Dragging tempo handles in pattern roll is glitchy

[nyanpasu64]

Decided to try helio-3.7-x64.AppImage for a bit. With a Logitech G203 1000 Hz mouse, I get tempo slider anomalies:

• I cannot drag an initial tempo point by the area of the point outside the pattern rectangle. And the tempo handle gets erased until the next full redraw, when I create a selection rectangle that covers the handle.
• When dragging tempo points vertically, it takes a lot of vertical dragging to enter tempo drag mode.
• When dragging vertically, the level barely changes, but jumps by a large distance once in a while.

With a Dell office mouse, it's easier to begin tempo drag mode, and the level changes properly if I move the mouse quickly. However, if I drag slowly, the level does stop moving even when my mouse is moving, until it jumps to catch up when I move the mouse quickly enough. (When dragging an intermediate point upwards, the distance the point jumps is exactly +0.200.)

I think the bug is that the app or UI library's code is dropping fractional mouse movements.

https://user-images.githubusercontent.com/913957/131765341-9ddb9af0-ee15-4138-9086-eab0b1ca37fc.mp4