Why AsyncGPUReadback.RequestIntoNativeArray requires ref NativeArray<T>?

RamType0 · December 15, 2020, 3:35am

Unity-Technologies/UnityCsReference/blob/master/Runtime/Export/Graphics/AsyncGPUReadback.bindings.cs

// Unity C# reference source
// Copyright (c) Unity Technologies. For terms of use, see
// https://unity3d.com/legal/licenses/Unity_Reference_Only_License

using System;
using System.Runtime.InteropServices;
using UnityEngine;
using UnityEngine.Bindings;
using Unity.Collections.LowLevel.Unsafe;
using Unity.Collections;
using UnityEngine.Scripting;
using UnityEngine.Experimental.Rendering;

namespace UnityEngine.Rendering
{
    [NativeHeader("Runtime/Graphics/AsyncGPUReadbackManaged.h")]
    [NativeHeader("Runtime/Graphics/Texture.h")]
    [NativeHeader("Runtime/Shaders/ComputeShader.h")]
    [StructLayout(LayoutKind.Sequential)]
    [UsedByNativeCode]

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According to its implementation, it seems that we don’t need “ref” at all.
Replacing “ref” by “in” will be improve API and also preserves code level, and assembly level backwards compatibility.

Neto_Kokku · December 15, 2020, 5:34am

NativeArray is actually a value type. In that particular function it’s passed to store the output results, so the array will be modified, which goes against the purpose of “in” which is supposed to pass immutable references.

RamType0 · December 15, 2020, 7:11am

Did you see the implementation?
In implementation, the variable “output” have never been modified at all.

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Why AsyncGPUReadback.RequestIntoNativeArray requires ref NativeArray<T>?

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