 */
-	TileIndex tile_table[TERRAFORMER_TILE_TABLE_SIZE];
-	TerraformerHeightMod modheight[TERRAFORMER_MODHEIGHT_SIZE];  ///< Height modifications.
+	TileIndexSet dirty_tiles;                ///< The tiles that need to be redrawn.
+	TileIndexToHeightMap tile_to_new_height; ///< The tiles for which the height has changed.
 };
 
 TileIndex _terraform_err_tile; ///< first tile we couldn't terraform
@@ -68,14 +48,8 @@ TileIndex _terraform_err_tile; ///< first tile we couldn't terraform
  */
 static int TerraformGetHeightOfTile(const TerraformerState *ts, TileIndex tile)
 {
-	const TerraformerHeightMod *mod = ts->modheight;
-
-	for (int count = ts->modheight_count; count != 0; count--, mod++) {
-		if (mod->tile == tile) return mod->height;
-	}
-
-	/* TileHeight unchanged so far, read value from map. */
-	return TileHeight(tile);
+	TileIndexToHeightMap::const_iterator it = ts->tile_to_new_height.find(tile);
+	return it != ts->tile_to_new_height.end() ? it->second : TileHeight(tile);
 }
 
 /**
@@ -87,26 +61,7 @@ static int TerraformGetHeightOfTile(const TerraformerState *ts, TileIndex tile)
  */
 static void TerraformSetHeightOfTile(TerraformerState *ts, TileIndex tile, int height)
 {
-	/* Find tile in the "modheight" table.
-	 * Note: In a normal user-terraform command the tile will not be found in the "modheight" table.
-	 *       But during house- or industry-construction multiple corners can be terraformed at once. */
-	TerraformerHeightMod *mod = ts->modheight;
-	int count = ts->modheight_count;
-
-	while ((count > 0) && (mod->tile != tile)) {
-		mod++;
-		count--;
-	}
-
-	/* New entry? */
-	if (count == 0) {
-		assert(ts->modheight_count < TERRAFORMER_MODHEIGHT_SIZE);
-		ts->modheight_count++;
-	}
-
-	/* Finally store the new value */
-	mod->tile = tile;
-	mod->height = (byte)height;
+	ts->tile_to_new_height[tile] = height;
 }
 
 /**
@@ -118,15 +73,7 @@ static void TerraformSetHeightOfTile(TerraformerState *ts, TileIndex tile, int h
  */
 static void TerraformAddDirtyTile(TerraformerState *ts, TileIndex tile)
 {
-	int count = ts->tile_table_count;
-
-	for (TileIndex *t = ts->tile_table; count != 0; count--, t++) {
-		if (*t == tile) return;
-	}
-
-	assert(ts->tile_table_count < TERRAFORMER_TILE_TABLE_SIZE);
-
-	ts->tile_table[ts->tile_table_count++] = tile;
+	ts->dirty_tiles.insert(tile);
 }
 
 /**
@@ -247,8 +194,6 @@ CommandCost CmdTerraformLand(TileIndex tile, DoCommandFlag flags, uint32 p1, uin
 	int direction = (p2 != 0 ? 1 : -1);
 	TerraformerState ts;
 
-	ts.modheight_count = ts.tile_table_count = 0;
-
 	/* Compute the costs and the terraforming result in a model of the landscape */
 	if ((p1 & SLOPE_W) != 0 && tile + TileDiffXY(1, 0) < MapSize()) {
 		TileIndex t = tile + TileDiffXY(1, 0);
@@ -282,10 +227,8 @@ CommandCost CmdTerraformLand(TileIndex tile, DoCommandFlag flags, uint32 p1, uin
 	 * Pass == 0: Collect tileareas which are caused to be auto-cleared.
 	 * Pass == 1: Collect the actual cost. */
 	for (int pass = 0; pass < 2; pass++) {
-		TileIndex *ti = ts.tile_table;
-
-		for (int count = ts.tile_table_count; count != 0; count--, ti++) {
-			TileIndex tile = *ti;
+		for (TileIndexSet::const_iterator it = ts.dirty_tiles.begin(); it != ts.dirty_tiles.end(); it++) {
+			TileIndex tile = *it;
 
 			assert(tile < MapSize());
 			/* MP_VOID tiles can be terraformed but as tunnels and bridges
@@ -351,34 +294,26 @@ CommandCost CmdTerraformLand(TileIndex tile, DoCommandFlag flags, uint32 p1, uin
 	}
 
 	Company *c = Company::GetIfValid(_current_company);
-	if (c != NULL && (int)GB(c->terraform_limit, 16, 16) < ts.modheight_count) {
+	if (c != NULL && GB(c->terraform_limit, 16, 16) < ts.tile_to_new_height.size()) {
 		return_cmd_error(STR_ERROR_TERRAFORM_LIMIT_REACHED);
 	}
 
 	if (flags & DC_EXEC) {
 		/* change the height */
-		{
-			int count;
-			TerraformerHeightMod *mod;
+		for (TileIndexToHeightMap::const_iterator it = ts.tile_to_new_height.begin();
+				it != ts.tile_to_new_height.end(); it++) {
+			TileIndex tile = it->first;
+			int height = it->second;
 
-			mod = ts.modheight;
-			for (count = ts.modheight_count; count != 0; count--, mod++) {
-				TileIndex til = mod->tile;
-
-				SetTileHeight(til, mod->height);
-			}
+			SetTileHeight(tile, (uint)height);
 		}
 
-		/* finally mark the dirty tiles dirty */
-		{
-			int count;
-			TileIndex *ti = ts.tile_table;
-			for (count = ts.tile_table_count; count != 0; count--, ti++) {
-				MarkTileDirtyByTile(*ti);
-			}
+		/* Finally mark the dirty tiles dirty */
+		for (TileIndexSet::const_iterator it = ts.dirty_tiles.begin(); it != ts.dirty_tiles.end(); it++) {
+			MarkTileDirtyByTile(*it);
 		}
 
-		if (c != NULL) c->terraform_limit -= ts.modheight_count << 16;
+		if (c != NULL) c->terraform_limit -= ts.tile_to_new_height.size() << 16;
 	}
 	return total_cost;
 }