From 0464593a0240e6fc35a4247791a7af886938d737 Mon Sep 17 00:00:00 2001
From: gramps <gramps@llamachile.shop>
Date: Mon, 5 Oct 2026 13:34:20 -0700
Subject: [PATCH] Compositor: fast-path opaque 1:1 when source fills canvas

Handle the case where an opaque source exactly covers the destination
canvas with 1:1 dimensions (even if offsets differ in calculation). This
avoids per-pixel alpha branching and mirrors the existing memcpy fast
path. Byte-identical for opaque sources.
---
 Services/Compositor/SceneCompositor.cs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Services/Compositor/SceneCompositor.cs b/Services/Compositor/SceneCompositor.cs
index a94264e..e299058 100644
--- a/Services/Compositor/SceneCompositor.cs
+++ b/Services/Compositor/SceneCompositor.cs
@@ -624,6 +624,18 @@ public sealed class SceneCompositor
             Buffer.BlockCopy(src.BgraPixels, 0, dst, 0, dstW * dstH * 4);
             return;
         }
+        // Fully opaque source, covering entire destination canvas
+        if (op == 256 && src.IsOpaque && x0 == 0 && y0 == 0 && x1 == dstW && y1 == dstH)
+        {
+            Buffer.BlockCopy(src.BgraPixels, 0, dst, 0, dstW * dstH * 4);
+            return;
+        }
+        // Opaque source with 1:1 aligned region covering full canvas? treat same
+        if (op == 256 && src.IsOpaque && ex == 0 && ey == 0 && src.Width == dstW && src.Height == dstH)
+        {
+            Buffer.BlockCopy(src.BgraPixels, 0, dst, 0, dstW * dstH * 4);
+            return;
+        }
 
         var d = dst.AsSpan();
         var s = src.BgraPixels.AsSpan();