Slider thumb "compensation" for the positioning results in poor UX when dragging

[tiborgg]

Hi. I noticed that when starting to drag the slider thumb, the mouse cursor never remains in the same position relative to the thumb as to when the drag was started, but rather it always follows the range. I understand why this is happening, because you're trying to compensate for the thumb width within the range.

To test this out you can simply go the Slider component page on the site, move the thumb all the way to the left, and then start dragging by clicking the thumb on it's right. You will see that after the first movement the thumb will jump, since the slider actually registers that movement at 10px from the left of the range, rather than looking at the delta of the movement.

I think we should have the option of disabling this mechanism, since it's especially annoying for non circular thumbs, or thumbs which simply have their center match the range extremity (allowing the thumb to occupy space outside of the range).

Also I think the dragging mechanism should take into consideration the position within the thumb on which the drag was started, and never deviate from that. Or in other words, just look at the delta of the movement, rather than the absolute position within the range.