Question Getting a render texture byte[] using AsyncGPUReadback.Request

Converting a camera render to a byte array using a render texture is very slow.
I've tried comparing this to the new AsyncGPUReadback.Request method, but the results I'm getting are 5x-10x slower, as can be seen in the attached project (Unity 2019.2.9f1)

What am I missing?

Thanks

 

Here is the relevant code:

public RenderTexture colorRenderTexture;
Texture2D colorTexture;
byte[] colorBytes;

public Camera topCamera;

float startTime;

public bool useAsync;

IEnumerator Start()
{

colorTexture = new Texture2D(640, 480, TextureFormat.ARGB32, false);

while (true)
{
yield return new WaitForSeconds(1);
yield return new WaitForEndOfFrame();


if(useAsync)
{

RenderTexture rt = RenderTexture.GetTemporary(Screen.width, Screen.height, 0, RenderTextureFormat.ARGB32);
topCamera.targetTexture = rt;
topCamera.Render();
Stopwatch_Start("With Async: ");
AsyncGPUReadback.Request(rt, 0, TextureFormat.ARGB32, OnCompleteReadback);
topCamera.targetTexture = null;
RenderTexture.ReleaseTemporary(rt);
}
else
{
Stopwatch_Start("Without Async: ");
RenderTexture.active = colorRenderTexture;
colorTexture.ReadPixels(new Rect(0, 0, 640, 480), 0, 0);
colorTexture.Apply();
Stopwatch_Stop("", true);
}
}
}

void OnCompleteReadback(AsyncGPUReadbackRequest request)
{
if (request.hasError)
{
UnityEngine.Debug.Log("GPU readback error detected.");
return;
}

var tex = new Texture2D(Screen.width, Screen.height, TextureFormat.ARGB32, false);
tex.LoadRawTextureData(request.GetData<uint>());
tex.Apply();
Stopwatch_Stop("", true);

Destroy(tex);
}

 

i didn't look in your project, but if you were to check the profiler, most probably the frame drop is coming from .Render function
So instead of double rendering, you could wait for a frame and then make the copying