Question

i have GRP tracks on map, which have difficulty from 1 to 10. I want these tracks to have different color depending on difficulty. Easy difficulty is green, hard is red and medium is orange. However, i need to have not just these 3 colors but smoother transitions between them. like one color for every point of difficulty or one for every half point. Is there any algorithm to compute these colors and theirs transitions? Like somehow increasing/decreasing rgb values? Thank you.

Answer 1

using System;
using System.Drawing;
using System.Windows.Forms;

public partial class MainForm : Form
{
    protected override void OnPaint(PaintEventArgs e)
    {
        Color[] colors = new Color[11];

        colors[0] = Color.Green;
        colors[1] = Interpolate(Color.Green, Color.Orange, 0.2);
        colors[2] = Interpolate(Color.Green, Color.Orange, 0.4);
        colors[3] = Interpolate(Color.Green, Color.Orange, 0.6);
        colors[4] = Interpolate(Color.Green, Color.Orange, 0.8);
        colors[5] = Color.Orange;
        colors[6] = Interpolate(Color.Orange, Color.Red, 0.2);
        colors[7] = Interpolate(Color.Orange, Color.Red, 0.4);
        colors[8] = Interpolate(Color.Orange, Color.Red, 0.6);
        colors[9] = Interpolate(Color.Orange, Color.Red, 0.8);
        colors[10] = Color.Red;

        Rectangle rect = new Rectangle(10, 10, 20, 90);
        for (int i = 0; i < colors.Length; i++)
        {
            e.Graphics.FillRectangle(new SolidBrush(colors[i]), rect);
            rect.Offset(20, 0);
        }

        base.OnPaint(e);
    }

    private static Color Interpolate(Color a, Color b, double t)
    {
        int R = (int)(a.R + (b.R - a.R) * t);
        int G = (int)(a.G + (b.G - a.G) * t);
        int B = (int)(a.B + (b.B - a.B) * t);
        return Color.FromArgb(R, G, B);
    }

    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new MainForm());
    }
}