Writing to RenderTexture in a compute shader doesn't work on Metal

Hi,
I'm writing to RWTexture2D<float4> texture in a compute shader. It's working nicely on desktop with directx. But it doesn't work on metal with iphone or ipad.

I have tried it on 2017.4.4 and newest beta 2018.2b9 too.

Compute Shader

Code (CSharp):

1. RWTexture2D<float4> textureOut;
2. StructuredBuffer<float4> colors;
3.  
4. #pragma kernel pixelCalc  
5.  
6. [numthreads(16,16,1)]        
7. void pixelCalc (uint2 id : SV_DispatchThreadID){
8.      textureOut[id.xy] = colors[id.x + id.y * 250];
9. }

CPU side:

Code (CSharp):

1. this.outputTexture = new RenderTexture(250, 250, 32);
2.             this.outputTexture.enableRandomWrite = true;
3.             this.outputTexture.useMipMap = false;
4.             this.outputTexture.Create();
5.  
6. this.colorArray = new Color[250 * 250];
7.  
8. // Color size is four values of four bytes, so 4 * 4
9.             this.colorsBuffer = new ComputeBuffer(this.colorArray.Length, 4 * 4);
10.  
11.             // again, we're setting color array to the buffer
12.             colorsBuffer.SetData(colorArray);
13.  
14.  
15.             var overlayGameObject = GameObject.Find("Overlay");
16.             var renderer = overlayGameObject.GetComponent<Renderer>();
17.             renderer.material.mainTexture = this.outputTexture;
18.  
19. ar kernelIndex = this.shader.FindKernel("pixelCalc");
20.  
21.             this.shader.SetBuffer(kernelIndex, "colors", colorsBuffer);
22.             this.shader.SetTexture(kernelIndex, "textureOut", this.outputTexture);
23.  
24.             this.shader.Dispatch(kernelIndex, 16, 16, 1);

Am I doing something wrong or render texture simply doesn't work in metal and compute shaders?

P.S.: I have tried an approach used here. But without success:
https://forum.unity.com/threads/con...ass-shader-to-unity-hlsl.418238/#post-3478159

Basically passing StructuredBuffer in normal shader. And bypassing usage of render texture.
Thanks
Peter

 

I'd guess its something you are doing wrong, because I've had this sort of thing working consistently on metal for macOS for a very long time with a very large number of different Unity versions, including all the 2018.2 betas. I've had the same stuff working on iOS too, but I dont test that so often.

I'm not in a position to work out exactly what is wrong with your code, but there is some very low hanging fruit that I would probably explore first if it were me:

The third parameter you are setting when doing new rendertexture is the number of bits in depth buffer, you are using a value of 32 but the manual only mentions 0,16,24 as valid settings.

Try setting a RenderTextureFormat explicitly (4th parameter when creating new rendertexture.)

Try power of 2 texture resolutions (eg 256x256 rather than 250x250)

Rule out the StructuredBuffer side of your code/Unity as potentially being the problem, by trying some code that reads from another texture rather than a buffer.

Try different numthreads values (and associated dispatch parameters).

 

Thanks you guys for your recommendations. So far I have tried to set rendercamera depth to 16 (will try 24 as next)
Changed code to use 256x256 to mach threads total.

I have removed StructuredBuffer part of compute shader and CPu code.
So it looks like this now:

Code (CSharp):

1. RWTexture2D<float4> textureOut;
2. //StructuredBuffer<float4> colors;
3.  
4. #pragma kernel pixelCalc
5.  
6. [numthreads(16,16,1)]                            
7. void pixelCalc (uint2 id : SV_DispatchThreadID){
8.     textureOut[id.xy] = float4(1, 0, 0, 1);//colors[id.x + id.y * 256];
9. }

Code (CSharp):

1. this.outputTexture = new RenderTexture(256, 256, 16);
2.             this.outputTexture.enableRandomWrite = true;
3.             this.outputTexture.Create();
4.  
5. var kernelIndex = this.shader.FindKernel("pixelCalc");
6.  
7.             //this.shader.SetBuffer(kernelIndex, "colors", colorsBuffer);
8.             this.shader.SetTexture(kernelIndex, "textureOut", this.outputTexture);
9.  
10.             this.shader.Dispatch(kernelIndex, 16, 16, 1);

But still without sucess. On Desktop I get red screen as background on ipad nothing. Just my objects so it doesn't crashed or whatever.

So what is left:
Try setting a RenderTextureFormat explicitly
And 24 depth for render texture. I will try that next.

Maybe it would be great to have an ios sample project that is working for sure.
Thanks
Peter

 

Wow, now it finally works at least with some settings.

I have used this:

Code (CSharp):

1. RWTexture2D<float4> textureOut;
2. StructuredBuffer<float4> colors;
3.  
4. #pragma kernel pixelCalc
5.  
6. [numthreads(8,8,1)]                            
7. void pixelCalc (uint2 id : SV_DispatchThreadID){  
8.     textureOut[id.xy] = colors[id.x + id.y * 256];
9. }

Code (CSharp):

1. this.outputTexture = new RenderTexture(256, 256, 24);
2.             this.outputTexture.enableRandomWrite = true;
3.             this.outputTexture.Create();
4.          
5.  
6. var kernelIndex = this.shader.FindKernel("pixelCalc");
7.  
8.             this.shader.SetBuffer(kernelIndex, "colors", colorsBuffer);
9.             this.shader.SetTexture(kernelIndex, "textureOut", this.outputTexture);
10.  
11.             this.shader.Dispatch(kernelIndex, 256 / 8, 256 / 8, 1);

Decision point was lowering threads to 8 8 1. I will experiment with it further but it looks like it's not working with 16 16 1.

But at least it's working with structured buffer and render rexture

Thanks!

 

I'm testing it on iPhone SE and iPad 2018. iOS version 11.4

Of course I will try to set back again bigger number of threads as I was tweaking many values and I could make an mistake. Although I doubt. (I was checking threads limit too in specifications and 256 seemed to be safe for all devices)

Sadly I'm not using metal validation. I'm experimenting now with windows only development machine. So I'm developing it on windows 10 and for building I'm using Unity Cloud. (As far I see this option is available only in metal editor)

Developing on windows is very comfortable for me. Although it has its drawbacks as you see...

Peter