Improve tooltip position calculation on collisions

[ixti]

Right now, when tooltip has collisions from all sides, the last gravity from the list is chosen.
It would be much better if powerTip will calculate the the most "easy" collision instead (the one which has more space for a tooltip).

[stevenbenner]

The most basic implementation of this isn't all that difficult. Just add up the total collision depth for each placement and use the tooltip position with the lowest total collision.

However, in my mind left and right collisions are worse than top or bottom collisions, because they require horizontal scrolling which is less intuitive to users. So the math would need to have some kind of modifier on x-axis collision values that gives some amount of preference to vertical collisions.

Finding the right value for that modifier is tricky.

Reference note: This may be related to issue #8.

[puzrin]

Finding the right value for that modifier is tricky.

Why tricky? You have to find minimal value for this formula:

missed area size + [infinity, if left/right direction broken]

If we don't care about exact missed place, then more simple weghting is enougth:

0 - no intersections
2 - intersection on top
1 - intersection on bottom
4,5 - intersection on the left/right. Can be swapped for LTR, or equalized if you don't care.

Then, just try to find location with minimal weight sum.

[stevenbenner]

Okay, that is a lot simpler, but I was thinking that there would be a threshold where small left/right collisions would be preferred over very large vertical collisions. Figuring out at what point a small left/right intersection would be given priority over a large top/bottom intersection was the part that I think would be "tricky".

Of course that might not be the best way to do it. Your suggestions, especially the weighting system, is a lot simpler to implement and probably make more sense. But I the kind of person who needs to play around with it to see if it feels right, so I need to just start building it.

This task is accepted and on the to-do list.

[speedplane]

I independently implemented something similar to this in issue #99, but there are some really good ideas here too. My implementation attempts to prevent collisions with the browser border (as opposed to the viewport border). Therefore, even if there is a collision, you can still scroll the tooltip into view.

That said, I think we could do even better.

I think the following are the factors that we should consider when implementing a smarter tooltip placement:

1. We want to minimize the amount of area that is not in the viewport.
2. Collision with a side of the viewport is better than colliding with a side of the browser window (i.e., it is preferable to put the tooltip in a spot that is in the scrollable area rather than off the screen).
3. Colliding vertically is better than colliding horizontally because vertical scroll is easier than horizontal.
4. Colliding on the bottom and right is more intuitive than on the top and left.

I implemented 2 and 3 in my fix, but I think 1 is probably worth adding as well. I'm not sure what the right weighting for these factors should be. I'll think about this some more, but feel free to weigh in.