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Unity Engine

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Unity Engine

NativeArrays

Pass pointers to NativeArray data to native code and manage the lifetime of that memory.
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NativeArray<T>
 and other types in the Unity.Collections namespace store data in memory that isn't managed by the scripting runtime. When you pass a pointer to this data to native code, you don't have to pin the buffer in memory. However, you still need to consider the lifetime of the data, which depends on the Allocator you use:

Allocator

Lifetime

Typical memory pool size

Allocator.TempThe memory is automatically cleaned up at the end of each frame.4-16 MB main thread 256 KB worker threads
Allocator.PersistentThe memory persists until the object that owns the allocation is disposed of.
Allocator.DomainThe memory persists until the C# domain is unloaded.
Allocator.TempJobThe memory persists until the object that owns the allocation is disposed of. TempJob allocations shouldn't be kept for more than four frames. If this type of memory is exhausted, then Unity falls back to a slower memory allocation method.16-64 MB
Allocator.NoneThe None allocator is used when the instance does not own the memory in the buffer it references.
Allocator.Temp
is generally the fastest way to allocate memory, but you can only use it until the end of the frame. If you allocate more memory than the amount available in the memory pool, Unity falls back to a slower type of allocation. Refer to Unmanaged C# memory for more information.
The layout of a 
NativeArray
struct is an internal detail, so you can't control how its fields are marshalled. However, you can pass a pointer to the buffer inside the array in an unsafe context.

Get a pointer to the NativeArray buffer

To get a pointer to the buffer of a 
NativeArray
, use the 
GetUnsafePtr
extension method in the 
NativeArrayUnsafeUtility
 class. When you pass the pointer to an unmanaged function, you can treat it like a C array.
The following example is an unmanaged function that takes an array of 
Color
values, which are unsigned 32-bit integers, as a parameter:
#include <stdint.h>typedef uint32_t Color;extern "C" {    void CheckerFill(Color* texture, int width, int height, int numSquares, const Color colors[], int numColors) {        const int squareSize = width / numSquares;        for (int y = 0; y < height; ++y) {            for (int x = 0; x < width; ++x) {                // Select a palette entry within the bounds of the colors array.                const int colorIndex = ((y / squareSize) + (x / squareSize)) % numColors;                texture[y * width + x] = colors[colorIndex];            }        }    }}
注意
Refer to Call unmanaged functions from managed code for information about the annotations needed to compile and call functions such as this as part of a dynamically loaded library.
You can pass a pointer to the buffer of a 
NativeArray
to this function. Using pointers in C# requires an unsafe context. For information about enabling 
unsafe
code compilation in Unity, refer to Compiling unsafe C# code.
The following code calls the unmanaged 
CheckerFill
function. The example performs the following steps:
  1. Gets a 
    NativeArray
    that contains the pixel data of a 
    Texture2D
    object.
  2. Gets a pointer to the 
    NativeArray
    buffer with 
    GetUnsafePtr
    .
  3. Calls the unmanaged 
    CheckerFill
    function to fill the texture with a checker pattern.
  4. Applies the result to the 
    Texture2D
    object.
using UnityEngine;using Unity.Collections;using System.Runtime.InteropServices;using Unity.Collections.LowLevel.Unsafe;public class NativeArrayExamples{    // For precompiled, dynamically linked libraries, change the DllImport value to the library name.    [DllImport("__Internal")]    static extern unsafe void CheckerFill(Color32* pixelDataPtr, int width, int height, int squares, [In] Color32[] colors, int numColors);    public static void FillTextureWithCheckerboard(Texture2D texture, Color32 one, Color32 two, int squaresPerSide)    {        unsafe        {            // Get the pixel data as a NativeArray.            NativeArray<Color32> pixelData = texture.GetPixelData<Color32>(0);            // Get a pointer to the NativeArray buffer.            void* pixelBuffer = pixelData.GetUnsafePtr();            // Define the color palette to choose from.            var palette = new Color32[] { one, two };            // Call the unmanaged function. Pass the palette length so it stays within the colors array.            CheckerFill((Color32*)pixelBuffer, texture.width, texture.height, squaresPerSide, palette, palette.Length);            // Apply the changes to the texture.            texture.Apply(false);        }    }}
注意
To safely access an array from unmanaged code, you must pass the number of elements it contains. In this example, the code passes 
numColors
, the length of the color palette, so the function never reads past the end of the 
colors
array. The function calculates the length of the texture array from the 
width
and 
height
parameters, so the example doesn't pass that length explicitly.

Display the generated textures in a scene

You can use the following MonoBehaviour class to call the NativeArrayExamples FillTextureWithCheckerboard method. The example adds two GameObject primitives to the scene with textures generated using the unmanaged CheckerFill function.
using UnityEngine;public class DemoNativeArray : MonoBehaviour{    void Start()    {        AddCheckeredObject(PrimitiveType.Sphere, Color.blue,  Color.yellow, Vector3.zero);        AddCheckeredObject(PrimitiveType.Cube, Color.red,  Color.white, Vector3.one);    }    void AddCheckeredObject(PrimitiveType primitive, Color colorOne, Color colorTwo, Vector3 position)    {        // Create a new texture.        Texture2D checkerboard = new Texture2D(256, 256, TextureFormat.RGBA32, false);        // Fill the texture with a checkerboard pattern using the NativeArrayExamples class.        NativeArrayExamples.FillTextureWithCheckerboard(checkerboard, colorOne, colorTwo, 8);        var go = GameObject.CreatePrimitive(primitive);        go.transform.position = position;        var litShader = Shader.Find("Universal Render Pipeline/Lit");        if (litShader != null)        {            // Create a new material using the URP Lit shader.            Material material = new Material(litShader);            // Assign the texture to the material.            material.SetTexture("_BaseMap", checkerboard);            go.GetComponent<MeshRenderer>().material = material;        }        else            Debug.LogError("Unable to load the Universal Render Pipeline/Lit shader.");    }}
Notes:
  • When you use 
    [DllImport("__Internal")]
    , the example requires the IL2CPP scripting backend and doesn't work in Play mode. To run the example in Play mode, compile the unmanaged example code as a library and change the 
    DllImport
    statements to use the library name. For more information, refer to DllImport attribute.
  • The example loads the URP Lit shader at runtime. The build process strips unused shaders and variants from a build, and can't detect runtime usage such as this. To make sure the build includes the shader, add a primitive GameObject that uses the URP Lit shader to the scene before you build.
  • Texture2D.GetPixelData<T>
     returns a 
    NativeArray
    that points to the existing memory of the texture. It doesn't allocate memory, so you don't need to dispose of the 
    NativeArray
    . Disposing of it has no effect.

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