From 0a85ce520b292d485a622d533b300b2f60da7a26 Mon Sep 17 00:00:00 2001
From: Vasilii Rogin <vasya@rogin.ru>
Date: Tue, 18 Apr 2023 11:06:07 +0300
Subject: [PATCH] Use stack on the heap for roof fill (#263)

---
 src/tile.cc | 85 +++++++++++++++++++++++++----------------------------
 1 file changed, 40 insertions(+), 45 deletions(-)

diff --git a/src/tile.cc b/src/tile.cc
index a7e98aa..af68a39 100644
--- a/src/tile.cc
+++ b/src/tile.cc
@@ -5,6 +5,7 @@
 #include <string.h>
 
 #include <algorithm>
+#include <stack>
 
 #include "art.h"
 #include "color.h"
@@ -49,11 +50,16 @@ typedef struct UpsideDownTriangle {
     int field_8;
 } UpsideDownTriangle;
 
+struct roof_fill_task {
+    int x;
+    int y;
+};
+
 static void tileSetBorder(int windowWidth, int windowHeight, int hexGridWidth, int hexGridHeight);
 static void tileRefreshMapper(Rect* rect, int elevation);
 static void tileRefreshGame(Rect* rect, int elevation);
-static void roof_fill_on(int x, int y, int elevation);
-static void roof_fill_off(int x, int y, int elevation);
+static void roof_fill_push_task_if_in_bounds(std::stack<roof_fill_task>& tasks_stack, int x, int y);
+static void roof_fill_off_process_task(std::stack<roof_fill_task>& tasks_stack, int elevation, bool on);
 static void tileRenderRoof(int fid, int x, int y, Rect* rect, int light);
 static void _draw_grid(int tile, int elevation, Rect* rect);
 static void tileRenderFloor(int fid, int x, int y, Rect* rect);
@@ -1258,27 +1264,39 @@ void tileRenderRoofsInRect(Rect* rect, int elevation)
     }
 }
 
-// 0x4B22D0
-static void roof_fill_on(int x, int y, int elevation)
+static void roof_fill_push_task_if_in_bounds(std::stack<roof_fill_task>& tasks_stack, int x, int y)
 {
     if (x >= 0 && x < gSquareGridWidth && y >= 0 && y < gSquareGridHeight) {
-        int squareTileIndex = gSquareGridWidth * y + x;
-        int squareTile = gTileSquares[elevation]->field_0[squareTileIndex];
-        int roof = (squareTile >> 16) & 0xFFFF;
+        tasks_stack.push(roof_fill_task { x, y });
+    };
+};
 
-        int id = roof & 0xFFF;
-        if (buildFid(OBJ_TYPE_TILE, id, 0, 0, 0) != buildFid(OBJ_TYPE_TILE, 1, 0, 0, 0)) {
-            int flag = (roof & 0xF000) >> 12;
-            if ((flag & 0x01) != 0) {
+static void roof_fill_off_process_task(std::stack<roof_fill_task>& tasks_stack, int elevation, bool on)
+{
+    auto [x, y] = tasks_stack.top();
+    tasks_stack.pop();
+
+    int squareTileIndex = gSquareGridWidth * y + x;
+    int squareTile = gTileSquares[elevation]->field_0[squareTileIndex];
+    int roof = (squareTile >> 16) & 0xFFFF;
+
+    int id = roof & 0xFFF;
+    if (buildFid(OBJ_TYPE_TILE, id, 0, 0, 0) != buildFid(OBJ_TYPE_TILE, 1, 0, 0, 0)) {
+        int flag = (roof & 0xF000) >> 12;
+
+        if (on ? ((flag & 0x01) != 0) : ((flag & 0x03) == 0)) {
+            if (on) {
                 flag &= ~0x01;
-
-                gTileSquares[elevation]->field_0[squareTileIndex] = (squareTile & 0xFFFF) | (((flag << 12) | id) << 16);
-
-                roof_fill_on(x - 1, y, elevation);
-                roof_fill_on(x + 1, y, elevation);
-                roof_fill_on(x, y - 1, elevation);
-                roof_fill_on(x, y + 1, elevation);
+            } else {
+                flag |= 0x01;
             }
+
+            gTileSquares[elevation]->field_0[squareTileIndex] = (squareTile & 0xFFFF) | (((flag << 12) | id) << 16);
+
+            roof_fill_push_task_if_in_bounds(tasks_stack, x - 1, y);
+            roof_fill_push_task_if_in_bounds(tasks_stack, x + 1, y);
+            roof_fill_push_task_if_in_bounds(tasks_stack, x, y - 1);
+            roof_fill_push_task_if_in_bounds(tasks_stack, x, y + 1);
         }
     }
 }
@@ -1286,35 +1304,12 @@ static void roof_fill_on(int x, int y, int elevation)
 // 0x4B23D4
 void tile_fill_roof(int x, int y, int elevation, bool on)
 {
-    if (on) {
-        roof_fill_on(x, y, elevation);
-    } else {
-        roof_fill_off(x, y, elevation);
-    }
-}
+    std::stack<roof_fill_task> tasks_stack;
 
-// 0x4B23DC
-static void roof_fill_off(int x, int y, int elevation)
-{
-    if (x >= 0 && x < gSquareGridWidth && y >= 0 && y < gSquareGridHeight) {
-        int squareTileIndex = gSquareGridWidth * y + x;
-        int squareTile = gTileSquares[elevation]->field_0[squareTileIndex];
-        int roof = (squareTile >> 16) & 0xFFFF;
+    roof_fill_push_task_if_in_bounds(tasks_stack, x, y);
 
-        int id = roof & 0xFFF;
-        if (buildFid(OBJ_TYPE_TILE, id, 0, 0, 0) != buildFid(OBJ_TYPE_TILE, 1, 0, 0, 0)) {
-            int flag = (roof & 0xF000) >> 12;
-            if ((flag & 0x03) == 0) {
-                flag |= 0x01;
-
-                gTileSquares[elevation]->field_0[squareTileIndex] = (squareTile & 0xFFFF) | (((flag << 12) | id) << 16);
-
-                roof_fill_off(x - 1, y, elevation);
-                roof_fill_off(x + 1, y, elevation);
-                roof_fill_off(x, y - 1, elevation);
-                roof_fill_off(x, y + 1, elevation);
-            }
-        }
+    while (!tasks_stack.empty()) {
+        roof_fill_off_process_task(tasks_stack, elevation, on);
     }
 }