FirstVisibleIndex and LastVisibleIndex while zooming

[bairog]

Try setting the Labels separation to zero, e.g.

Up to 60 points it's working:

But for example for 70 points (when labels start to overlap each other) - chart itself performs labels thinning (my function Bottom_GetAxisDrawLabel is disabled here):

[Christopher]

Hello,

okay, well, another variation on an earlier technique seems to work in these circumstances, i.e.

Code: Select all

    public partial class Form1 : Form
    {
        //max visible labels
        private const Int32 maxDisplayedLabelsForBottomaAxis = 20;
        List<string> _labels = new List<string>();
        int _count;


        public Form1()
        {
            var rnd = new Random();

            InitializeComponent();

            tChart1.Zoomed += TChart1_Zoomed;
            tChart1.UndoneZoom += TChart1_UndoneZoom;
            tChart1.AfterDraw += TChart1_AfterDraw;

            _count = 4000;

            for (int i = 0; i < _count; i++)
            {
                line1.Add(i, rnd.Next(5));
                _labels.Add($"Point NoClue #{rnd.Next()}");

                if (ShouldDrawIndex(i, 0, _count))
                {
                    tChart1.Axes.Bottom.Labels.Items.Add(i, _labels[i]);
                }
            }
        }

        private void TChart1_AfterDraw(object sender, Steema.TeeChart.Drawing.Graphics3D g)
        {
            this.Text = $"Number of labels = {tChart1.Axes.Bottom.Labels.Items.Count}";
        }

        private void TChart1_UndoneZoom(object sender, EventArgs e)
        {
            tChart1.Axes.Bottom.Labels.Items.Clear();

            for (int i = 0; i < _count; i++)
            {
                if (ShouldDrawIndex(i, 0, _count))
                {
                    tChart1.Axes.Bottom.Labels.Items.Add(i, _labels[i]);
                }
            }
        }

        private bool ShouldDrawIndex(int index, int firstVisible, int lastVisible)
        {
            if ((lastVisible - firstVisible) > maxDisplayedLabelsForBottomaAxis)
            {
                var drawEvery = ((lastVisible - 1 - firstVisible) / maxDisplayedLabelsForBottomaAxis) + 1;
                return index % drawEvery == 0;
            }

            return true;
        }

        private void TChart1_Zoomed(object sender, EventArgs e)
        {
            tChart1.Axes.Bottom.Labels.Items.Clear();

            var xvalues = line1.XValues.Value.Where((x, i) => i < _count);

            var min = line1.XValues.IndexOf(xvalues.Where(x => x >= tChart1.Axes.Bottom.Minimum).First());
            var max = line1.XValues.IndexOf(xvalues.Where(x => x <= tChart1.Axes.Bottom.Maximum).Last());

            for (int i = min; i <= max; i++)
            {
                if(ShouldDrawIndex(i, min, max))
                {
                    tChart1.Axes.Bottom.Labels.Items.Add(i, _labels[i]);
                }
            }
        }
    }

[bairog]

okay, well, another variation on an earlier technique seems to work in these circumstances, i.e.

So we've finally returned to using Zoomed and UndoneZoom events Looks like it's working now, many thanks.

P. S. As I can see this code is in fact manually calculating FirstVisibleIndex and LastVisibleIndex. First time i was surprised by line:

Code: Select all

var xvalues = line1.XValues.Value.Where((x, i) => i < _count);

As I expected line1.XValues.Value to have exactly _count items.
Could you explain please, why that collection has more items despite of the fact that I've added _count points?

[Christopher]

Looks like it's working now, many thanks.

You're welcome.

Could you explain please, why that collection has more items despite of the fact that I've added _count points?

The Value field is public but is for internal use. If you are uncomfortable using it, you can use the more standard API calls:

Code: Select all

            List<double> xvalues = new List<double>();

            for (int i = 0; i < _count; i++)
            {
                xvalues.Add(line1.XValues[i]);
            }

            //var xvalues = line1.XValues.Value.Where((x, i) => i < _count);