Detailed Guide to Drawing Circles and Ellipses with SkiaSharp

SkiaSharp is a powerful 2D graphics library that can be used to draw various shapes. This article will provide a detailed introduction on how to use SkiaSharp to draw circles and ellipses in WinForms applications.

Environment Setup

First, you need to install SkiaSharp related packages through NuGet Package Manager:

• SkiaSharp
• SkiaSharp.Views
• SkiaSharp.Views.WindowsForms

Basic Knowledge

In SkiaSharp:

• Use SKCanvas.DrawCircle() method to draw circles
• Use SKCanvas.DrawOval() method to draw ellipses
• Use SKPaint class to set drawing styles (color, line width, etc.)

Complete Example Code

C#
using SkiaSharp;
using SkiaSharp.Views.Desktop;
using System;
using System.Windows.Forms;

namespace SkiaSharpDemo
{
    public partial class Form1 : Form
    {
        private SKControl skControl;

        public Form1()
        {
            InitializeComponent();
            InitializeSkiaSharp();
        }

        private void InitializeSkiaSharp()
        {
            // Create SKControl control
            skControl = new SKControl();
            skControl.Dock = DockStyle.Fill;
            skControl.PaintSurface += OnPaintSurface;
            this.Controls.Add(skControl);
        }

        private void OnPaintSurface(object sender, SKPaintSurfaceEventArgs e)
        {
            // Get drawing canvas
            SKCanvas canvas = e.Surface.Canvas;
            
            // Clear canvas (using white background)
            canvas.Clear(SKColors.White);

            // Create paint brush
            using (SKPaint paint = new SKPaint())
            {
                // Set basic properties
                paint.IsAntialias = true; // Enable anti-aliasing
                
                // 1. Draw solid red circle
                paint.Style = SKPaintStyle.Fill;
                paint.Color = SKColors.Red;
                canvas.DrawCircle(100, 100, 50, paint);

                // 2. Draw blue circle border
                paint.Style = SKPaintStyle.Stroke;
                paint.Color = SKColors.Blue;
                paint.StrokeWidth = 3;
                canvas.DrawCircle(250, 100, 50, paint);

                // 3. Draw gradient circle
                using (SKPaint gradientPaint = new SKPaint())
                {
                    gradientPaint.IsAntialias = true;
                    var shader = SKShader.CreateRadialGradient(
                        new SKPoint(400, 100),
                        50,
                        new SKColor[] { SKColors.Yellow, SKColors.Red },
                        null,
                        SKShaderTileMode.Clamp);
                    gradientPaint.Shader = shader;
                    canvas.DrawCircle(400, 100, 50, gradientPaint);
                }

                // 4. Draw solid green ellipse
                paint.Style = SKPaintStyle.Fill;
                paint.Color = SKColors.Green;
                paint.Shader = null;
                canvas.DrawOval(new SKRect(50, 200, 150, 300), paint);

                // 5. Draw purple ellipse border
                paint.Style = SKPaintStyle.Stroke;
                paint.Color = SKColors.Purple;
                paint.StrokeWidth = 2;
                canvas.DrawOval(new SKRect(200, 200, 300, 250), paint);

                // 6. Draw dashed ellipse
                paint.Style = SKPaintStyle.Stroke;
                paint.Color = SKColors.Orange;
                paint.StrokeWidth = 2;
                paint.PathEffect = SKPathEffect.CreateDash(new float[] { 10, 5 }, 0);
                canvas.DrawOval(new SKRect(350, 200, 450, 300), paint);
            }
        }
    }
}

Important Notes

1. Remember to dispose of SKPaint objects after use
2. The coordinate system origin (0,0) is at the top-left corner of the window
3. Use SKControl.Invalidate() method to trigger redrawing
4. Gradients and effects consume more resources, use them moderately

Summary

SkiaSharp provides flexible and powerful graphics drawing capabilities. By properly using DrawCircle and DrawOval methods, combined with various properties of SKPaint, you can draw circles and ellipses with various styles. In practical applications, you can combine these basic functions according to your needs to create more complex graphics effects.