[Windows] Automated build.

[0ad.git] / source / graphics / TerritoryBoundary.cpp

/* 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 <http://www.gnu.org/licenses/>.
 */

#include "precompiled.h"
#include "TerritoryBoundary.h"

#include <algorithm> // for reverse

#include "graphics/Terrain.h"
#include "simulation2/helpers/Grid.h"
#include "simulation2/helpers/Pathfinding.h"
#include "simulation2/components/ICmpTerritoryManager.h"

std::vector<STerritoryBoundary> CTerritoryBoundaryCalculator::ComputeBoundaries(const Grid<u8>* territory)
{
        std::vector<STerritoryBoundary> boundaries;

        // Copy the territories grid so we can mess with it
        Grid<u8> 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<CVector2D>& 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;
}