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/* ScummVM - Graphic Adventure Engine
*
* ScummVM is the legal property of its developers, whose names
* are too numerous to list here. Please refer to the COPYRIGHT
* file distributed with this source distribution.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* $URL: https://scummvm.svn.sourceforge.net/svnroot/scummvm/scummvm/trunk/engines/draci/game.cpp $
* $Id: game.cpp 45505 2009-10-29 18:15:12Z eriktorbjorn $
*
*/
#include "common/stream.h"
#include "draci/walking.h"
namespace Draci {
void WalkingMap::load(const byte *data, uint length) {
Common::MemoryReadStream mapReader(data, length);
_realWidth = mapReader.readUint16LE();
_realHeight = mapReader.readUint16LE();
_deltaX = mapReader.readUint16LE();
_deltaY = mapReader.readUint16LE();
_mapWidth = mapReader.readUint16LE();
_mapHeight = mapReader.readUint16LE();
_byteWidth = mapReader.readUint16LE();
// Set the data pointer to raw map data
_data = data + mapReader.pos();
}
bool WalkingMap::isWalkable(int x, int y) const {
// Convert to map pixels
x = x / _deltaX;
y = y / _deltaY;
int pixelIndex = _mapWidth * y + x;
int byteIndex = pixelIndex / 8;
int mapByte = _data[byteIndex];
return mapByte & (1 << pixelIndex % 8);
}
/**
* @brief For a given point, find a nearest walkable point on the walking map
*
* @param startX x coordinate of the point
* @param startY y coordinate of the point
*
* @return A Common::Point representing the nearest walkable point
*
* The algorithm was copied from the original engine for exactness.
* TODO: Study this algorithm in more detail so it can be documented properly and
* possibly improved / simplified.
*/
Common::Point WalkingMap::findNearestWalkable(int startX, int startY, Common::Rect searchRect) const {
// If the starting point is walkable, just return that
if (searchRect.contains(startX, startY) && isWalkable(startX, startY)) {
return Common::Point(startX, startY);
}
int signs[] = { 1, -1 };
const uint kSignsNum = 2;
int radius = 0;
int x, y;
int dx, dy;
int prediction;
// The place where, eventually, the result coordinates will be stored
int finalX, finalY;
// The algorithm appears to start off with an ellipse with the minor radius equal to
// zero and the major radius equal to the walking map delta (the number of pixels
// one map pixel represents). It then uses a heuristic to gradually reshape it into
// a circle (by shortening the major radius and lengthening the minor one). At each
// such resizing step, it checks some select points on the ellipse for walkability.
// It also does the same check for the ellipse perpendicular to it (rotated by 90 degrees).
while (1) {
// The default major radius
radius += _deltaX;
// The ellipse radii (minor, major) that get resized
x = 0;
y = radius;
// Heuristic variables
prediction = 1 - radius;
dx = 3;
dy = 2 * radius - 2;
do {
// The following two loops serve the purpose of checking the points on the two
// ellipses for walkability. The signs[] array is there to obliterate the need
// of writing out all combinations manually.
for (uint i = 0; i < kSignsNum; ++i) {
finalY = startY + y * signs[i];
for (uint j = 0; j < kSignsNum; ++j) {
finalX = startX + x * signs[j];
// If the current point is walkable, return it
if (searchRect.contains(finalX, finalY) && isWalkable(finalX, finalY)) {
return Common::Point(finalX, finalY);
}
}
}
if (x == y) {
// If the starting point is walkable, just return that
if (searchRect.contains(finalX, finalY) && isWalkable(finalX, finalY)) {
return Common::Point(finalX, finalY);
}
}
for (uint i = 0; i < kSignsNum; ++i) {
finalY = startY + x * signs[i];
for (uint j = 0; j < kSignsNum; ++j) {
finalX = startX + y * signs[j];
// If the current point is walkable, return it
if (searchRect.contains(finalX, finalY) && isWalkable(finalX, finalY)) {
return Common::Point(finalX, finalY);
}
}
}
// If prediction is non-negative, we need to decrease the major radius of the
// ellipse
if (prediction >= 0) {
prediction -= dy;
dy -= 2 * _deltaX;
y -= _deltaX;
}
// Increase the minor radius of the ellipse and update heuristic variables
prediction += dx;
dx += 2 * _deltaX;
x += _deltaX;
// If the current ellipse has been reshaped into a circle,
// end this loop and enlarge the radius
} while (x <= y);
}
}
}
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