Translucent circular Control with text

Question

I am working on a project wherein I need to add a Control with the shape of a Circle with some text in the middle.
My problem is the circle is too small, when I resize it, it overlaps other controls. I want to draw the circle same width as the square.
Otherwise. how can I make the Control's background transparent?

I am using the code below:

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

    using (Bitmap bitmap = new Bitmap(this.Width, this.Height))
    {
        using (Graphics graphics = Graphics.FromImage(bitmap))
        {
            graphics.SmoothingMode = SmoothingMode.HighQuality;
            graphics.Clear(this.BackColor);

            using (SolidBrush brush = new SolidBrush(this._FillColor))
            {                      
                graphics.FillEllipse(brush, 0x18 - 6, 0x18 - 6, (this.Width - 0x30) + 12, (this.Height - 0x30) + 12);
            }

            Brush FontColor = new SolidBrush(this.ForeColor);
            SizeF MS = graphics.MeasureString(Convert.ToString(Convert.ToInt32((100 / _Maximum) * _Value)), Font);
            graphics.DrawString(Convert.ToString(Convert.ToInt32((100 / _Maximum) * _Value)), Font, FontColor, Convert.ToInt32((Width / 2 - MS.Width / 2) + 2), Convert.ToInt32((Height / 2 - MS.Height / 2) + 3));
            bitmap.MakeTransparent(this.BackColor);
            e.Graphics.DrawImage(bitmap, 0, 0);

            graphics.Dispose();
            bitmap.Dispose();
        }
    }
}

Answer 1

This is a Custom Control derived from Control, which can be made translucent.
The interface is a colored circle which can contain a couple of numbers.

The Control exposes these custom properties:

Opacity: The level of opacity of the control BackGround [0, 255]
InnerPadding: The distance between the inner rectangle, which defines the circle bounds and the control bounds.
FontPadding: The distance between the Text and the Inner rectangle.

Transparency is obtained overriding CreateParams, then setting ExStyle |= WS_EX_TRANSPARENT;

The Control.SetStyle() method is used to modify the control behavior, adding these ControlStyles:

▶ ControlStyles.Opaque: prevents the painting of a Control's BackGround, so it's not managed by the System. Combined with CreateParams to set the Control's Extended Style to WS_EX_TRANSPARENT, the Control becomes completely transparent.

▶ ControlStyles.SupportsTransparentBackColor the control accepts Alpha values for it's BackGround color. Without also setting ControlStyles.UserPaint it won't be used to simulate transparency. We're doing that ourselves with other means.

---

To see it at work, create a new Class file, substitute all the code inside with this code preserving the NameSpace and build the Project/Solution.
The new Custom Control will appear in the ToolBox. Drop it on a Form. Modify its custom properties as needed.

A visual representation of the control:

Note and disclaimer:

• This is a prototype Control, the custom Designer is missing (cannot post that here, too much code, also connected to a framework).
  As presented here, it can be used to completely overlap other Controls in a Form or other containers. Partial overlapping is not handled in this simplified implementation.
• The Font is hard-coded to Segoe UI, since this Font has a base-line that simplifies the position of the text in the middle of the circular area.
  Other Fonts have a different base-line, which requires more complex handling.
  See: TextBox with dotted lines for typing for the base math.

---

using System;
using System.ComponentModel;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Text;
using System.Globalization;
using System.Runtime.CompilerServices;
using System.Windows.Forms;

[DesignerCategory("Code")]
public class RoundCenterLabel : Label, INotifyPropertyChanged, ISupportInitialize 
{
    private const int WS_EX_TRANSPARENT = 0x00000020;
    private bool IsInitializing = false;
    private Point MouseDownLocation = Point.Empty;
    private readonly int fontPadding = 4;
    private Font m_CustomFont = null;
    private Color m_BackGroundColor;
    private int m_InnerPadding = 0;
    private int m_FontPadding = 25;
    private int m_Opacity = 128;

    public event PropertyChangedEventHandler PropertyChanged;

    public RoundCenterLabel() => InitializeComponent();

    private void InitializeComponent()
    {
        SetStyle(ControlStyles.Opaque |
                      ControlStyles.SupportsTransparentBackColor |
                      ControlStyles.ResizeRedraw, true);
        SetStyle(ControlStyles.OptimizedDoubleBuffer, false);
        m_CustomFont = new Font("Segoe UI", 50, FontStyle.Regular, GraphicsUnit.Pixel);
        BackColor = Color.LimeGreen;
        ForeColor = Color.White;
    }

    protected override CreateParams CreateParams {
        get {
            CreateParams cp = base.CreateParams;
            cp.ExStyle |= WS_EX_TRANSPARENT;
            return cp;
        }
    }

    public new Font Font
    {
        get => m_CustomFont;
        set { 
            m_CustomFont = value;
            if (IsInitializing) return;
            FontAdapter(value, DeviceDpi);
            NotifyPropertyChanged();
        }
    }

    public override string Text {
        get => base.Text;
        set { base.Text = value;
              NotifyPropertyChanged();
        }
    }

    public int InnerPadding {
        get => m_InnerPadding;
        set {
            if (IsInitializing) return;
            m_InnerPadding = ValidateRange(value, 0, ClientRectangle.Height - 10);
            NotifyPropertyChanged(); }
    }

    public int FontPadding {
        get => m_FontPadding;
        set {
            if (IsInitializing) return;
            m_FontPadding = ValidateRange(value, 0, ClientRectangle.Height - 10);
            NotifyPropertyChanged();
        }
    }

    public int Opacity {
        get => m_Opacity;
        set { m_Opacity = ValidateRange(value, 0, 255);
              UpdateBackColor(m_BackGroundColor);
              NotifyPropertyChanged();
        }
    }

    public override Color BackColor {
        get => m_BackGroundColor;
        set { UpdateBackColor(value);
              NotifyPropertyChanged();
        }
    }

    protected override void OnLayout(LayoutEventArgs e)
    {
        base.OnLayout(e);
        base.AutoSize = false;
    }

    private void NotifyPropertyChanged([CallerMemberName] string PropertyName = null)
    {
        InvalidateParent();
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(PropertyName));
    }

    protected override void OnMouseDown(MouseEventArgs e)
    {
        base.OnMouseDown(e);
        MouseDownLocation = e.Location;
    }

    protected override void OnMouseMove(MouseEventArgs e)
    {
        base.OnMouseMove(e);
        if (e.Button == MouseButtons.Left) {
            var loc = new Point(Left + (e.X - MouseDownLocation.X), Top + (e.Y - MouseDownLocation.Y));
            InvalidateParent();
            BeginInvoke(new Action(() => Location = loc));
        }
    }

    private void InvalidateParent()
    {
        Parent?.Invalidate(Bounds, true);
        Invalidate();
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        using (var format = new StringFormat(StringFormatFlags.LineLimit | StringFormatFlags.NoWrap, CultureInfo.CurrentUICulture.LCID))
        {
            format.LineAlignment = StringAlignment.Center;
            format.Alignment = StringAlignment.Center;
            e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
            e.Graphics.TextRenderingHint = TextRenderingHint.AntiAliasGridFit;

            using (var circleBrush = new SolidBrush(m_BackGroundColor))
            using (var foreBrush = new SolidBrush(ForeColor))
            {
                FontAdapter(m_CustomFont, e.Graphics.DpiY);
                RectangleF rect = InnerRectangle();
                e.Graphics.FillEllipse(circleBrush, rect);
                e.Graphics.DrawString(Text, m_CustomFont, foreBrush, rect, format);
            };
        };
    }

    public void BeginInit() => IsInitializing = true;

    public void EndInit()
    {
        IsInitializing = false;
        Font = new Font("Segoe UI", 50, FontStyle.Regular, GraphicsUnit.Pixel);
        FontPadding = m_FontPadding;
        InnerPadding = m_InnerPadding;
    }

    private RectangleF InnerRectangle()
    {
        (float Min, _) = GetMinMax(ClientRectangle.Height, ClientRectangle.Width);
        var size = new SizeF(Min - (m_InnerPadding / 2), Min - (m_InnerPadding / 2));
        var position = new PointF((ClientRectangle.Width - size.Width) / 2,
                                  (ClientRectangle.Height - size.Height) / 2);
        return new RectangleF(position, size);
    }

    private void FontAdapter(Font font, float dpi)
    {
        RectangleF rect = InnerRectangle();
        float fontSize = ValidateRange(
            (int)(rect.Height - m_FontPadding), 6, 
            (int)(rect.Height - m_FontPadding)) / (dpi / 72.0F) - fontPadding;

        m_CustomFont.Dispose();
        m_CustomFont = new Font(font.FontFamily, fontSize, font.Style, GraphicsUnit.Pixel);
    }

    private void UpdateBackColor(Color color)
    {
        m_BackGroundColor = Color.FromArgb(m_Opacity, Color.FromArgb(color.R, color.G, color.B));
        base.BackColor = m_BackGroundColor;
    }

    private int ValidateRange(int Value, int Min, int Max) 
        => Math.Max(Math.Min(Value, Max), Min); // (Value < Min) ? Min : ((Value > Max) ? Max : Value);

    private (float, float) GetMinMax(float Value1, float Value2) 
        => (Math.Min(Value1, Value2), Math.Max(Value1, Value2));
}