Change the color of a small circle (dot) contained within the radio button to be red?

Question

How do I change the color of a small circle (dot) contained within the radio button to be red in Winform Application use VB.NET or C#?

Regard & Thanks, Dewi

Answer 1

I took the OP's VB code as a base and with a bit of MSDN help on using the PathGradientBrush came up with this derrived class for C#. The green and red buttons as seen in the image below are using my code, the two blue ones are the regular version.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing;
using System.Drawing.Drawing2D;

namespace WindowsFormsApplication1
{
    public class ColouredRadioButton : RadioButton
    {
        // Fields
        private Color m_OnColour;
        private Color m_OffColour;
        private Rectangle m_glint;
        private Rectangle m_circle;
        private PathGradientBrush m_flareBrush;
        private Pen m_outline;

        // Properties
        public Color OnColour
        {
            get
            {
                return m_OnColour;
            }
            set
            {
                if ((value == Color.White) || (value == Color.Transparent))
                    m_OnColour = Color.Empty;
                else
                    m_OnColour = value;
            }
        }
        public Color OffColour
        {
            get
            {
                return m_OffColour;
            }
            set
            {
                if ((value == Color.White) || (value == Color.Transparent))
                    m_OffColour = Color.Empty;
                else
                    m_OffColour = value;
            }
        }

        // Constructor
        public ColouredRadioButton()
        {
            // Init
            m_circle = new Rectangle(2, 5, 7, 7 /*Magic Numbers*/);
            m_glint = new Rectangle(3, 6, 4, 4  /*Magic Numbers*/);
            m_outline = new Pen(new SolidBrush(Color.Black), 1F /*Magic Numbers*/);

            // Generate Glint
            GraphicsPath Path = new GraphicsPath();
            Path.AddEllipse(m_glint);
            m_flareBrush = new PathGradientBrush(Path);
            m_flareBrush.CenterColor = Color.White;
            m_flareBrush.SurroundColors = new Color[] { Color.Transparent };
            m_flareBrush.FocusScales = new PointF(0.5F, 0.5F/*Magic Numbers*/);

            // Allows for Overlaying
            SetStyle(ControlStyles.SupportsTransparentBackColor, true);
            BackColor = Color.Transparent;
        }

        // Methods
        protected override void OnPaint(PaintEventArgs e)
        {
            // Init
            base.OnPaint(e);
            Graphics g = e.Graphics;
            g.SmoothingMode = SmoothingMode.AntiAlias;

            // Overlay Graphic
            if (this.Checked)
            {
                if (OnColour != Color.Empty)
                {
                    g.FillEllipse(new SolidBrush(OnColour), m_circle);
                    g.FillEllipse(m_flareBrush, m_glint);
                    g.DrawEllipse(m_outline, m_circle);
                }
            }
            else
            {
                if (OffColour != Color.Empty)
                {
                    g.FillEllipse(new SolidBrush(OffColour), m_circle);
                    g.FillEllipse(m_flareBrush, m_glint);
                    g.DrawEllipse(m_outline, m_circle);
                }
            }
        }
    }
}

If you're curious and want the code for the big red ball that I was using it to test out the brush features, here you go...

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing.Drawing2D;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;

            int Offset = 25;
            int BoxSize = 100;
            int GlintSize = (int)((double)BoxSize * ((double)3 / (double)4));
            Rectangle Circle = new Rectangle(Offset, Offset, BoxSize, BoxSize);
            Rectangle Glint = new Rectangle(Offset, Offset, GlintSize, GlintSize);

            //Debug
            //e.Graphics.FillRectangle(new SolidBrush(Color.Red), Circle);
            //e.Graphics.FillRectangle(new SolidBrush(Color.BlueViolet), Glint);

            //Generate Glint
            GraphicsPath P = new GraphicsPath();
            P.AddEllipse(Glint);
            PathGradientBrush FlareBrush = new PathGradientBrush(P);
            FlareBrush.CenterColor = Color.FromArgb(255, 255, 255, 255);
            Color[] colors = { Color.Transparent };
            FlareBrush.SurroundColors = colors;

            e.Graphics.FillEllipse(new SolidBrush(Color.FromArgb(255, 255, 0, 0)), Circle);
            e.Graphics.FillEllipse(FlareBrush, Glint);
            e.Graphics.DrawEllipse(new Pen(new SolidBrush(Color.Black), 1F), Circle);
        }
    }
}