From 71318dbcb35e716e99b10fcd666b1e28af5cec43 Mon Sep 17 00:00:00 2001
From: Hielke Morsink <hielke.morsink@gmail.com>
Date: Sun, 15 May 2022 00:00:47 +0200
Subject: [PATCH] Fix #17205: Crash in mapgen when base terrain is not selected

---
 distribution/changelog.txt    |  1 +
 src/openrct2/world/MapGen.cpp | 42 +++++++++++++++++++++++------------
 2 files changed, 29 insertions(+), 14 deletions(-)

diff --git a/distribution/changelog.txt b/distribution/changelog.txt
index ad6ab81e3a..12780c1b82 100644
--- a/distribution/changelog.txt
+++ b/distribution/changelog.txt
@@ -19,6 +19,7 @@
 - Fix: [#17099] Object selection thumbnail box is one pixel too tall.
 - Fix: [#17104] Changing map size does not invalidate park size.
 - Fix: [#17197] Segfault when extracting files from the GOG installer.
+- Fix: [#17205] Map generator sometimes crashes when not all standard terrain objects are available.
 
 0.4.0 (2022-04-25)
 ------------------------------------------------------------------------
diff --git a/src/openrct2/world/MapGen.cpp b/src/openrct2/world/MapGen.cpp
index 3640534ce8..2f87e65520 100644
--- a/src/openrct2/world/MapGen.cpp
+++ b/src/openrct2/world/MapGen.cpp
@@ -144,12 +144,23 @@ void mapgen_generate(mapgen_settings* settings)
     auto mapSize = settings->mapSize;
     auto waterLevel = settings->water_level;
     const auto selectedFloor = TerrainSurfaceObject::GetById(settings->floor);
-    std::string floorTexture = selectedFloor != nullptr ? std::string(selectedFloor->GetIdentifier()) : "";
+    std::string_view floorTexture = selectedFloor != nullptr ? selectedFloor->GetIdentifier() : "";
     const auto selectedEdge = TerrainEdgeObject::GetById(settings->wall);
-    std::string edgeTexture = selectedFloor != nullptr ? std::string(selectedEdge->GetIdentifier()) : "";
+    std::string_view edgeTexture = selectedFloor != nullptr ? selectedEdge->GetIdentifier() : "";
 
     if (floorTexture.empty())
-        floorTexture = BaseTerrain[util_rand() % std::size(BaseTerrain)];
+    {
+        std::vector<std::string_view> availableTerrains;
+        std::copy_if(std::begin(BaseTerrain), std::end(BaseTerrain), std::back_inserter(availableTerrains), [](auto terrain) {
+            return object_manager_get_loaded_object(ObjectEntryDescriptor(terrain)) != nullptr;
+        });
+
+        if (availableTerrains.empty())
+            // Fall back to the first available surface texture that is available in the park
+            floorTexture = TerrainSurfaceObject::GetById(0)->GetIdentifier();
+        else
+            floorTexture = availableTerrains[util_rand() % availableTerrains.size()];
+    }
 
     if (edgeTexture.empty())
     {
@@ -160,6 +171,10 @@ void mapgen_generate(mapgen_settings* settings)
             edgeTexture = "rct2.terrain_edge.ice";
         else
             edgeTexture = "rct2.terrain_edge.rock";
+
+        // Fall back to the first available edge texture that is available in the park
+        if (object_manager_get_loaded_object(ObjectEntryDescriptor(edgeTexture)) == nullptr)
+            edgeTexture = TerrainEdgeObject::GetById(0)->GetIdentifier();
     }
 
     auto floorTextureId = object_manager_get_loaded_object_entry_index(ObjectEntryDescriptor(floorTexture));
@@ -205,18 +220,17 @@ void mapgen_generate(mapgen_settings* settings)
     mapgen_set_water_level(waterLevel);
 
     // Add sandy beaches
-    std::string beachTexture = std::string(floorTexture);
-    if (settings->floor == -1 && floorTexture == "rct2.terrain_surface.grass")
+    std::string_view beachTexture = floorTexture;
+    if (settings->floor == -1 && floorTexture == "rct2.terrain_surface.grass" && (util_rand() & 1))
     {
-        switch (util_rand() % 4)
-        {
-            case 0:
-                beachTexture = "rct2.terrain_surface.sand";
-                break;
-            case 1:
-                beachTexture = "rct2.terrain_surface.sand_brown";
-                break;
-        }
+        std::vector<std::string_view> availableBeachTextures;
+        if (object_manager_get_loaded_object(ObjectEntryDescriptor("rct2.terrain_surface.sand")) != nullptr)
+            availableBeachTextures.push_back("rct2.terrain_surface.sand");
+        if (object_manager_get_loaded_object(ObjectEntryDescriptor("rct2.terrain_surface.sand_brown")) != nullptr)
+            availableBeachTextures.push_back("rct2.terrain_surface.sand_brown");
+
+        if (!availableBeachTextures.empty())
+            beachTexture = availableBeachTextures[util_rand() % availableBeachTextures.size()];
     }
     auto beachTextureId = object_manager_get_loaded_object_entry_index(ObjectEntryDescriptor(beachTexture));