We saw this post some weeks ago and we decided to backport 5.8 changes to enable dynamic resolution on PC on 5.6:
[Content removed]
We noticed that if we want to use the Upper Bound HZB reallocation optimization without issues we need to port more changesets than the ones reported in the post.
We have ported the following changesets:
CL 48870621 Enable Dynamic Resolution support for PC RHIs DX12 and Vulkan
CL 48822173 Keep HZB texture resolution at the Upper Bound views size (View.UpperBoundViewRect) in order to avoid the RT reallocation when dynamic resolution is enabled
CL 48868636 Add missing View.UpperBoundViewRect initialization in case of r.Test.ViewRectOffset 1 and CustomRenderPasses
CL 48964853 Missing TopLeftShift correction for UpperBoundViewRect when preparing the View
I think you might need 53528049 and 53545738 as well. Even with those it seems your finding is a legitimate problem, and will need a fix, without testing but looking at the code I think with this version that keep the size should work:
for (int32 i = 0; i < Views.Num(); i++)
{
Views[i].ViewRect -= TopLeftShift;
Views[i].UpperBoundViewRect = FIntRect(Views[i].ViewRect.Min, Views[i].ViewRect.Min + Views[i].UpperBoundViewRect.Size());
}
If that works for your case of cameras with constrain aspect ratios (black borders), I will submit it for a 5.8.4 patch. Proper resizing would be in 5.9/6.0.