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Amortize allocations when sorting renderables.

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Using OrderBy provides a stable sort, but internally allocates a buffer every time for storing the sort keys. We'd like to avoid this allocation, but we also can't directly use Array.Sort/Span.Sort as these are unstable sorts.

By calculating sort keys with the item index embedded, we can ensure a stable sorting result whilst being able to reuse the buffer for the sort keys across future calls.
This commit is contained in:
RoosterDragon
2025-12-12 14:21:38 +00:00
committed by Gustas Kažukauskas
parent 1539741e71
commit bcfaa44d66
1 changed files with 10 additions and 1 deletions
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11
OpenRA.Game/Graphics/WorldRenderer.cs
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@@ -12,6 +12,7 @@
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using OpenRA.Effects;
using OpenRA.Primitives;
using OpenRA.Traits;
@@ -46,6 +47,7 @@ namespace OpenRA.Graphics
readonly List<IRenderable> renderablesBuffer = [];
readonly IRenderer[] renderers;
readonly IRenderPostProcessPass[] postProcessPasses;
long[] renderablesKeysBuffer = [];
internal WorldRenderer(ModData modData, World world)
{
@@ -157,7 +159,14 @@ namespace OpenRA.Graphics
renderablesBuffer.AddRange(e.Render(this));
// Renderables must be ordered using a stable sorting algorithm to avoid flickering artefacts
foreach (var renderable in renderablesBuffer.OrderBy(RenderableZPositionComparisonKey))
if (renderablesKeysBuffer.Length < renderablesBuffer.Count)
renderablesKeysBuffer = new long[Exts.NextPowerOf2(renderablesBuffer.Count)];
for (var i = 0; i < renderablesBuffer.Count; i++)
renderablesKeysBuffer[i] = ((long)RenderableZPositionComparisonKey(renderablesBuffer[i]) << 32) + i;
var keys = renderablesKeysBuffer.AsSpan(0, renderablesBuffer.Count);
keys.Sort(CollectionsMarshal.AsSpan(renderablesBuffer));
foreach (var renderable in renderablesBuffer)
preparedRenderables.Add(renderable.PrepareRender(this));
// PERF: Reuse collection to avoid allocations.