From 1c97c7b61f51255baa2a42c81a8cd8cb6ef9ea1b Mon Sep 17 00:00:00 2001
From: Paul Oliver <contact@pauloliver.dev>
Date: Mon, 14 Apr 2025 17:24:56 +0200
Subject: Prevents the player from exploring unvisible areas

---
 von-newmann-2/control.lua | 63 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/von-newmann-2/control.lua b/von-newmann-2/control.lua
index 27e1190..0283aa5 100644
--- a/von-newmann-2/control.lua
+++ b/von-newmann-2/control.lua
@@ -295,14 +295,77 @@ local function on_player_created(event)
     create_roboport(center, surface, player)
 end
 
+local function on_player_changed_position(event)
+    -- Inspired by Brave New OARC.
+    -- This prevents exploration of non-visible areas of the map.
+    -- Player needs to install radars in order to explore.
+
+    local player = game.players[event.player_index]
+    local chunk_size = 32
+
+    if prev_pos[event.player_index] == nil then
+        prev_pos[event.player_index] = player.position
+    end
+
+    --print("x:", player.position.x, "y:", player.position.y, "prev_x:", prev_pos[event.player_index].x, "prev_y:", prev_pos[event.player_index].y)
+
+    local pred_dim = function(pos, prev_pos)
+        local delta = pos - prev_pos
+
+        if delta > 0 then
+            return pos + chunk_size * 2
+        elseif delta < 0 then
+            return pos - chunk_size * 2
+        end
+
+        return pos
+    end
+
+    local pred_x = pred_dim(player.position.x, prev_pos[event.player_index].x)
+    local pred_y = pred_dim(player.position.y, prev_pos[event.player_index].y)
+
+    --print("pred_x:", pred_x, "pred_y:", pred_y)
+
+    local get_player_surface = function()
+        if player.character then
+            return player.character.surface
+        else
+            return player.surface
+        end
+    end
+
+    local to_chunk_coord = function(coord)
+        return math.floor(coord / chunk_size)
+    end
+
+    if not player.force.is_chunk_visible(get_player_surface(), {to_chunk_coord(pred_x), to_chunk_coord(pred_y)}) then
+        -- teleport player to (possibly modified) prev_pos
+        player.teleport(prev_pos[event.player_index])
+        player.print("Fog of War limit! Drop a radar to extend your reach.", {sound=defines.print_sound.never})
+    end
+
+    -- Teleport back to 0,0 if current position is not visible.
+    -- This prevents the player from getting stuck in case a radar is disabled or destroyed.
+    if not player.force.is_chunk_visible(get_player_surface(), {to_chunk_coord(player.position.x), to_chunk_coord(player.position.y)}) then
+        player.teleport({0, 0})
+        player.print("Inside Fog of War! Was radar disabled or destroyed?") -- do play sound here
+    end
+
+    -- save new player position
+    prev_pos[event.player_index] = player.position
+end
+
 script.on_init(function ()
     if not remote.interfaces.freeplay then
         modEnabled = false
         return
     end
 
+    prev_pos = {}
+
     remote.call("freeplay", "set_disable_crashsite", true)
     script.on_event(defines.events.on_player_created, on_player_created)
+    script.on_event(defines.events.on_player_changed_position, on_player_changed_position)
 
     script.on_configuration_changed(updateInventory)
 end)
-- 
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