/* Copyright (C) 2012 Wildfire Games.
* This file is part of 0 A.D.
*
* 0 A.D. 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.
*
* 0 A.D. 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 0 A.D. If not, see .
*/
#include "precompiled.h"
#include "TerritoryBoundary.h"
#include // for reverse
#include "graphics/Terrain.h"
#include "simulation2/helpers/Grid.h"
#include "simulation2/helpers/Pathfinding.h"
#include "simulation2/components/ICmpTerritoryManager.h"
std::vector CTerritoryBoundaryCalculator::ComputeBoundaries(const Grid* territory)
{
std::vector boundaries;
// Copy the territories grid so we can mess with it
Grid grid(*territory);
// Some constants for the border walk
CVector2D edgeOffsets[] = {
CVector2D(0.5f, 0.0f),
CVector2D(1.0f, 0.5f),
CVector2D(0.5f, 1.0f),
CVector2D(0.0f, 0.5f)
};
// syntactic sugar
const u8 TILE_BOTTOM = 0;
const u8 TILE_RIGHT = 1;
const u8 TILE_TOP = 2;
const u8 TILE_LEFT = 3;
const int CURVE_CW = -1;
const int CURVE_CCW = 1;
// === Find territory boundaries ===
//
// The territory boundaries delineate areas of tiles that belong to the same player, and that all have the same
// connected-to-a-root-influence-entity status (see also STerritoryBoundary for a more wordy definition). Note that the grid
// values contain bit-packed information (i.e. not just the owning player ID), so we must be careful to only compare grid
// values using the player ID and connected flag bits. The joint mask to select these is referred to as the discriminator mask.
//
// The idea is to scan the (i,j)-grid going up row by row and look for tiles that have a different territory assignment from
// the one right underneath it (or, if it's a tile on the first row, they need only have a territory assignment). These tiles
// are necessarily edge tiles of a territory, and hence a territory boundary must pass through their bottom edge. Therefore,
// we start tracing the outline of the territory starting from said bottom edge, and go CCW around the territory boundary.
// Tracing continues until the starting point is reached, at which point the boundary is complete.
//
// While tracing a boundary, every tile in which the boundary passes through the bottom edge are marked as 'processed', so that
// we know not to start a new run from these tiles when scanning continues (when the boundary is complete). This information
// is maintained in the grid values themselves by means of the 'processed' bit mask (stressing the importance of using the
// discriminator mask to compare only player ID and connected flag).
//
// Thus, we can identify the following conditions for starting a trace from a tile (i,j). Let g(i,j) indicate the
// discriminator grid value at position (i,j); then the conditions are:
// - g(i,j) != 0; the tile must not be neutral
// - j=0 or g(i,j) != g(i,j-1); the tile directly underneath it must have a different owner and/or connected flag
// - the tile must not already be marked as 'processed'
//
// Additionally, there is one more point to be made; the algorithm initially assumes it's tracing CCW around the territory.
// If it's tracing an inner edge, however, this will actually cause it to trace in the CW direction (because inner edges curve
// 'backwards' compared to the outer edges when starting the trace in the same direction). This turns out to actually be
// exactly what the renderer needs to render two territory boundaries on the same edge back-to-back (instead of overlapping
// each other).
//
// In either case, we keep track of the way the outline curves while we're tracing to determine whether we're going CW or CCW.
// If at some point we ever need to revert the winding order or external code needs to know about it explicitly, then we can
// do this by looking at a curvature value which we define to start at 0, and which is incremented by 1 for every CCW turn and
// decremented by 1 for every CW turn. Hence, a negative multiple of 4 means a CW winding order, and a positive one means CCW.
const int TERRITORY_DISCR_MASK = (ICmpTerritoryManager::TERRITORY_BLINKING_MASK | ICmpTerritoryManager::TERRITORY_PLAYER_MASK);
// Try to find an assigned tile
for (u16 j = 0; j < grid.m_H; ++j)
{
for (u16 i = 0; i < grid.m_W; ++i)
{
// saved tile state; from MSB to LSB:
// processed bit, blinking bit, player ID
u8 tileState = grid.get(i, j);
u8 tileDiscr = (tileState & TERRITORY_DISCR_MASK);
// ignore neutral tiles (note that tiles without an owner should never have the blinking bit set)
if (!tileDiscr)
continue;
bool tileProcessed = ((tileState & ICmpTerritoryManager::TERRITORY_PROCESSED_MASK) != 0);
bool tileEligible = (j == 0 || tileDiscr != (grid.get(i, j-1) & TERRITORY_DISCR_MASK));
if (tileProcessed || !tileEligible)
continue;
// Found the first tile (which must be the lowest j value of any non-zero tile);
// start at the bottom edge of it and chase anticlockwise around the border until
// we reach the starting point again
int curvature = 0; // +1 for every CCW 90 degree turn, -1 for every CW 90 degree turn; must be multiple of 4 at the end
boundaries.push_back(STerritoryBoundary());
boundaries.back().owner = (tileState & ICmpTerritoryManager::TERRITORY_PLAYER_MASK);
boundaries.back().blinking = (tileState & ICmpTerritoryManager::TERRITORY_BLINKING_MASK) != 0;
std::vector& points = boundaries.back().points;
u8 dir = TILE_BOTTOM;
u8 cdir = dir;
u16 ci = i, cj = j;
u16 maxi = (u16)(grid.m_W-1);
u16 maxj = (u16)(grid.m_H-1);
// Size of a territory tile in metres
float territoryTileSize = (Pathfinding::NAVCELL_SIZE * ICmpTerritoryManager::NAVCELLS_PER_TERRITORY_TILE).ToFloat();
while (true)
{
points.push_back((CVector2D(ci, cj) + edgeOffsets[cdir]) * territoryTileSize);
// Given that we're on an edge on a continuous boundary and aiming anticlockwise,
// we can either carry on straight or turn left or turn right, so examine each
// of the three possible cases (depending on initial direction):
switch (cdir)
{
case TILE_BOTTOM:
// mark tile as processed so we don't start a new run from it after this one is complete
ENSURE(!(grid.get(ci, cj) & ICmpTerritoryManager::TERRITORY_PROCESSED_MASK));
grid.set(ci, cj, grid.get(ci, cj) | ICmpTerritoryManager::TERRITORY_PROCESSED_MASK);
if (ci < maxi && cj > 0 && (grid.get(ci+1, cj-1) & TERRITORY_DISCR_MASK) == tileDiscr)
{
++ci;
--cj;
cdir = TILE_LEFT;
curvature += CURVE_CW;
}
else if (ci < maxi && (grid.get(ci+1, cj) & TERRITORY_DISCR_MASK) == tileDiscr)
++ci;
else
{
cdir = TILE_RIGHT;
curvature += CURVE_CCW;
}
break;
case TILE_RIGHT:
if (ci < maxi && cj < maxj && (grid.get(ci+1, cj+1) & TERRITORY_DISCR_MASK) == tileDiscr)
{
++ci;
++cj;
cdir = TILE_BOTTOM;
curvature += CURVE_CW;
}
else if (cj < maxj && (grid.get(ci, cj+1) & TERRITORY_DISCR_MASK) == tileDiscr)
++cj;
else
{
cdir = TILE_TOP;
curvature += CURVE_CCW;
}
break;
case TILE_TOP:
if (ci > 0 && cj < maxj && (grid.get(ci-1, cj+1) & TERRITORY_DISCR_MASK) == tileDiscr)
{
--ci;
++cj;
cdir = TILE_RIGHT;
curvature += CURVE_CW;
}
else if (ci > 0 && (grid.get(ci-1, cj) & TERRITORY_DISCR_MASK) == tileDiscr)
--ci;
else
{
cdir = TILE_LEFT;
curvature += CURVE_CCW;
}
break;
case TILE_LEFT:
if (ci > 0 && cj > 0 && (grid.get(ci-1, cj-1) & TERRITORY_DISCR_MASK) == tileDiscr)
{
--ci;
--cj;
cdir = TILE_TOP;
curvature += CURVE_CW;
}
else if (cj > 0 && (grid.get(ci, cj-1) & TERRITORY_DISCR_MASK) == tileDiscr)
--cj;
else
{
cdir = TILE_BOTTOM;
curvature += CURVE_CCW;
}
break;
}
// Stop when we've reached the starting point again
if (ci == i && cj == j && cdir == dir)
break;
}
ENSURE(curvature != 0 && abs(curvature) % 4 == 0);
}
}
return boundaries;
}