From a4245bd0915a8312df5c03cbb581ca542e780317 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 3 Dec 2025 19:02:44 +0000
Subject: [PATCH] Fix LineCanvas.GetMap per-pixel allocations by reusing buffer

Applied the same allocation-free pattern from GetCellMap() to GetMap():
- Reuse List<IntersectionDefinition> buffer instead of LINQ .ToArray()
- Use CollectionsMarshal.AsSpan() to create ReadOnlySpan
- Eliminates 1,920+ allocations per border redraw (80x24)
- Reduces from O(pixels) allocations to 1 allocation total

All unit tests pass (12,055 parallelizable + 1,173 non-parallel)

Co-authored-by: tig <585482+tig@users.noreply.github.com>
---
 Terminal.Gui/Drawing/LineCanvas/LineCanvas.cs | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/Terminal.Gui/Drawing/LineCanvas/LineCanvas.cs b/Terminal.Gui/Drawing/LineCanvas/LineCanvas.cs
index 763467096..2be985764 100644
--- a/Terminal.Gui/Drawing/LineCanvas/LineCanvas.cs
+++ b/Terminal.Gui/Drawing/LineCanvas/LineCanvas.cs
@@ -211,15 +211,23 @@ public class LineCanvas : IDisposable
     {
         Dictionary<Point, Rune> map = new ();
 
+        List<IntersectionDefinition> intersectionsBufferList = [];
+
         // walk through each pixel of the bitmap
         for (int y = inArea.Y; y < inArea.Y + inArea.Height; y++)
         {
             for (int x = inArea.X; x < inArea.X + inArea.Width; x++)
             {
-                IntersectionDefinition [] intersects = _lines
-                    .Select (l => l.Intersects (x, y))
-                    .OfType<IntersectionDefinition> () // automatically filters nulls and casts
-                    .ToArray ();
+                intersectionsBufferList.Clear ();
+                foreach (var line in _lines)
+                {
+                    if (line.Intersects (x, y) is { } intersect)
+                    {
+                        intersectionsBufferList.Add (intersect);
+                    }
+                }
+                // Safe as long as the list is not modified while the span is in use.
+                ReadOnlySpan<IntersectionDefinition> intersects = CollectionsMarshal.AsSpan(intersectionsBufferList);
 
                 Rune? rune = GetRuneForIntersects (intersects);