Added area diagram functionality

[hackingotter]

Hello

I like JBchartView, but I missed the possibility to fill the area under the lines to create a area diagram so I added it. I also added the area diagram to the sample.

I tried to follow the code style of the rest of the porject.

[simonbromberg]

This would be a great addition.

[hackingotter]

Now it works with the smoothed curves of Version 2.4.0

[simonbromberg]

Wobble issue for linear lines still seems to affect the bottom of a section

[hackingotter]

I forgot to change the slope calculation for the bottom line. Now it works.

[hackingotter]

@terryworona Is there any particular reason, why this pull reequest hasn't been merged so far? I'm just wondering why it didn't happen until now.

[terryworona]

@hackingotter been meaning to look it over. This weekend! Promise!

[hackingotter]

great. Thank you

[terryworona]

Why are these IBOutlets (forgive my naiveness, I never use IB); can the chart not be used with IB without these declared as outlets?

[hackingotter]

the IBOutlets make it possible to set the delegate and the dataSource directly in IB, like it's possible for standard UI elements like UITextField. It's just for convinience, the charts can be used without the IBOutlets, too.

[terryworona]

Looked over the request. Generally looks good, but not quite ready for prime-time yet.

There's a bunch of duplicate code that I think can be condensed. As well, I'd like to simply the interface for filling in lines.

What do you think?

[hackingotter]

I will try to remove the duplicate code. This will also improve the intergrationof future improvements.

A simpler interface also would be nice. I'll use a delegate methode for the filling and for the filling color I will use the line color and lower the alpha so you still can seperate between line and the filling.

About the stacked/cumulative lines I think that this feature should be left as it is, as I mentioned above.
It also solves the problem with the filling if two lines intersect each other.

[hackingotter]

Ok, I changed a lot and condensed most of the duplicates but at one point there still is one (marked with FIXME) I don't know how to remove.

For details loock at the comments I made.

[skywinder]

Yay! It's very cool feature! Thanks!

[hackingotter]

@terryworona Could you please review the changes I made?

[terryworona]

Hey @hackingotter, thanks so much for the contribution and continued work on getting this polished.

After a bit of discussion, we have decided to not pull in this particular feature, for a few reasons:

1. It's a rather large chunk of code -- not saying this is a bad thing, it's just that we prefer smaller, more manageable contributions (we are quite busy with our own work, and currently don't have the bandwidth to support large (untested) feature additions).
2. We have been working on our own implementation of area graphs; it will be a new subclass of JBChartView and contain a similar interface to JBLineChartView.
3. After running the branch through it's paces, it does still have some issues related to padding. Rather than make you fix these, re-test and potentially not pull it in, we would rather be honest.

Your contributions are not at all lost and will be used going forward with our area graphs. You will be given contributor credit via the PR when the time comes.

Thanks again!

[skywinder]

But a little improvement with IBOutlet is good feature to support storyboards:
+@property (nonatomic, weak) IBOutlet id<JBBarChartViewDelegate> delegate;