From 5439c7ffebe9452f627081df7976a6e3c46ee91e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=CE=B6eh=20Matt?= <5415177+ZehMatt@users.noreply.github.com>
Date: Wed, 26 Apr 2023 18:36:10 +0300
Subject: [PATCH 1/3] Improve dirty grid rendering performance.

---
 src/openrct2/drawing/X8DrawingEngine.cpp | 33 ++++++++++++++++--------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/src/openrct2/drawing/X8DrawingEngine.cpp b/src/openrct2/drawing/X8DrawingEngine.cpp
index ca10b2309c..0fc08f0fb9 100644
--- a/src/openrct2/drawing/X8DrawingEngine.cpp
+++ b/src/openrct2/drawing/X8DrawingEngine.cpp
@@ -352,7 +352,7 @@ void X8DrawingEngine::OnDrawDirtyBlock(
 void X8DrawingEngine::ConfigureDirtyGrid()
 {
     _dirtyGrid.BlockShiftX = 7;
-    _dirtyGrid.BlockShiftY = 6;
+    _dirtyGrid.BlockShiftY = 5; // Keep column at 32 (1 << 5)
     _dirtyGrid.BlockWidth = 1 << _dirtyGrid.BlockShiftX;
     _dirtyGrid.BlockHeight = 1 << _dirtyGrid.BlockShiftY;
     _dirtyGrid.BlockColumns = (_width >> _dirtyGrid.BlockShiftX) + 1;
@@ -364,6 +364,25 @@ void X8DrawingEngine::ConfigureDirtyGrid()
 
 void X8DrawingEngine::DrawAllDirtyBlocks()
 {
+    // TODO: For optimal performance it is currently limited to a single column.
+    // The optimal approach would be to extract all dirty regions as rectangles not including
+    // parts that are not marked dirty and have the grid more fine grained.
+    // A situation like following:
+    //
+    //   0 1 2 3 4 5 6 7 8 9
+    //   1 - - - - - - - - -
+    //   2 - x x x x - - - -
+    //   3 - x x - - - - - -
+    //   4 - - - - - - - - -
+    //   5 - - - - - - - - -
+    //   6 - - - - - - - - -
+    //   7 - - - - - - - - -
+    //   8 - - - - - - - - -
+    //   9 - - - - - - - - -
+    //
+    // Would would currently redraw {2,2} to {3,5} where {3,4} and {3,5} are not dirty. Choosing to do this
+    // per column eliminates this issue but limits it to rendering just a single column at a time.
+
     for (uint32_t x = 0; x < _dirtyGrid.BlockColumns; x++)
     {
         for (uint32_t y = 0; y < _dirtyGrid.BlockRows; y++)
@@ -374,18 +393,10 @@ void X8DrawingEngine::DrawAllDirtyBlocks()
                 continue;
             }
 
-            // Determine columns
-            uint32_t xx;
-            for (xx = x; xx < _dirtyGrid.BlockColumns; xx++)
-            {
-                if (_dirtyGrid.Blocks[yOffset + xx] == 0)
-                {
-                    break;
-                }
-            }
+            // See comment above to why this is 1.
+            const uint32_t columns = 1;
 
             // Check rows
-            uint32_t columns = xx - x;
             auto rows = GetNumDirtyRows(x, y, columns);
             DrawDirtyBlocks(x, y, columns, rows);
         }

From d6b340b34d542b6bd0a2c98191e97f5dc12af3c3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=CE=B6eh=20Matt?= <5415177+ZehMatt@users.noreply.github.com>
Date: Wed, 26 Apr 2023 21:58:44 +0300
Subject: [PATCH 2/3] Fix comments

---
 src/openrct2/drawing/X8DrawingEngine.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/openrct2/drawing/X8DrawingEngine.cpp b/src/openrct2/drawing/X8DrawingEngine.cpp
index 0fc08f0fb9..3c483493a3 100644
--- a/src/openrct2/drawing/X8DrawingEngine.cpp
+++ b/src/openrct2/drawing/X8DrawingEngine.cpp
@@ -380,7 +380,7 @@ void X8DrawingEngine::DrawAllDirtyBlocks()
     //   8 - - - - - - - - -
     //   9 - - - - - - - - -
     //
-    // Would would currently redraw {2,2} to {3,5} where {3,4} and {3,5} are not dirty. Choosing to do this
+    // Would currently redraw {2,2} to {3,5} where {3,4} and {3,5} are not dirty. Choosing to do this
     // per column eliminates this issue but limits it to rendering just a single column at a time.
 
     for (uint32_t x = 0; x < _dirtyGrid.BlockColumns; x++)
@@ -393,7 +393,7 @@ void X8DrawingEngine::DrawAllDirtyBlocks()
                 continue;
             }
 
-            // See comment above to why this is 1.
+            // See comment above as to why this is 1.
             const uint32_t columns = 1;
 
             // Check rows

From 5bb267e0c9847290992c0dcc57155c4fb6bc33d8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=CE=B6eh=20Matt?= <5415177+ZehMatt@users.noreply.github.com>
Date: Wed, 26 Apr 2023 23:21:55 +0300
Subject: [PATCH 3/3] Update changelog.txt

---
 distribution/changelog.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/distribution/changelog.txt b/distribution/changelog.txt
index a495ead473..95a7ecaffc 100644
--- a/distribution/changelog.txt
+++ b/distribution/changelog.txt
@@ -16,6 +16,7 @@
 - Improved: [#19905] Add prompt before resetting shortcut keys.
 - Improved: [#19952] Add colour preset to Spiral Slide using the new colour options.
 - Improved: [#19953] Add keyboard shortcut to Keyboard Shortcuts window.
+- Improved: [#20055] Performance improvement for the software renderer.
 - Change: [OpenSFX#17] Update Hybrid RC lifthill loop.
 - Fix: [#12598] Number of holes is not set correctly when saving track designs.
 - Fix: [#13130] Android always defaulting to UK locale for language, currency and temperature.