C# Font Scaling

In certain scenarios, it’s not always possible to determine beforehand the exact dimensions required to display a string. In these cases, you might want to scale the font so that the text fits neatly within a given space, such as a panel or a window.

We will write a function that takes in the following parameters:

public static Font AppropriateFont(Graphics g, float minFontSize, 
    float maxFontSize, Size layoutSize, string s, Font f, out SizeF extent)

For example, here is the implementation of the AppropriateFont function:

public static Font AppropriateFont(Graphics g, float minFontSize, 
    float maxFontSize, Size layoutSize, string s, Font f, out SizeF extent)
{
    // If min and max font sizes are the same, use the specified font size
    if (maxFontSize == minFontSize)
        f = new Font(f.FontFamily, minFontSize, f.Style);

    // Measure the string with the current font
    extent = g.MeasureString(s, f);

    // If max font size is less than or equal to min font size, return the current font
    if (maxFontSize <= minFontSize)
        return f;

    // Calculate the ratios between the available layout size and the string size
    float hRatio = layoutSize.Height / extent.Height;
    float wRatio = layoutSize.Width / extent.Width;
    float ratio = Math.Min(hRatio, wRatio);

    // Calculate the new font size based on the ratio
    float newSize = f.Size * ratio;

    // Ensure the new font size is within the specified bounds
    if (newSize < minFontSize)
        newSize = minFontSize;
    else if (newSize > maxFontSize)
        newSize = maxFontSize;

    // Create the new font with the calculated size
    f = new Font(f.FontFamily, newSize, f.Style);

    // Measure the string again with the new font
    extent = g.MeasureString(s, f);

    return f;
}

We first check if the minFontSize and maxFontSize are the same. If they are, we directly create a new font with the minFontSize and return it immediately.

Next, we measure the initial dimensions of the string with the specified font using the Graphics.MeasureString method.

We will calculate the available space ratio by comparing the layout size with the current string dimensions. The ratio is calculated for both height and width, and the smaller of the two ratios is chosen. This ensures that the font scales in proportion to both dimensions without distorting the string.

We multiply the current font size by the ratio to get the new font size that should fit within the layout. If the new font size falls outside the minFontSize and maxFontSize bounds, we constrain it to stay within those limits.

After adjusting the font size, we create a new font with the calculated size, measure the string again with the new font, and return the font.

To demonstrate how to use the AppropriateFont function, here is a simple Windows Forms application that resizes text dynamically to fit within the form's client area:

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

namespace FontScaling
{
    public partial class Form1 : Form
    {
        string _text = "Resize Me!!";

        public Form1()
        {
            InitializeComponent();
            this.SetStyle(ControlStyles.ResizeRedraw, true);
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            using (Font f = new Font("Tahoma", 15))
            {
                SizeF size;
                using (Font f2 = AppropriateFont(e.Graphics, 5, 50, 
                        ClientRectangle.Size, _text, f, out size))
                {
                    PointF p = new PointF(
                        (ClientRectangle.Width - size.Width) / 2, 
                        (ClientRectangle.Height - size.Height) / 2);
                    e.Graphics.DrawString(_text, f2, Brushes.Black, p);
                }
            }

            base.OnPaint(e);
        }

        public static Font AppropriateFont(Graphics g, float minFontSize, 
            float maxFontSize, Size layoutSize, string s, Font f, out SizeF extent)
        {
            // Method implementation here...
        }
    }
}

In this example:

• The form's OnPaint method calls the AppropriateFont function, passing in the current client size as the layout for the text.
• The text is drawn in the center of the form, using the font returned by AppropriateFont, which is scaled to fit within the available space.