UI Toolkit slider fill has gaps in certain positions when a style with rounded corners is applied to it

6.7.X

Won't Fix

Hi, and thanks for the detailed report and the sample project. The clear repro made this much easier to investigate. After looking into it, we've decided to close this as "Won't Fix," and I'd like to explain the reasoning rather than leave it at that. The slider's fill is meant to line up with the handle so there's no gap between them, so the fill is drawn to the center of the handle. The handle always stays inside the track and never slides past the ends, which means at the lowest value its center is already slightly in from the edge. That creates a trade-off where only two of these three things can be true at once: the fill meets the handle with no gap, the fill is completely empty at the minimum value, the fill completely covers the track at the maximum value. We tried each option. Making the fill exactly empty and full at the ends brings back a visible gap next to the handle, or makes the fill poke slightly past it, which looks worse and is the same kind of gap this report is about. The only way to get all three is to let the handle hang halfway off the ends of the track, and that would change how the handle looks and how dragging feels across every slider and scrollbar in the Editor. That is too broad and risky a change for what is a cosmetic effect in a heavily customized style. The effect only shows up when the fill is given a large corner radius, as in your sample; the standard slider is not affected. If you would like a rounded fill that always sits flush against the handle, the most dependable options today are to use a smaller corner radius on the fill so the rounding is less pronounced, or to build a small custom control for that exact look. Thanks again for the report and the time you put into it. It genuinely helped us weigh the options, even though we are leaving the current behavior in place.