GridPainter.cs

// Copyright (c) 2012-2026 The Hello World Writer (https://www.thehelloworldwriter.com).
// Licensed under the MIT License. See the LICENSE file in the project root for more information.

namespace GridlyDots
{
    using System;
    using System.Drawing;
    using System.Drawing.Drawing2D;

    /// <summary>Draws a grid on a surface.</summary>
    public class GridPainter
    {
        /// <summary>Indicates whether the grid properties have been changed.</summary>
        private bool gridChanged = true;

        /// <summary>The texture brush used to draw the grid.</summary>
        private Brush gridBrush = null!;

        /// <summary>The size of the grid dot, in pixels.</summary>
        private int dotSize = 5;

        /// <summary>The spacing between grid dots, in pixels.</summary>
        private int dotSpacing = 15;

        /// <summary>The color of the grid dots.</summary>
        private Color dotColor = Color.Red;

        /// <summary>Gets or sets the size of the grid dot, in pixels.</summary>
        public int DotSize
        {
            get
            {
                return this.dotSize;
            }

            set
            {
                this.dotSize = value;
                this.gridChanged = true;
            }
        }

        /// <summary>Gets or sets the spacing between grid dots, in pixels.</summary>
        public int DotSpacing
        {
            get
            {
                return this.dotSpacing;
            }

            set
            {
                this.dotSpacing = value;
                this.gridChanged = true;
            }
        }

        /// <summary>Gets or sets the color of the grid dots.</summary>
        public Color DotColor
        {
            get
            {
                return this.dotColor;
            }

            set
            {
                this.dotColor = value;
                this.gridChanged = true;
            }
        }

        /// <summary>
        /// Draws the grid on the specified drawing surface.
        /// </summary>
        /// <param name="graphics">The drawing surface where to draw the grid.</param>
        /// <param name="area">The area where to draw the grid.</param>
        public void Draw(Graphics graphics, Rectangle area)
        {
            ArgumentNullException.ThrowIfNull(graphics);

            // If the grid properties changed, remake the grid brush
            if (this.gridChanged || (this.gridBrush == null))
            {
                if (this.gridBrush != null)
                {
                    this.gridBrush.Dispose();
                    this.gridBrush = null!;
                }

                this.gridBrush = this.MakeGridBrush();
            }

            // Fill the area with the grid
            graphics.FillRectangle(this.gridBrush, area);
        }

        /// <summary>
        /// Creates and returns the grid texture brush, based on the current grid properties.
        /// </summary>
        /// <returns>The texture brush that will be used to fill the grid.</returns>
        private TextureBrush MakeGridBrush()
        {
            // The width and height of the grid texture bitmap (dot size + dot space)
            int size = this.DotSize + this.DotSpacing;

            // Create and fill the grid texture bitmap
            using Bitmap bitmap = new(size, size);
            using (Graphics graphics = Graphics.FromImage(bitmap))
            {
                using Brush dotBrush = new SolidBrush(this.DotColor);
                // Set high quality rendering for smaller dots
                graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;

                // Draw the pixel as a round circle
                graphics.FillEllipse(dotBrush, 0, 0, this.DotSize, this.DotSize);
            }

            // Return the grid texture brush
            return new TextureBrush(bitmap);
        }
    }
}