Hi all!
I have been following this tutorial on Compute Shaders and I have created one.
After some small battles, I got it to compile and run, but the results are often “uninitialized”.
This is how I call the shader, which is a copy of the original one:
int AUShaderTestActor::TestComputeShader()
{
UE_LOG(LogTemp, Display, TEXT("**UShader** [%s] called TestComputeShader of object %s"), *FDateTime::Now().ToString() , *this->GetActorNameOrLabel());
// Create the parameters
FExampleShaderDispatchParameters Params(1, 1, 1);
Params.Input[0] = Input0;
Params.Input[1] = Input1;
UE_LOG(LogTemp, Display,TEXT("**UShader** [%s] Input: %d, %d"), *FDateTime::Now().ToString(), Input0, Input1);
// Execute the shader
int OutputVal = 0;
FExampleShaderInterface::Dispatch(
Params,
[&OutputVal](int Output)
{
UE_LOG(LogTemp, Display, TEXT("**UShader** [%s] Lambda: %d (OutputVal %d)"), *FDateTime::Now().ToString(), Output, OutputVal);
OutputVal = Output;
}
);
UE_LOG(LogTemp, Display, TEXT("**UShader** [%s] outside of lambda %d"), *FDateTime::Now().ToString(), OutputVal);
return OutputVal;
}
As you can see I have put some logging.
My BP actor calls this functions like the following (which I think is correct):
But this is what I’ve got as output:
LogTemp: Display: **UShader** [2024.09.05-16.35.58] called TestComputeShader of object BP_UShaderTestActor
LogTemp: Display: **UShader** [2024.09.05-16.35.58] Input: 10, 23
LogTemp: Display: **UShader** [2024.09.05-16.35.58] outside of lambda 0
LogTemp: Display: **UShader** [2024.09.05-16.35.58] Lambda: 33 (OutputVal 1065353216)
LogTemp: Display: **UShader** [2024.09.05-16.36.03] called TestComputeShader of object BP_UShaderTestActor
LogTemp: Display: **UShader** [2024.09.05-16.36.03] Input: 10, 23
LogTemp: Display: **UShader** [2024.09.05-16.36.03] outside of lambda 0
LogTemp: Display: **UShader** [2024.09.05-16.36.03] called TestComputeShader of object BP_UShaderTestActor
LogTemp: Display: **UShader** [2024.09.05-16.36.03] Input: 10, 23
LogTemp: Display: **UShader** [2024.09.05-16.36.03] outside of lambda 0
LogTemp: Display: **UShader** [2024.09.05-16.36.03] Lambda: 33 (OutputVal 0)
LogTemp: Display: **UShader** [2024.09.05-16.36.03] called TestComputeShader of object BP_UShaderTestActor
LogTemp: Display: **UShader** [2024.09.05-16.36.03] Input: 10, 23
LogTemp: Display: **UShader** [2024.09.05-16.36.03] outside of lambda 0
LogTemp: Display: **UShader** [2024.09.05-16.36.03] Lambda: 33 (OutputVal 0)
LogTemp: Display: **UShader** [2024.09.05-16.36.03] called TestComputeShader of object BP_UShaderTestActor
LogTemp: Display: **UShader** [2024.09.05-16.36.03] Input: 10, 23
LogTemp: Display: **UShader** [2024.09.05-16.36.03] outside of lambda 0
LogTemp: Display: **UShader** [2024.09.05-16.36.03] Lambda: 33 (OutputVal 0)
LogTemp: Display: **UShader** [2024.09.05-16.36.03] called TestComputeShader of object BP_UShaderTestActor
LogTemp: Display: **UShader** [2024.09.05-16.36.03] Input: 10, 23
LogTemp: Display: **UShader** [2024.09.05-16.36.03] outside of lambda 0
LogTemp: Display: **UShader** [2024.09.05-16.36.03] Lambda: 33 (OutputVal 0)
LogTemp: Display: **UShader** [2024.09.05-16.36.03] called TestComputeShader of object BP_UShaderTestActor
LogTemp: Display: **UShader** [2024.09.05-16.36.03] Input: 10, 23
LogTemp: Display: **UShader** [2024.09.05-16.36.03] outside of lambda 0
I don’t know why I cannot get the output outside of the lambda. Any hints?
Also, that spurious value… is it possible that the lambda is executed before OutputVal is even there?
Thank you!