Off-by-one with animate()d vis child with alpha filter swap stack

ID:2946130
 
Sep 27 2024, 12:55 pm
Resolved
Alpha mask position could be incorrect when the MASK_SWAP flag was used.
BYOND Version:515
Operating System:Windows 10 Pro 64-bit
Web Browser:Chrome 128.0.0.0
Applies to:Dream Seeker
Status: Resolved (515.1644)
This issue has been resolved.
Descriptive Problem Summary:

I'm using the following vis stack:

base
    relay
        render_target = "*\ref[base]_relay"
        appearance_flags = RESET_TRANSFORM | PIXEL_SCALE
    mask
        filters = filter(type="alpha",render_source="*\ref[base]_relay",flags=MASK_SWAP)


I'm getting unexpected results from the masking, where the mask is being shifted one pixel to the right when its child is animated using this approach.

This shouldn't be resulting in any kind of motion whatsoever to the mask, the bar itself should be moving.



I sent a message in the 516-alpha channel with a test case believing this to be a bug with the alpha:

https://discord.com/channels/725444629172060262/ 1225188300470353981/1289288325177413756

Instead, it appears this off-by-one issue is also present in the latest 515 stable build.
Oct 8 2024, 3:34 pm
Lummox JR resolved issue with message:
Alpha mask position could be incorrect when the MASK_SWAP flag was used.