473103 - Can't drag <scale> thumb when |max| and |increment| are set to large values

Status: NEW

(Toolkit :: UI Widgets, defect)

Description

[Justin Dolske [:Dolske]]

When using a <scale> with large values set for |max| and |increment|, you can't drag the thumb with the mouse. EG:

<xul:scale increment="10000" max="30000"/>

The culprit is nsSliderFrame::SetCurrentThumbPosition()...

723   if (aMaySnap && mContent->AttrValueIs(...) {
725     // If snap="true", then the slider may only be set to min + (increment * x).
726     // Otherwise, the slider may be set to any positive integer.
727     PRInt32 increment = GetIncrement(aScrollbar);
728     realpos = NSToCoordRound(realpos / float(increment)) * increment;
729   }

"realpos" here seems to be a pixel count. The end result is that it's diving $smallnum by $largenum, and realpos ends up being 0.

Looks like there needs to be some additional logic here. Say, converting realpos into a percentage, computing which slot that is (incorporating min, max, and increment), and then snapping to that slot.

Found this while working on the videocontrols, but it's not blocking. I thought the |increment| only affected what the arrow keys did (as |pageIncrement| does for pgup/pgdn). I don't want the snapping when dragging, so leaving the attribute at its default value avoids both problems.