Quick answer: Unreal RenderTarget2D::ResizeTarget clearing the existing content? Resize allocates new memory and discards old - blit content before resize if preservation is needed.
Mini-map texture resized for higher zoom. Map is now black; redraws on next tick.
Blit before resize
UKismetRenderingLibrary::DrawMaterialToRenderTarget(
this, NewRT, BlitMaterial);Manual content copy. Preserves between sizes.
Or maintain a master at max size
Always render to max-resolution RT; downscale for display. No resize needed.
Accept the clear
For frequently-changing content (post-process), the clear is fine. Save the preserve work for case-by-case.
“Resize is reallocate. Reallocate is discard.”
If your RT content is expensive to recreate, the blit pattern is mandatory. Plan it upfront.