From bf77d1cab93467676156ebfbd5cf0ae057266e6f Mon Sep 17 00:00:00 2001
From: riperiperi <rhy3756547@hotmail.com>
Date: Sat, 8 Oct 2022 16:04:47 +0100
Subject: GPU: Pass SpanOrArray for Texture SetData to avoid copy (#3745)

* GPU: Pass SpanOrArray for Texture SetData to avoid copy

Texture data is often converted before upload, meaning that an array was allocated to perform the conversion into. However, the backend SetData methods were being passed a Span of that data, and the Multithreaded layer does `ToArray()` on it so that it can be stored for later! This method can't extract the original array, so it creates a copy.

This PR changes the type passed for textures to a new ref struct called SpanOrArray, which is backed by either a ReadOnlySpan or an array. The benefit here is that we can have a ToArray method that doesn't copy if it is originally backed by an array.

This will also avoid a copy when running the ASTC decoder.

On NieR this was taking 38% of texture upload time, which it does a _lot_ of when you move between areas, so there should be a 1.6x performance boost when strictly uploading textures. No doubt this will also improve texture streaming performance in UE4 games, and maybe a small reduction with video playback.

From the numbers, it's probably possible to improve the upload rate by a further 1.6x by performing layout conversion on GPU. I'm not sure if we could improve it further than that - multithreading conversion on CPU would probably result in memory bottleneck.

This doesn't extend to buffers, since we don't convert their data on the GPU emulator side.

* Remove implicit cast to array.
---
 Ryujinx.Common/Memory/SpanOrArray.cs | 89 ++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)
 create mode 100644 Ryujinx.Common/Memory/SpanOrArray.cs

(limited to 'Ryujinx.Common/Memory/SpanOrArray.cs')

diff --git a/Ryujinx.Common/Memory/SpanOrArray.cs b/Ryujinx.Common/Memory/SpanOrArray.cs
new file mode 100644
index 00000000..c1f06655
--- /dev/null
+++ b/Ryujinx.Common/Memory/SpanOrArray.cs
@@ -0,0 +1,89 @@
+using System;
+
+namespace Ryujinx.Common.Memory
+{
+    /// <summary>
+    /// A struct that can represent both a Span and Array.
+    /// This is useful to keep the Array representation when possible to avoid copies.
+    /// </summary>
+    /// <typeparam name="T">Element Type</typeparam>
+    public ref struct SpanOrArray<T> where T : unmanaged
+    {
+        public readonly T[] Array;
+        public readonly ReadOnlySpan<T> Span;
+
+        /// <summary>
+        /// Create a new SpanOrArray from an array.
+        /// </summary>
+        /// <param name="array">Array to store</param>
+        public SpanOrArray(T[] array)
+        {
+            Array = array;
+            Span = ReadOnlySpan<T>.Empty;
+        }
+
+        /// <summary>
+        /// Create a new SpanOrArray from a readonly span.
+        /// </summary>
+        /// <param name="array">Span to store</param>
+        public SpanOrArray(ReadOnlySpan<T> span)
+        {
+            Array = null;
+            Span = span;
+        }
+
+        /// <summary>
+        /// Return the contained array, or convert the span if necessary.
+        /// </summary>
+        /// <returns>An array containing the data</returns>
+        public T[] ToArray()
+        {
+            return Array ?? Span.ToArray();
+        }
+
+        /// <summary>
+        /// Return a ReadOnlySpan from either the array or ReadOnlySpan.
+        /// </summary>
+        /// <returns>A ReadOnlySpan containing the data</returns>
+        public ReadOnlySpan<T> AsSpan()
+        {
+            return Array ?? Span;
+        }
+
+        /// <summary>
+        /// Cast an array to a SpanOrArray.
+        /// </summary>
+        /// <param name="array">Source array</param>
+        public static implicit operator SpanOrArray<T>(T[] array)
+        {
+            return new SpanOrArray<T>(array);
+        }
+
+        /// <summary>
+        /// Cast a ReadOnlySpan to a SpanOrArray.
+        /// </summary>
+        /// <param name="span">Source ReadOnlySpan</param>
+        public static implicit operator SpanOrArray<T>(ReadOnlySpan<T> span)
+        {
+            return new SpanOrArray<T>(span);
+        }
+
+        /// <summary>
+        /// Cast a Span to a SpanOrArray.
+        /// </summary>
+        /// <param name="span">Source Span</param>
+        public static implicit operator SpanOrArray<T>(Span<T> span)
+        {
+            return new SpanOrArray<T>(span);
+        }
+
+        /// <summary>
+        /// Cast a SpanOrArray to a ReadOnlySpan
+        /// </summary>
+        /// <param name="spanOrArray">Source SpanOrArray</param>
+        public static implicit operator ReadOnlySpan<T>(SpanOrArray<T> spanOrArray)
+        {
+            return spanOrArray.AsSpan();
+        }
+    }
+}
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