SkiaSharp 提供了强大的图像处理能力，其中图像旋转是最常用的操作之一。本文将深入探讨SkiaSharp中图像旋转的多种方法和技巧。

Nuget 安装包

C#
SkiaSharp
SkiaSharp.Views.WindowsForms

基本旋转方法

简单角度旋转

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

namespace AppRotation
{
    public partial class Form1 : Form
    {
        private SKBitmap originalBitmap;
        private string currentImagePath;
        public Form1()
        {
            InitializeComponent();
        }

        private void btnLoad_Click(object sender, EventArgs e)
        {
            using (OpenFileDialog openFileDialog = new OpenFileDialog())
            {
                openFileDialog.Filter = "Image Files|*.png;*.jpg;*.jpeg;*.bmp;*.gif";
                if (openFileDialog.ShowDialog() == DialogResult.OK)
                {
                    currentImagePath = openFileDialog.FileName;
                    using (var fileStream = new FileStream(currentImagePath, FileMode.Open))
                    {
                        originalBitmap = SKBitmap.Decode(fileStream);
                        UpdateRotatedImage(pic, tbAngle.Value);
                        btnSave.Enabled = true;
                    }
                }
            }
        }

        private void tbAngle_Scroll(object sender, EventArgs e)
        {
            lblAngle.Text = $"Rotation Angle: {tbAngle.Value}°";
            if (originalBitmap != null)
            {
                UpdateRotatedImage(pic, tbAngle.Value);
            }
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            if (originalBitmap == null) return;

            using (SaveFileDialog saveFileDialog = new SaveFileDialog())
            {
                saveFileDialog.Filter = "PNG Image|*.png|JPEG Image|*.jpg|BMP Image|*.bmp";
                saveFileDialog.DefaultExt = "png";
                saveFileDialog.AddExtension = true;

                if (saveFileDialog.ShowDialog() == DialogResult.OK)
                {
                    using (SKBitmap rotatedBitmap = RotateImage(originalBitmap, tbAngle.Value))
                    {
                        using (SKImage image = SKImage.FromBitmap(rotatedBitmap))
                        using (SKData data = image.Encode(SKEncodedImageFormat.Png, 100))
                        using (FileStream stream = new FileStream(saveFileDialog.FileName, FileMode.Create))
                        {
                            data.SaveTo(stream);
                        }
                    }
                    MessageBox.Show("Image saved successfully!", "Success", MessageBoxButtons.OK, MessageBoxIcon.Information);
                }
            }
        }

        private void UpdateRotatedImage(PictureBox pic, int angle)
        {
            if (originalBitmap == null) return;

            using (SKBitmap rotatedBitmap = RotateImage(originalBitmap, angle))
            {
                using (SKImage image = SKImage.FromBitmap(rotatedBitmap))
                using (SKData data = image.Encode())
                using (MemoryStream memStream = new MemoryStream())
                {
                    data.SaveTo(memStream);
                    memStream.Position = 0;

                    if (pic.Image != null)
                    {
                        pic.Image.Dispose();
                    }

                    pic.Image = new Bitmap(memStream);
                }
            }
        }

        public SKBitmap RotateImage(SKBitmap originalBitmap, float angle)
        {
            // 创建一个新的位图，大小适应旋转后的图像  
            SKBitmap rotatedBitmap = new SKBitmap(
                (int)(Math.Abs(originalBitmap.Width * Math.Cos(angle * Math.PI / 180)) +
                      Math.Abs(originalBitmap.Height * Math.Sin(angle * Math.PI / 180))),
                (int)(Math.Abs(originalBitmap.Width * Math.Sin(angle * Math.PI / 180)) +
                      Math.Abs(originalBitmap.Height * Math.Cos(angle * Math.PI / 180)))
            );

            using (SKCanvas canvas = new SKCanvas(rotatedBitmap))
            {
                // Clear canvas with transparent background  
                canvas.Clear(SKColors.Transparent);

                // 将画布中心移动到图像中心  
                canvas.Translate(rotatedBitmap.Width / 2f, rotatedBitmap.Height / 2f);

                // 旋转画布  
                canvas.RotateDegrees(angle);

                // 绘制原始图像，使其居中  
                canvas.DrawBitmap(originalBitmap,
                    new SKPoint(-originalBitmap.Width / 2f, -originalBitmap.Height / 2f));
            }

            return rotatedBitmap;
        }
    }
}

保持原始尺寸的旋转

C#
public SKBitmap RotateImageInPlace(SKBitmap originalBitmap, float angle)
{
    SKBitmap rotatedBitmap = new SKBitmap(originalBitmap.Width, originalBitmap.Height);

    using (SKCanvas canvas = new SKCanvas(rotatedBitmap))
    {
        // 填充背景（可选）
        canvas.Clear(SKColors.Transparent);

        // 将画布中心移动到图像中心
        canvas.Translate(originalBitmap.Width / 2f, originalBitmap.Height / 2f);
        
        // 旋转画布
        canvas.RotateDegrees(angle);
        
        // 绘制原始图像，使其居中
        canvas.DrawBitmap(originalBitmap, 
            new SKPoint(-originalBitmap.Width / 2f, -originalBitmap.Height / 2f));
    }

    return rotatedBitmap;
}

高级旋转技巧

带插值的平滑旋转

C#
public SKBitmap SmoothRotateImage(SKBitmap originalBitmap, float angle)
{
    // 创建一个新的位图，考虑旋转后的最大尺寸
    SKBitmap rotatedBitmap = new SKBitmap(
        (int)(Math.Abs(originalBitmap.Width * Math.Cos(angle * Math.PI / 180)) + 
              Math.Abs(originalBitmap.Height * Math.Sin(angle * Math.PI / 180))),
        (int)(Math.Abs(originalBitmap.Width * Math.Sin(angle * Math.PI / 180)) + 
              Math.Abs(originalBitmap.Height * Math.Cos(angle * Math.PI / 180)))
    );

    using (SKCanvas canvas = new SKCanvas(rotatedBitmap))
    {
        // 使用高质量的插值模式
        canvas.SetMatrix(SKMatrix.CreateRotationDegrees(angle, 
            rotatedBitmap.Width / 2f, 
            rotatedBitmap.Height / 2f));

        // 使用双线性插值绘制图像
        canvas.DrawBitmap(originalBitmap, 
            new SKRect(0, 0, originalBitmap.Width, originalBitmap.Height),
            new SKRect(0, 0, rotatedBitmap.Width, rotatedBitmap.Height),
            new SKPaint 
            { 
                FilterQuality = SKFilterQuality.High 
            });
    }

    return rotatedBitmap;
}

![image.png](https://www.otteach.cn/static/img/b93795dc6e5411af0bd1d7edc011c233.image.webp)

## 注意事项

- 旋转会改变图像的尺寸和质量
- 大角度旋转可能导致图像边缘出现锯齿
- 选择合适的插值模式可以提高旋转质量

## 性能建议

- 对于频繁旋转，考虑重用 `SKCanvas` 和 `SKBitmap`
- 使用 `SKFilterQuality` 平衡图像质量和性能
- 对于大图像，考虑异步处理

## 结语

SkiaSharp 提供了灵活且强大的图像旋转功能。通过合理使用旋转方法，可以轻松实现各种图像处理需求。