How to write Unity RenderTexture from iOS plug in?

I write iOS plug in to integrate MetalFX Spatial Upscaling to Unity URP project.

C# Code in Unity: namespace UnityEngine.Rendering.Universal { /// <summary> /// Renders the post-processing effect stack. /// </summary> internal class PostProcessPass : ScriptableRenderPass { RenderTexture _dstRT = null; [DllImport ("__Internal")] private static extern void MetalFX_SpatialScaling (IntPtr srcTexture, IntPtr dstTexture, IntPtr outTexture); } }

void RenderFinalPass(CommandBuffer cmd, ref RenderingData renderingData) { // ...... case ImageUpscalingFilter.MetalFX: { var upscaleRtDesc = tempRtDesc; upscaleRtDesc.width = cameraData.pixelWidth; upscaleRtDesc.height = cameraData.pixelHeight;

                            RenderingUtils.ReAllocateIfNeeded(ref m_UpscaledTarget, upscaleRtDesc, FilterMode.Point, TextureWrapMode.Clamp, name: "_UpscaledTexture");
                            var metalfxInputSize = new Vector2(cameraData.cameraTargetDescriptor.width, cameraData.cameraTargetDescriptor.height);
                            if (_dstRT == null)
                            {
                                _dstRT = new RenderTexture(upscaleRtDesc.width, upscaleRtDesc.height, 0, RenderTextureFormat.ARGB32);
                                _dstRT.Create();
                            }
                            // call native plugin
                            cmd.SetRenderTarget(m_UpscaledTarget, RenderBufferLoadAction.DontCare, RenderBufferStoreAction.Store, RenderBufferLoadAction.DontCare, RenderBufferStoreAction.DontCare);
                            MetalFX_SpatialScaling(sourceTex.rt.GetNativeTexturePtr(), m_UpscaledTarget.rt.GetNativeTexturePtr(), _dstRT.GetNativeTexturePtr());
                            Graphics.CopyTexture(_dstRT, m_UpscaledTarget.rt);
                            sourceTex = m_UpscaledTarget;
                            PostProcessUtils.SetSourceSize(cmd, upscaleRtDesc);
                            break;
                        }
  // .....

}

Objective-c Code in iOS: head file: #import <Foundation/Foundation.h> #import <MetalFX/MTLFXSpatialScaler.h>

@protocol MTLTexture; @protocol MTLDevice;

API_AVAILABLE(ios(16.0)) @interface MetalFXDelegate : NSObject { int mode; id<MTLDevice> _device; id <MTLCommandQueue> _commandQueue; id <MTLTexture> _outTexture; id <MTLFXSpatialScaler> _mfxSpatialScaler; id <MTLBlitCommandEncoder> _mfxSpatialEncoder; };

• (void)SpatialScaling: (MTLTextureRef) srcTexture dstTexure: (MTLTextureRef) dstTexture outTexure: (MTLTextureRef) outTexture;
• (void)saveTexturePNG: (MTLTextureRef) texture url: (CFURLRef) url; @end

m file:

#import "MetalFXOC.h"

@implementation MetalFXDelegate

• (id)init

{ self = [super init]; return self; }

static MetalFXDelegate* delegateObject = nil;

• (void)SpatialScaling: (MTLTextureRef) srcTexture dstTexture: (MTLTextureRef) dstTexture outTexture: (MTLTextureRef) outTexture { int width = (int)srcTexture.width; int height = (int)srcTexture.height; int dstWidth = (int)dstTexture.width; int dstHeight = (int)dstTexture.height;

  if (_mfxSpatialScaler == nil) { MTLFXSpatialScalerDescriptor* desc; desc = [[MTLFXSpatialScalerDescriptor alloc]init]; desc.inputWidth = width; desc.inputHeight = height; desc.outputWidth = dstWidth; ///_screenWidth desc.outputHeight = dstHeight; ///_screenHeight desc.colorTextureFormat = srcTexture.pixelFormat; desc.outputTextureFormat = dstTexture.pixelFormat; if (@available(iOS 16.0, *)) { desc.colorProcessingMode = MTLFXSpatialScalerColorProcessingModePerceptual; } else { // Fallback on earlier versions }

    _device = MTLCreateSystemDefaultDevice();
    _mfxSpatialScaler = [desc newSpatialScalerWithDevice:_device];
    if (_mfxSpatialScaler == nil) {
        return;
    }
    _commandQueue = [_device newCommandQueue];
    
    MTLTextureDescriptor *texdesc   = [[MTLTextureDescriptor alloc] init];
    texdesc.width = (int)dstTexture.width;
    texdesc.height = (int)dstTexture.height;
    texdesc.storageMode = MTLStorageModePrivate;
    texdesc.usage = MTLTextureUsageRenderTarget | MTLTextureUsageShaderRead | MTLTextureUsageShaderWrite;
    texdesc.pixelFormat = dstTexture.pixelFormat;
    _outTexture = [_device newTextureWithDescriptor:texdesc];
  

  }

  id <MTLCommandBuffer> upscaleCommandBuffer = [_commandQueue commandBuffer]; upscaleCommandBuffer.label = @"Upscale Command Buffer";

  _mfxSpatialScaler.colorTexture = srcTexture; _mfxSpatialScaler.outputTexture = _outTexture; [_mfxSpatialScaler encodeToCommandBuffer:upscaleCommandBuffer];

  // outTexture = _outTexture; id <MTLCommandBuffer> textureCommandBuffer = [_commandQueue commandBuffer]; id <MTLBlitCommandEncoder> _mfxSpatialEncoder =[textureCommandBuffer blitCommandEncoder];

  [_mfxSpatialEncoder copyFromTexture:_outTexture toTexture:outTexture]; [_mfxSpatialEncoder endEncoding]; [upscaleCommandBuffer commit];

}

@end

extern "C" { void MetalFX_SpatialScaling(void* srcTexturePtr, void* dstTexturePtr, void* outTexturePtr) {

    if (delegateObject == nil) {
        if (@available(iOS 16.0, *)) {
            delegateObject = [[MetalFXDelegate alloc] init];
        } else {
            // Fallback on earlier versions
        }
    }
    
    if (srcTexturePtr == nil || dstTexturePtr == nil || outTexturePtr == nil) {
        return;
    }
    
    id<MTLTexture> srcTexture = (__bridge id<MTLTexture>)(void *)srcTexturePtr;
    id<MTLTexture> dstTexture = (__bridge id<MTLTexture>)(void *)dstTexturePtr;
	id<MTLTexture> outTexture = (__bridge id<MTLTexture>)(void *)outTexturePtr;

    if (@available(iOS 16.0, *)) {
        [delegateObject SpatialScaling: srcTexture
                            dstTexture: dstTexture
							outTexture: outTexture];
    } else {
        // Fallback on earlier versions
    }
     return;
}

}

With the C# and objective code, the appear on screen is black. If I save the MTLTexture to PNG in ios plug in, the PNG is ok(not black), so I think the outTexture: outTexture write to unity is failed.