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// Copyright (c) Hercules Dev Team, licensed under GNU GPL.
// See the LICENSE file
// Portions Copyright (c) Athena Dev Teams
 
#include "../common/cbasetypes.h"
#include "../common/db.h"
#include "../common/malloc.h"
#include "../common/nullpo.h"
#include "../common/random.h"
#include "../common/showmsg.h"
 
#include "path.h"
#include "map.h"
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#define SET_OPEN 0
#define SET_CLOSED 1
 
#define DIR_NORTH 1
#define DIR_WEST 2
#define DIR_SOUTH 4
#define DIR_EAST 8
 
struct path_interface path_s;
 
/// @name Structures and defines for A* pathfinding
/// @{
 
/// Path node
struct path_node {
        struct path_node *parent; ///< pointer to parent (for path reconstruction)
        short x; ///< X-coordinate
        short y; ///< Y-coordinate
        short g_cost; ///< Actual cost from start to this node
        short f_cost; ///< g_cost + heuristic(this, goal)
        short flag; ///< SET_OPEN / SET_CLOSED
};
 
/// Binary heap of path nodes
BHEAP_STRUCT_DECL(node_heap, struct path_node*);
 
/// Comparator for binary heap of path nodes (minimum cost at top)
#define NODE_MINTOPCMP(i,j) ((i)->f_cost - (j)->f_cost)
 
#define calc_index(x,y) (((x)+(y)*MAX_WALKPATH) & (MAX_WALKPATH*MAX_WALKPATH-1))
 
/// Estimates the cost from (x0,y0) to (x1,y1).
/// This is inadmissible (overestimating) heuristic used by game client.
#define heuristic(x0, y0, x1, y1)       (MOVE_COST * (abs((x1) - (x0)) + abs((y1) - (y0)))) // Manhattan distance
/// @}
 
// Translates dx,dy into walking direction
static const unsigned char walk_choices [3][3] =
{
        {1,0,7},
        {2,-1,6},
        {3,4,5},
};
 
/*==========================================
 * Find the closest reachable cell, 'count' cells away from (x0,y0) in direction (dx,dy).
 * Income after the coordinates of the blow
 *------------------------------------------*/
int path_blownpos(int16 m,int16 x0,int16 y0,int16 dx,int16 dy,int count)
{
        struct map_data *md;
 
        if( !map->list[m].cell )
                return -1;
        md = &map->list[m];
 
        if( count>25 ){ //Cap to prevent too much processing...?
                ShowWarning("path_blownpos: count too many %d !\n",count);
                count=25;
        }
        if( dx > 1 || dx < -1 || dy > 1 || dy < -1 ){
                ShowError("path_blownpos: illegal dx=%d or dy=%d !\n",dx,dy);
                dx=(dx>0)?1:((dx<0)?-1:0);
                dy=(dy>0)?1:((dy<0)?-1:0);
        }
 
        while( count > 0 && (dx != 0 || dy != 0) ) {
                if( !md->getcellp(md,x0+dx,y0+dy,CELL_CHKPASS) ) {
                        break;
                }
 
                x0 += dx;
                y0 += dy;
                count--;
        }
 
        return (x0<<16)|y0; //TODO: use 'struct point' here instead?
}
 
/*==========================================
 * is ranged attack from (x0,y0) to (x1,y1) possible?
 *------------------------------------------*/
bool path_search_long(struct shootpath_data *spd,int16 m,int16 x0,int16 y0,int16 x1,int16 y1,cell_chk cell)
{
        int dx, dy;
        int wx = 0, wy = 0;
        int weight;
        struct map_data *md;
        struct shootpath_data s_spd;
 
        if( spd == NULL )
                spd = &s_spd; // use dummy output variable
 
        if (!map->list[m].cell)
                return false;
        md = &map->list[m];
 
        dx = (x1 - x0);
        if (dx < 0) {
                swap(x0, x1);
                swap(y0, y1);
                dx = -dx;
        }
        dy = (y1 - y0);
 
        spd->rx = spd->ry = 0;
        spd->len = 1;
        spd->x[0] = x0;
        spd->y[0] = y0;
 
        if (md->getcellp(md,x1,y1,cell))
                return false;
 
        if (dx > abs(dy)) {
                weight = dx;
                spd->ry = 1;
        } else {
                weight = abs(y1 - y0);
                spd->rx = 1;
        }
 
        while (x0 != x1 || y0 != y1)
        {
                if (md->getcellp(md,x0,y0,cell))
                        return false;
                wx += dx;
                wy += dy;
                if (wx >= weight) {
                        wx -= weight;
                        x0++;
                }
                if (wy >= weight) {
                        wy -= weight;
                        y0++;
                } else if (wy < 0) {
                        wy += weight;
                        y0--;
                }
                if( spd->len<MAX_WALKPATH )
                {
                        spd->x[spd->len] = x0;
                        spd->y[spd->len] = y0;
                        spd->len++;
                }
        }
 
        return true;
}
 
/// @name A* pathfinding related functions
/// @{
 
/// Pushes path_node to the binary node_heap.
/// Ensures there is enough space in array to store new element.
static void heap_push_node(struct node_heap *heap, struct path_node *node)
{
#ifndef __clang_analyzer__ // TODO: Figure out why clang's static analyzer doesn't like this
        BHEAP_ENSURE(*heap, 1, 256);
        BHEAP_PUSH(*heap, node, NODE_MINTOPCMP, swap_ptr);
#endif // __clang_analyzer__
}
 
/// Updates path_node in the binary node_heap.
static int heap_update_node(struct node_heap *heap, struct path_node *node)
{
        int i;
        ARR_FIND(0, BHEAP_LENGTH(*heap), i, BHEAP_DATA(*heap)[i] == node);
        if (i == BHEAP_LENGTH(*heap)) {
                ShowError("heap_update_node: node not found\n");
                return 1;
        }
        BHEAP_POPINDEX(*heap, i, NODE_MINTOPCMP, swap_ptr);
        BHEAP_PUSH(*heap, node, NODE_MINTOPCMP, swap_ptr);
        return 0;
}
 
/// Path_node processing in A* pathfinding.
/// Adds new node to heap and updates/re-adds old ones if necessary.
static int add_path(struct node_heap *heap, struct path_node *tp, int16 x, int16 y, int g_cost, struct path_node *parent, int h_cost)
{
        int i = calc_index(x, y);
 
        if (tp[i].x == x && tp[i].y == y) { // We processed this node before
                if (g_cost < tp[i].g_cost) { // New path to this node is better than old one
                        // Update costs and parent
                        tp[i].g_cost = g_cost;
                        tp[i].parent = parent;
                        tp[i].f_cost = g_cost + h_cost;
                        if (tp[i].flag == SET_CLOSED) {
                                heap_push_node(heap, &tp[i]); // Put it in open set again
                        }
                        else if (heap_update_node(heap, &tp[i])) {
                                return 1;
                        }
                        tp[i].flag = SET_OPEN;
                }
                return 0;
        }
 
        if (tp[i].x || tp[i].y) // Index is already taken; see `tp` array FIXME for details
                return 1;
 
        // New node
        tp[i].x = x;
        tp[i].y = y;
        tp[i].g_cost = g_cost;
        tp[i].parent = parent;
        tp[i].f_cost = g_cost + h_cost;
        tp[i].flag = SET_OPEN;
        heap_push_node(heap, &tp[i]);
        return 0;
}
///@}
 
/*==========================================
 * path search (x0,y0)->(x1,y1)
 * wpd: path info will be written here
 * flag: &1 = easy path search only
 * cell: type of obstruction to check for
 *------------------------------------------*/
bool path_search(struct walkpath_data *wpd, int16 m, int16 x0, int16 y0, int16 x1, int16 y1, int flag, cell_chk cell)
{
        register int i, j, x, y, dx, dy;
        struct map_data *md;
        struct walkpath_data s_wpd;
 
        if (wpd == NULL)
                wpd = &s_wpd; // use dummy output variable
 
        if (!map->list[m].cell)
                return false;
        md = &map->list[m];
 
#ifdef CELL_NOSTACK
        //Do not check starting cell as that would get you stuck.
        if (x0 < 0 || x0 >= md->xs || y0 < 0 || y0 >= md->ys)
#else
        if (x0 < 0 || x0 >= md->xs || y0 < 0 || y0 >= md->ys /*|| md->getcellp(md,x0,y0,cell)*/)
#endif
                return false;
 
        // Check destination cell
        if (x1 < 0 || x1 >= md->xs || y1 < 0 || y1 >= md->ys || md->getcellp(md,x1,y1,cell))
                return false;
 
        if (flag&1) {
                // Try finding direct path to target
                // Direct path goes diagonally first, then in straight line.
 
                // calculate (sgn(x1-x0), sgn(y1-y0))
                dx = ((dx = x1-x0)) ? ((dx<0) ? -1 : 1) : 0;
                dy = ((dy = y1-y0)) ? ((dy<0) ? -1 : 1) : 0;
 
                x = x0; // Current position = starting cell
                y = y0;
                i = 0;
                while( i < ARRAYLENGTH(wpd->path) )
                {
                        wpd->path[i] = walk_choices[-dy + 1][dx + 1];
                        i++;
 
                        x += dx; // Advance current position
                        y += dy;
 
                        if( x == x1 ) dx = 0; // destination x reached, no longer move along x-axis
                        if( y == y1 ) dy = 0; // destination y reached, no longer move along y-axis
 
                        if( dx == 0 && dy == 0 )
                                break; // success
                        if( md->getcellp(md,x,y,cell) )
                                break; // obstacle = failure
                }
 
                if( x == x1 && y == y1 )
                { // easy path successful.
                        wpd->path_len = i;
                        wpd->path_pos = 0;
                        return true;
                }
 
                return false; // easy path unsuccessful
        }
        else { // !(flag&1)
                // A* (A-star) pathfinding
                // We always use A* for finding walkpaths because it is what game client uses.
                // Easy pathfinding cuts corners of non-walkable cells, but client always walks around it.
               
                BHEAP_STRUCT_VAR(node_heap, open_set); // 'Open' set
 
                // FIXME: This array is too small to ensure all paths shorter than MAX_WALKPATH
                // can be found without node collision: calc_index(node1) = calc_index(node2).
                // Figure out more proper size or another way to keep track of known nodes.
                struct path_node tp[MAX_WALKPATH * MAX_WALKPATH];
                struct path_node *current, *it;
                int xs = md->xs - 1;
                int ys = md->ys - 1;
                int len = 0;
                memset(tp, 0, sizeof(tp));
 
                // Start node
                i = calc_index(x0, y0);
                tp[i].parent = NULL;
                tp[i].x      = x0;
                tp[i].y      = y0;
                tp[i].g_cost = 0;
                tp[i].f_cost = heuristic(x0, y0, x1, y1);
                tp[i].flag   = SET_OPEN;
 
                heap_push_node(&open_set, &tp[i]); // Put start node to 'open' set
                for(;;)
                {
                        int e = 0; // error flag
 
                        // Saves allowed directions for the current cell. Diagonal directions
                        // are only allowed if both directions around it are allowed. This is
                        // to prevent cutting corner of nearby wall.
                        // For example, you can only go NW from the current cell, if you can
                        // go N *and* you can go W. Otherwise you need to walk around the
                        // (corner of the) non-walkable cell.
                        int allowed_dirs = 0;
 
                        int g_cost;
 
                        if (BHEAP_LENGTH(open_set) == 0) {
                                BHEAP_CLEAR(open_set);
                                return false;
                        }
 
                        current = BHEAP_PEEK(open_set); // Look for the lowest f_cost node in the 'open' set
                        BHEAP_POP(open_set, NODE_MINTOPCMP, swap_ptr); // Remove it from 'open' set
 
                        x      = current->x;
                        y      = current->y;
                        g_cost = current->g_cost;
 
                        current->flag = SET_CLOSED; // Add current node to 'closed' set
 
                        if (x == x1 && y == y1) {
                                BHEAP_CLEAR(open_set);
                                break;
                        }
 
                        if (y < ys && !md->getcellp(md, x, y+1, cell)) allowed_dirs |= DIR_NORTH;
                        if (y >  0 && !md->getcellp(md, x, y-1, cell)) allowed_dirs |= DIR_SOUTH;
                        if (x < xs && !md->getcellp(md, x+1, y, cell)) allowed_dirs |= DIR_EAST;
                        if (x >  0 && !md->getcellp(md, x-1, y, cell)) allowed_dirs |= DIR_WEST;
 
#define chk_dir(d) ((allowed_dirs & (d)) == (d))
                        // Process neighbors of current node
                        // TODO: Processing order affects chosen path if there is more than one path with same cost.
                        // In few cases path found by server will be different than path found by game client.
                        if (chk_dir(DIR_SOUTH))
                                e += add_path(&open_set, tp, x, y-1, g_cost + MOVE_COST, current, heuristic(x, y-1, x1, y1)); // (x, y-1) 4
                        if (chk_dir(DIR_SOUTH|DIR_WEST) && !md->getcellp(md, x-1, y-1, cell))
                                e += add_path(&open_set, tp, x-1, y-1, g_cost + MOVE_DIAGONAL_COST, current, heuristic(x-1, y-1, x1, y1)); // (x-1, y-1) 3
                        if (chk_dir(DIR_WEST))
                                e += add_path(&open_set, tp, x-1, y, g_cost + MOVE_COST, current, heuristic(x-1, y, x1, y1)); // (x-1, y) 2
                        if (chk_dir(DIR_NORTH|DIR_WEST) && !md->getcellp(md, x-1, y+1, cell))
                                e += add_path(&open_set, tp, x-1, y+1, g_cost + MOVE_DIAGONAL_COST, current, heuristic(x-1, y+1, x1, y1)); // (x-1, y+1) 1
                        if (chk_dir(DIR_NORTH))
                                e += add_path(&open_set, tp, x, y+1, g_cost + MOVE_COST, current, heuristic(x, y+1, x1, y1)); // (x, y+1) 0
                        if (chk_dir(DIR_NORTH|DIR_EAST) && !md->getcellp(md, x+1, y+1, cell))
                                e += add_path(&open_set, tp, x+1, y+1, g_cost + MOVE_DIAGONAL_COST, current, heuristic(x+1, y+1, x1, y1)); // (x+1, y+1) 7
                        if (chk_dir(DIR_EAST))
                                e += add_path(&open_set, tp, x+1, y, g_cost + MOVE_COST, current, heuristic(x+1, y, x1, y1)); // (x+1, y) 6
                        if (chk_dir(DIR_SOUTH|DIR_EAST) && !md->getcellp(md, x+1, y-1, cell))
                                e += add_path(&open_set, tp, x+1, y-1, g_cost + MOVE_DIAGONAL_COST, current, heuristic(x+1, y-1, x1, y1)); // (x+1, y-1) 5
#undef chk_dir
                        if (e) {
                                BHEAP_CLEAR(open_set);
                                return false;
                        }
                }
 
                for (it = current; it->parent != NULL; it = it->parent, len++);
                if (len > sizeof(wpd->path)) {
                        return false;
                }
 
                // Recreate path
                wpd->path_len = len;
                wpd->path_pos = 0;
                for (it = current, j = len-1; j >= 0; it = it->parent, j--) {
                        dx = it->x - it->parent->x;
                        dy = it->y - it->parent->y;
                        wpd->path[j] = walk_choices[-dy + 1][dx + 1];
                }
                return true;
        } // A* end
 
        return false;
}
 
 
//Distance functions, taken from http://www.flipcode.com/articles/article_fastdistance.shtml
int check_distance(int dx, int dy, int distance)
{
#ifdef CIRCULAR_AREA
        //In this case, we just do a square comparison. Add 1 tile grace for diagonal range checks.
        return (dx*dx + dy*dy <= distance*distance + (dx&&dy?1:0));
#else
        if (dx < 0) dx = -dx;
        if (dy < 0) dy = -dy;
        return ((dx<dy?dy:dx) <= distance);
#endif
}
 
unsigned int distance(int dx, int dy)
{
#ifdef CIRCULAR_AREA
        unsigned int min, max;
 
        if ( dx < 0 ) dx = -dx;
        if ( dy < 0 ) dy = -dy;
        //There appears to be something wrong with the approximation below when either dx/dy is 0! [Skotlex]
        if ( dx == 0 ) return dy;
        if ( dy == 0 ) return dx;
 
        if ( dx < dy )
        {
                min = dx;
                max = dy;
        } else {
                min = dy;
                max = dx;
        }
   // coefficients equivalent to ( 123/128 * max ) and ( 51/128 * min )
        return ((( max << 8 ) + ( max << 3 ) - ( max << 4 ) - ( max << 1 ) +
                ( min << 7 ) - ( min << 5 ) + ( min << 3 ) - ( min << 1 )) >> 8 );
#else
        if (dx < 0) dx = -dx;
        if (dy < 0) dy = -dy;
        return (dx<dy?dy:dx);
#endif
}
void path_defaults(void) {
        path = &path_s;
       
        path->blownpos = path_blownpos;
        path->search_long = path_search_long;
        path->search = path_search;
        path->check_distance = check_distance;
        path->distance = distance;
}
 
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