Viewport implementation

[philjay]

Viewport implementation

[PhilJay]

So your problem is that you can set the scale minimum so that the user cannot fully zoom out the x-axis, but the starting position is not correct / cannot be changed?

[Praveen2106]

Yes. Exactly. Since it is a timeline chart, I would like to start from last which will be latest entry.

[PhilJay]

Very well. Thankfully, that does not look like that a major issue to me.

I am going to look into that problem within the next hours and will hopefully be able to push a quick fix alongside with some other changes until tomorrow night (Europe), at the latest.

[Praveen2106]

Thanks Phil.

[PhilJay]

I have now implemented this feature in my local commit. The only problem for me is that I don't think it's good enough yet :-)

I will try to change the implementation to a way that is satisfying for me within the next few hours to push on master or push the features current implementation to the experimental banch.

[PhilJay]

Allright, the implementation is now complete and pushed to master.
You can see an example in the ExampleProject inside the LineChartActivity.

The basic functionality is as follows.

The new method centerViewPort(int xIndex, float val) makes it possible to aim the center of the view to a specific position inside the chart, described by the index on the x-axis and the value on the y-axis. This also works very well in combination with the setScaleMinima(...) method.

Example:
A chart containing 50 entries ranging from 0-1000 with their values.

Chart.setData(...);

// restrain x-axis
Chart.setScaleMinima(3f, 1f);

// center view to index 50 and value 500
Chart.centerViewPort(50, 500f);
//.. now view is positioned on the right side of the chart on the x-axis and centered on the y-axis

[Praveen2106]

Thanks Phil. I'm going to test it right away !!

[PhilJay]

Allright. Please let me know if it works and if you are having any problems.

[Praveen2106]

Sorry. It took time to get back. centerViewPort works fine. But i have to click somewhere on the Chart to make it work. Tried invalidating the chart after calling centerViewPort. But still doesn't work.

    mChart.setData(data);
    mChart.invalidate();

    mChart.centerViewPort(11, 92);
    mChart.invalidate();

[PhilJay]

Thank you for your response.
Indeed, there still was a minor issue in the implementation of the centerViewPort(...) method that caused the problem you described.
I managed to track down the bug and fix it.

It should now work as expected.

Just for the record, this is the correct implementation (you can also find it in the example project):

// first, set data
mChart.setData(...);

// restrain the maximum zoomout level, e.g.
mChart.setScaleMinima(3f, 3f);

// center the "camera" to your desired position
mChart.centerViewPort(xIndex, value);

// there should be no further need for calling invalidate()

[Praveen2106]

It works fine now !! Thanks.

[wenli135]

Still met this problem with the latest release, the chart show correctly only after touch it