From e13307a28d9de42713c352eefa25a872173be16d Mon Sep 17 00:00:00 2001
From: Duncan <duncans_pumpkin@hotmail.co.uk>
Date: Thu, 21 Oct 2021 03:51:06 +0100
Subject: [PATCH] Small cleanup of variables (#13655)

Co-authored-by: Gymnasiast <m.o.steenbeek@gmail.com>
---
 .../paint/tile_element/Paint.TileElement.cpp    | 17 ++++++-----------
 test/testpaint/Compat.cpp                       |  7 +++++++
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/openrct2/paint/tile_element/Paint.TileElement.cpp b/src/openrct2/paint/tile_element/Paint.TileElement.cpp
index bd3723be8d..8591e590b6 100644
--- a/src/openrct2/paint/tile_element/Paint.TileElement.cpp
+++ b/src/openrct2/paint/tile_element/Paint.TileElement.cpp
@@ -23,6 +23,7 @@
 #include "../../world/Banner.h"
 #include "../../world/Entrance.h"
 #include "../../world/Footpath.h"
+#include "../../world/Map.h"
 #include "../../world/Scenery.h"
 #include "../../world/Surface.h"
 #include "../Paint.h"
@@ -146,27 +147,24 @@ static void sub_68B3FB(paint_session* session, int32_t x, int32_t y)
     }
 #endif // __TESTPAINT__
 
-    int32_t dx = 0;
     switch (rotation)
     {
         case 0:
-            dx = x + y;
             break;
         case 1:
             x += 32;
-            dx = y - x;
             break;
         case 2:
             x += 32;
             y += 32;
-            dx = -(x + y);
             break;
         case 3:
             y += 32;
-            dx = x - y;
             break;
     }
-    dx >>= 1;
+
+    int32_t screenMinY = translate_3d_to_2d_with_z(rotation, { x, y, 0 }).y;
+
     // Display little yellow arrow when building footpaths?
     if ((gMapSelectFlags & MAP_SELECT_FLAG_ENABLE_ARROW) && session->MapPosition.x == gMapSelectArrowPosition.x
         && session->MapPosition.y == gMapSelectArrowPosition.y)
@@ -182,9 +180,8 @@ static void sub_68B3FB(paint_session* session, int32_t x, int32_t y)
 
         PaintAddImageAsParent(session, imageId, { 0, 0, arrowZ }, { 32, 32, -1 }, { 0, 0, arrowZ + 18 });
     }
-    int32_t bx = dx + 52;
 
-    if (bx <= dpi->y)
+    if (screenMinY + 52 <= dpi->y)
         return;
 
     const TileElement* element = tile_element; // push tile_element
@@ -210,9 +207,7 @@ static void sub_68B3FB(paint_session* session, int32_t x, int32_t y)
     }
 #endif // __TESTPAINT__
 
-    dx -= max_height + 32;
-    dx -= dpi->height;
-    if (dx >= dpi->y)
+    if (screenMinY - (max_height + 32) >= dpi->y + dpi->height)
         return;
 
     session->SpritePosition.x = x;
diff --git a/test/testpaint/Compat.cpp b/test/testpaint/Compat.cpp
index d0a62db3bf..4bd8633928 100644
--- a/test/testpaint/Compat.cpp
+++ b/test/testpaint/Compat.cpp
@@ -894,3 +894,10 @@ namespace OpenRCT2
         return nullptr;
     }
 } // namespace OpenRCT2
+
+ScreenCoordsXY translate_3d_to_2d_with_z(int32_t rotation, const CoordsXYZ& pos)
+{
+    auto rotated = pos.Rotate(rotation);
+    // Use right shift to avoid issues like #9301
+    return ScreenCoordsXY{ rotated.y - rotated.x, ((rotated.x + rotated.y) >> 1) - pos.z };
+}