C# Custom TrackBar Buffer Area

Question

I'm making a User Control to act as a TrackBar. I have a ToolboxCustomTrackbar1 which has a Min and Max as well as a SelectedMin which can be changed by the user dragging around a MinPanel in the area.

The MinPanel is drawn based on SelectedMin, which is changed with the following code:

    protected override void OnMouseMove(MouseEventArgs e)
    {
        base.OnMouseMove(e);

        if(e.Button == MouseButtons.Left)
        {
            UpdateSelectedMinFromMouse(e.X);
        }
    }

    private void UpdateSelectedMinFromMouse(float x)
    {
        var percentage = x * 100 / Width;
        var range = Max - Min;
        var rawValue = percentage * range / 100;
        var value = rawValue + Min;

        SelectedMin = (int)Math.Round(value);
    }

MinPanel is then drawn with the following code:

protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);

        e.Graphics.DrawRectangle(Pens.Black, 0, 0, Width - 1, Height - 1);

        minPanel.Location = new Point((int)GetPosition(ref selectedMin), 0);
        minPanel.Size = new Size(PanelWidth, Height/2);
        minPanel.BackColor = Color.Red;

        trackbarArea = new Rectangle(Buffer, 0, Width - Buffer * 2, Height);
        e.Graphics.FillRectangle(Brushes.LightBlue, trackbarArea);

    }

    private float GetPosition(ref int input)
    {
        var range = Max - Min;
        var value = input - Min;
        var percentage = (float)value * 100 / range;
        var position = percentage * Width / 100;

        Console.WriteLine(position);

        return position - (float)minPanel.Width / 2;
    }

---

This all works fine and draws the MinPanel wherever I click and drag on the control. However, I want to allow for a buffer area on the left and right of the control so as to draw the entire MinPanel even when it's at the left and right edges of the control.

I'm currently trying to do this with:

Rectangle trackbarArea = new Rectangle(Buffer, 0, Width - Buffer * 2, Height);

And this creates the area which I actually want to be considered the range for my TrackBar.

However, I can't seem to figure out how to have my control treat the Left edge of trackbarArea as the Min spot and the Right edge as the Max spot.

How can I allow my TrackBar to work with a Buffer on either side of it?

Answer 1

I created a ShiftOffset variable which I essentially use to offset both the Min and the Max:

private int ShiftOffset
{
    get { return shiftOffset; }
    set { shiftOffset = value; }
}
private int Min
{
    get { return min - ShiftOffset; }
    set { min = value; }
}
private int Max
{
    get { return max + ShiftOffset; }
    set { max = value; }
}

Then, everytime I set a value, I ValidateValue() using:

private void ValidateValue(ref int value)
{
    if (value < Min + ShiftOffset) value = Min + ShiftOffset;
    if (value > Max - ShiftOffset) value = Max - ShiftOffset;
}

In my User Control initialization, I set ShiftOffset = NormalizeSize(PanelWidth * 100); but I have yet to figure out what the appropriate value for ShiftOffset is in order to leave room to draw the last half of the Panels.

I'm trying to do some sort of PanelWidth * (Max - Min) / Width or some variation, but I can't quite get it.