DrawDungeon2: Implement pathfinding functions

include/dungeon/dgn.h

@@ -91,6 +91,7 @@ struct dgn_cell {
 	int32_t south_event2;
 	int32_t east_event2;
 	int32_t west_event2;
+	int pathfinding_cost;
 	struct dgn_cell **visible_cells;
 };
 
@@ -139,5 +140,6 @@ static inline bool dgn_is_in_map(struct dgn *dgn, uint32_t x, uint32_t y, uint32
 struct dgn_cell **dgn_get_visible_cells(struct dgn *dgn, int x, int y, int z, int *nr_cells_out);
 
 struct dgn *dgn_generate_drawdungeon2(int level);
+void dgn_paint_step(struct dgn *dgn, int x, int y);
 
 #endif /* SYSTEM4_DGN_H */

include/dungeon/dungeon.h

@@ -76,6 +76,7 @@ void dungeon_set_walked_all(int surface);
 int dungeon_calc_conquer(int surface);
 bool dungeon_load_walk_data(int surface, int map, struct page **page);
 bool dungeon_save_walk_data(int surface, int map, struct page **page);
+void dungeon_paint_step(int surface, int x, int y, int z);
 
 struct dungeon_context *dungeon_get_context(int surface);
 

src/dungeon/dgn.c

@@ -559,6 +559,7 @@ struct dgn *dgn_generate_drawdungeon2(int level)
 			cell->roof_orientation = -1;
 			cell->roof_texture = -1;
 			cell->roof_underside_texture = -1;
+			cell->pathfinding_cost = -1;
 
 			if (map[x][z] == '#') {
 				continue;
@@ -593,3 +594,62 @@ struct dgn *dgn_generate_drawdungeon2(int level)
 	}
 	return dgn;
 }
+
+// Set pathfinding_cost for each cell on the shortest path to the exit cell
+void dgn_paint_step(struct dgn *dgn, int start_x, int start_y)
+{
+	int nr_cells = dgn_nr_cells(dgn);
+	for (int i = 0; i < nr_cells; i++) {
+		dgn->cells[i].pathfinding_cost = -1;
+	}
+
+	// BFS.
+	short dist[DD2_MAP_WIDTH][DD2_MAP_HEIGHT] = {0};
+	struct { int8_t x, y; } prev[DD2_MAP_WIDTH][DD2_MAP_HEIGHT];
+	struct point_list queue = {0};
+	int queue_ptr = 0;
+
+	dist[start_x][start_y] = 1;
+	point_list_add(&queue, start_x, start_y);
+
+	while (queue_ptr < queue.size) {
+		int cx = queue.p[queue_ptr].x;
+		int cy = queue.p[queue_ptr].y;
+		if (cx == dgn->exit_x && cy == dgn->exit_y)
+			break;
+		queue_ptr++;
+
+		// Add adjacent cells to the queue
+		const int dx_offsets[] = {0, 0, -1, 1};
+		const int dy_offsets[] = {-1, 1, 0, 0};
+		for (int i = 0; i < 4; i++) {
+			int nx = cx + dx_offsets[i];
+			int ny = cy + dy_offsets[i];
+			if (nx >= 0 && nx < DD2_MAP_WIDTH && ny >= 0 && ny < DD2_MAP_HEIGHT &&
+			    !dist[nx][ny] && dgn->cells[dgn_cell_index(dgn, nx, 0, ny)].floor >= 0) {
+				dist[nx][ny] = dist[cx][cy] + 1;
+				prev[nx][ny].x = cx;
+				prev[nx][ny].y = cy;
+				point_list_add(&queue, nx, ny);
+			}
+		}
+	}
+	if (queue_ptr >= queue.size) {
+		// The exit is not reachable from the start (should not happen)
+		return;
+	}
+
+	// Backtrack from the exit to the start to paint the path
+	int x = dgn->exit_x;
+	int y = dgn->exit_y;
+	for (;;) {
+		struct dgn_cell *cell = &dgn->cells[dgn_cell_index(dgn, x, 0, y)];
+		cell->pathfinding_cost = dist[x][y] - 1;  // -1 to make the start cell 0
+		if (x == start_x && y == start_y)
+			break;
+		int px = prev[x][y].x;
+		int py = prev[x][y].y;
+		x = px;
+		y = py;
+	}
+}

src/dungeon/dungeon.c

@@ -567,6 +567,14 @@ bool dungeon_save_walk_data(int surface, int map, struct page **page)
 	}
 }
 
+void dungeon_paint_step(int surface, int x, int y, int z)
+{
+	struct dungeon_context *ctx = dungeon_get_context(surface);
+	if (!ctx || !ctx->dgn)
+		return;
+	dgn_paint_step(ctx->dgn, x, z);
+}
+
 static cJSON *dungeon_to_json(struct sact_sprite *sp, bool verbose)
 {
 	cJSON *obj, *cam;

src/hll/DrawDungeon.c

@@ -413,16 +413,15 @@ static void DrawDungeon2_GetExitPos(int surface, int *x, int *y)
 	*y = ctx->dgn->exit_y;
 }
 
-//void DrawDungeon2_PaintStep(int nSurface, int nX, int nY, int nZ);
-//int DrawDungeon2_GetMapStep(int nSurface, int nX, int nY, int nZ);
+CELL_GETTER(DrawDungeon2_GetMapStep, -1, cell->pathfinding_cost);
 
 HLL_LIBRARY(DrawDungeon2,
 	    HLL_EXPORT(Init, DrawDungeon2_Init),
 	    DRAW_DUNGEON_EXPORTS,
 	    HLL_EXPORT(GetPlayerStartPos, DrawDungeon2_GetPlayerStartPos),
 	    HLL_EXPORT(GetExitPos, DrawDungeon2_GetExitPos),
-	    HLL_TODO_EXPORT(PaintStep, DrawDungeon2_PaintStep),
-	    HLL_TODO_EXPORT(GetMapStep, DrawDungeon2_GetMapStep)
+	    HLL_EXPORT(PaintStep, dungeon_paint_step),
+	    HLL_EXPORT(GetMapStep, DrawDungeon2_GetMapStep)
 	    );
 
 static void DrawDungeon14_SetRasterScroll(int surface, int type)