From c440b8f9187ff5a851a560e524a23e371b54e79f Mon Sep 17 00:00:00 2001
From: Matt <m.moninger.h@gmail.com>
Date: Sun, 16 Feb 2020 14:05:00 +0100
Subject: [PATCH] Fix #10705: Apply multithreaded rendering to all viewports

---
 src/openrct2/interface/Viewport.cpp | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/openrct2/interface/Viewport.cpp b/src/openrct2/interface/Viewport.cpp
index 87098c43a4..8a8c9a569f 100644
--- a/src/openrct2/interface/Viewport.cpp
+++ b/src/openrct2/interface/Viewport.cpp
@@ -1,4 +1,4 @@
-/*****************************************************************************
+/*****************************************************************************
  * Copyright (c) 2014-2019 OpenRCT2 developers
  *
  * For a complete list of all authors, please refer to contributors.md
@@ -932,14 +932,14 @@ void viewport_paint(
 
     // make sure, the compare operation is done in int16_t to avoid the loop becoming an infiniteloop.
     // this as well as the [x += 32] in the loop causes signed integer overflow -> undefined behaviour.
-    int16_t rightBorder = dpi1.x + dpi1.width;
+    const int16_t rightBorder = dpi1.x + dpi1.width;
+    const int16_t alignedX = floor2(dpi1.x, 32);
+    const uint16_t columSize = rightBorder - alignedX;
+    const uint16_t columnCount = (columSize / 32);
 
     std::vector<paint_session*> columns;
 
     bool useMultithreading = gConfigGeneral.multithreading;
-    if (window_get_main() != nullptr && viewport != window_get_main()->viewport)
-        useMultithreading = false;
-
     if (useMultithreading && _paintJobs == nullptr)
     {
         _paintJobs = std::make_unique<JobPool>();
@@ -953,12 +953,13 @@ void viewport_paint(
     size_t index = 0;
     if (recorded_sessions != nullptr)
     {
-        const uint16_t column_count = (rightBorder - floor2(dpi1.x, 32)) / 32 + 1;
+        const uint16_t colums = rightBorder - floor2(dpi1.x, 32);
+        const uint16_t column_count = (colums / 32) + (colums % 32 > 0 ? 1 : 0);
         recorded_sessions->resize(column_count);
     }
 
     // Splits the area into 32 pixel columns and renders them
-    for (x = floor2(dpi1.x, 32); x < rightBorder; x += 32, index++)
+    for (x = alignedX; x < rightBorder; x += 32, index++)
     {
         paint_session* session = paint_session_alloc(&dpi1, viewFlags);
         columns.push_back(session);