Unreal engine c++ write delegate OnScreenshotCaptured - c++

Question

I am new to C++. I've wrote code in C# and PHP.Since I am using Unreal engine I am trying to learn C++. For my project I need to make a screenshot in-game and show it immediately so I want to get it as a texture.
I made a blueprint node which calls this function i've made:
void UMyBlueprintFunctionLibrary::TakeScreenshot()
{
FScreenshotRequest::RequestScreenshot(true);
if (GEngine)
GEngine->AddOnScreenDebugMessage(-1, 15.0f, FColor::Red, "Tried to take screenshot");
}
When I hover my mouse above RequestScreenshot I see the following pop-up:
"Screenshot can be read from memory by subscribing to the viewsport OnScreenshopCaptured delegate"
So that is what I try to do but I have no idea how I looked up this:
https://docs.unrealengine.com/latest/INT/API/Runtime/Engine/Engine/UGameViewportClient/OnScreenshotCaptured/
Can someone tell me how to implement this and how you see/know how to implement it?

Answer 1

I have an alternative, no delegate, but FRenderTarget::ReadPixel() to some buffer you allocated, by implementing your own UGameViewportClient (inherit it), and overriding Draw() function.
I'll show the essential codes, but not complete.
void UMyGameViewportClient::Draw(FViewport* Viewport, FCanvas* SceneCanvas)
{
Super::Draw(Viewport, SceneCanvas);
if (any_condition_you_need) {
CaptureFrame();
}
}
void UMyGameViewportClient::CaptureFrame()
{
if (!Viewport) {
return;
}
if (ViewportSize.X == 0 || ViewportSize.Y == 0) {
return;
}
ColorBuffer.Empty(); // Declare this in header as TArray<FColor>
if (!Viewport->ReadPixels(ColorBuffer, FReadSurfaceDataFlags(),
FIntRect(0, 0, ViewportSize.X, ViewportSize.Y)))
{
return;
}
SaveThumbnailImage();
}
void UMyGameViewportClient::SaveThumbnailImage()
{
IImageWrapperModule& wrappermodule = FModuleManager::LoadModuleChecked<IImageWrapperModule>(FName("ImageWrapper"));
auto wrapper_ptr = wrappermodule.CreateImageWrapper(EImageFormat::PNG);
for (int i = 0; i < ColorBuffer.Num(); i++)
{
auto ptr = &ColorBuffer[i];
auto r = ptr->R;
auto b = ptr->B;
ptr->R = b;
ptr->B = r;
ptr->A = 255;
} // not necessary, if you like bgra, just change the following function argument to ERGBFormat::BGRA
wrapper_ptr->SetRaw(&ColorBuffer[0], ColorBuffer.Num() * 4,
ViewportSize.X, ViewportSize.Y, ERGBFormat::RGBA, 8);
FFileHelper::SaveArrayToFile(wrapper_ptr->GetCompressed(), *ThumbnailFile);
}