Scrollbar ticks show up under thumb on Mac with Lion scrollbars, with trackpad

[njx]

1. On Mac, do a Find in the current document
2. Touch-scroll

Result: The thumb shows up above the tickmarks on the right. If you mouse over the thumb to drag it, the track is nearly opaque and makes it nearly impossible to see the tickmarks.

[peterflynn]

Note: doesn't repro if you have a mouse plugged in (or scrollbars set to always-on even with touchpad). Only the touch/iOS-style scrollbars will show the bug.

[peterflynn]

@njx Looks like this is a fact of life on Mac: http://jsfiddle.net/N5r38/1/. Lion scrollbars paint on top of everything else in the window, regardless of z-ordering. (Clearly this example isn't doing exactly what CM does, since for some reason this simple code fails to get the scrollbar to expand when dragged / moused over... but I did verify in Brackets that that tickmarks are indeed z-ordered above the scrolling region -- so it's still the same issue).

Interestingly, this Firefox bug seems to suggest that the behavior used to be different (respecting normal z-ordering, like on Windows) in both FF and Chrome. Not sure when it might have changed.

The only workarounds I've seen suggested are to use custom scrollbar CSS, which I'm sure drops down to custom rendering code in the browser's own rendering pipline, respecting the z-ordering more normally. But obviously that has lots of disadvantages...

[njx]

To @peterflynn, low pri to consider whether there's another design tweak we could do that would help.

[peterflynn]

In particular, we talked about either:

• Making the tickmarks wider so they stick out past the edge of the scrollbar, or
• Shifting the tickmarks over so they are next to the scrollbar rather than overlapping it

In either case we'd ideally only do this on Mac when scrollbars aren't always-visible -- I think CM has a heuristic for detecting this which we could probably piggy-back on.

[TomMalbran]

If we added custom scrollbars for mac too, would it fix this?

[njx]

Potentially, but I don't think we want to go that route just for this bug - trying to simulate native behavior exactly is tricky.

[peterflynn]

Exactly -- the Mac native scrollbars are significantly more nuanced than the other platforms. It would definitely fix this, but I agree with NJ that we shouldn't do that.