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/* $Id$ */

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/** @file tile_map.cpp Global tile accessors. */

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#include "stdafx.h"

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#include "openttd.h"

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#include "tile_map.h"

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#include "core/math_func.hpp"

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/**

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 * Return the slope of a given tile

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 * @param tile Tile to compute slope of

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 * @param h    If not \c NULL, pointer to storage of z height

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 * @return Slope of the tile, except for the HALFTILE part */

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Slope GetTileSlope(TileIndex tile, uint *h)

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{

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	assert(tile < MapSize());

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	if (TileX(tile) == MapMaxX() || TileY(tile) == MapMaxY()) {

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		if (h != NULL) *h = 0;

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		return SLOPE_FLAT;

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	}

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	uint a = TileHeight(tile); // Height of the N corner

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	uint min = a; // Minimal height of all corners examined so far

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	uint b = TileHeight(tile + TileDiffXY(1, 0)); // Height of the W corner

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	if (min > b) min = b;

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	uint c = TileHeight(tile + TileDiffXY(0, 1)); // Height of the E corner

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	if (min > c) min = c;

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	uint d = TileHeight(tile + TileDiffXY(1, 1)); // Height of the S corner

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	if (min > d) min = d;

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	/* Due to the fact that tiles must connect with each other without leaving gaps, the

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	 * biggest difference in height between any corner and 'min' is between 0, 1, or 2.

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	 *

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	 * Also, there is at most 1 corner with height difference of 2.

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	 */

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	uint r = SLOPE_FLAT; // Computed slope of the tile

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	/* For each corner if not equal to minimum height:

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	 *  - set the SLOPE_STEEP flag if the difference is 2

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	 *  - add the corresponding SLOPE_X constant to the computed slope

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	 */

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	if ((a -= min) != 0) r += (--a << 4) + SLOPE_N;

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	if ((c -= min) != 0) r += (--c << 4) + SLOPE_E;

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	if ((d -= min) != 0) r += (--d << 4) + SLOPE_S;

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	if ((b -= min) != 0) r += (--b << 4) + SLOPE_W;

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	if (h != NULL) *h = min * TILE_HEIGHT;

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	return (Slope)r;

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}

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/**

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 * Get bottom height of the tile

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 * @param tile Tile to compute height of

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 * @return Minimum height of the tile */

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uint GetTileZ(TileIndex tile)

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{

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	if (TileX(tile) == MapMaxX() || TileY(tile) == MapMaxY()) return 0;

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	uint h = TileHeight(tile); // N corner

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	h = min(h, TileHeight(tile + TileDiffXY(1, 0))); // W corner

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	h = min(h, TileHeight(tile + TileDiffXY(0, 1))); // E corner

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	h = min(h, TileHeight(tile + TileDiffXY(1, 1))); // S corner

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	return h * TILE_HEIGHT;

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}

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/**

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 * Get top height of the tile

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 * @param tile Tile to compute height of

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 * @return Maximum height of the tile */

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uint GetTileMaxZ(TileIndex t)

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{

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	if (TileX(t) == MapMaxX() || TileY(t) == MapMaxY()) return 0;

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	uint h = TileHeight(t); // N corner

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	h = max(h, TileHeight(t + TileDiffXY(1, 0))); // W corner

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	h = max(h, TileHeight(t + TileDiffXY(0, 1))); // E corner

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	h = max(h, TileHeight(t + TileDiffXY(1, 1))); // S corner

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	return h * TILE_HEIGHT;

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}