Re: Good mouse tracking design for dynamic view?

FROM : Nathan Vander Wilt
DATE : Wed Jul 02 22:20:36 2008

>> So it seems I need to do more bookwork myself, but I'm wondering 
>> which
>> direction others would recommend:
>> a) Set up a single tracking area for the whole view, and perform 
>> all my own
>> hit testing every time the mouse moves.
>> b) Keep the per-item tracking areas, but perform my own testing in 
>> the edge
>> cases when active (mouse has entered but not exited) tracking areas 
>> are
>> getting reset.

>
> I vote for option A.
>
> Efficiency should not be a concern. [...]
>
> Reinventing hit testing shouldn't be much of a concern either [...]



Thanks all for your encouragement. Implementing it myself isn't a 
problem (the rest of the code is pretty geometry heavy, so it's 
certainly not foreign territory) and has already made it easier to 
implement (or at least try out) other ideas, like finding everything 
within a certain radius of the cursor rather than just under.

I just put a single tracking area across the entire view bounds (with 
the NSTrackingInVisibleRect, which I understand to make the tracking 
area's "frame" rect irrelevant anyway) and just run a linear search 
noting all items under the mouse every time it moves. I then compare 
this to a list from the previous check, and notify the items that have 
changed of an exit/entrance accordingly. I haven't tested performance 
with a ton of items, but as not a great amount of work is done I don't 
foresee any problem.

I had to do one little "hack" for when the view itself is exited, 
namely, when the whole-view tracking area is exited I need to manually 
"exit" all items. Otherwise when the final mouseMoved fired, some 
items could still be underneath the mouse and would remain "entered". 
Only really hackish in the sense that I need two functions to update 
the active items and post pseudo-events, rather than just the one.

thanks,
-natevw