Cubic line charts don't get filled correctly if data doesn't start at index 0

[gunterhager]

If you set up your data entries for the cubic line chart so that they don't start at x-index 0, the fill is still drawn from x-index 0.

Set up data entries like this:

[[ChartDataEntry alloc] initWithValue:val xIndex:i + offset]

The chart will look like this:

This happens only with cubic line charts. Regular line charts are rendered like this:

You can easily reproduce the bug by replacing the setDataCount:range: method in CubicLineChartViewController.m in the demo with:

- (void)setDataCount:(int)count range:(double)range
{
    NSMutableArray *xVals = [[NSMutableArray alloc] init];

    for (int i = 0; i < count; i++)
    {
        [xVals addObject:[@(i + 1990) stringValue]];
    }

    NSMutableArray *yVals1 = [[NSMutableArray alloc] init];

    int offset = 10;

    for (int i = 0; i < count - offset; i++)
    {
        double mult = (range + 1);
        double val = (double) (arc4random_uniform(mult)) + 20;
        [yVals1 addObject:[[ChartDataEntry alloc] initWithValue:val xIndex:i + offset]];
    }

    LineChartDataSet *set1 = [[LineChartDataSet alloc] initWithYVals:yVals1 label:@"DataSet 1"];
    set1.drawCubicEnabled = YES;
    set1.cubicIntensity = 0.2;
    set1.drawCirclesEnabled = NO;
    set1.lineWidth = 1.8;
    set1.circleRadius = 4.0;
    [set1 setCircleColor:UIColor.whiteColor];
    set1.highlightColor = [UIColor colorWithRed:244/255.f green:117/255.f blue:117/255.f alpha:1.f];
    [set1 setColor:UIColor.whiteColor];
    set1.fillColor = UIColor.whiteColor;
    set1.fillAlpha = 0.5f;
    set1.drawFilledEnabled = YES;
    set1.drawHorizontalHighlightIndicatorEnabled = NO;
    set1.fillFormatter = [[CubicLineSampleFillFormatter alloc] init];

    LineChartData *data = [[LineChartData alloc] initWithXVals:xVals dataSet:set1];
    [data setValueFont:[UIFont fontWithName:@"HelveticaNeue-Light" size:9.f]];
    [data setDrawValues:NO];

    _chartView.data = data;
}