SkiaSharp转换SVG为PNG时图像未填满画布问题求助

我尝试使用SkiaSharp将SVG图像转换为PNG，再转为PdfSharp的XImage对象以添加至PDF页面（因PdfSharp不直接支持SVG格式）。已编写对应代码：

private XImage LoadSvgIcon(string iconUrl)
{
    XElement root = XElement.Load(iconUrl);

    using (Stream xmlStream = new MemoryStream())
    {
        root.Save(xmlStream);
        xmlStream.Flush();
        xmlStream.Position = 0;
                
        var svg = new SkiaSharp.Extended.Svg.SKSvg();
        svg.Load(xmlStream);
                
        var bitmap = new SKBitmap((int)svg.CanvasSize.Width, (int)svg.CanvasSize.Height);
        var canvas = new SKCanvas(bitmap);
                
        var p = new SKPaint();
        p.Color = SKColor.Parse("#219de1");
        canvas.DrawPaint(p);

        canvas.DrawPicture(svg.Picture);

        using (var skData = SKImage.FromBitmap(bitmap).Encode(SKEncodedImageFormat.Png, 100))
        {
            Stream stream = new MemoryStream();
            skData.SaveTo(stream);
            return XImage.FromStream(stream);
        }
    }
}

虽将画布大小设置为SVG的CanvasSize，但SVG图像仍未填满整个画布（画布为淡蓝色背景，SVG自身带红色背景及内部图标，未占满画布空间），请问遗漏了什么？

问题核心是SVG的实际内容尺寸（由Picture.CullRect定义）和画布尺寸不匹配，直接绘制svg.Picture只会按它自身的原始尺寸渲染，不会自动拉伸填满画布。需要添加缩放适配逻辑，修改后的代码如下：

private XImage LoadSvgIcon(string iconUrl)
{
    XElement root = XElement.Load(iconUrl);

    using (Stream xmlStream = new MemoryStream())
    {
        root.Save(xmlStream);
        xmlStream.Flush();
        xmlStream.Position = 0;
                
        var svg = new SkiaSharp.Extended.Svg.SKSvg();
        svg.Load(xmlStream);
                
        var bitmap = new SKBitmap((int)svg.CanvasSize.Width, (int)svg.CanvasSize.Height);
        var canvas = new SKCanvas(bitmap);
                
        var p = new SKPaint();
        p.Color = SKColor.Parse("#219de1");
        canvas.DrawPaint(p);

        // 获取SVG内容的实际边界范围
        var pictureBounds = svg.Picture.CullRect;
        if (!pictureBounds.IsEmpty)
        {
            // 计算缩放比例：让SVG内容填满画布，同时保持宽高比例
            float scaleX = svg.CanvasSize.Width / pictureBounds.Width;
            float scaleY = svg.CanvasSize.Height / pictureBounds.Height;
            float scale = Math.Max(scaleX, scaleY);

            // 计算偏移量，让SVG在画布中居中显示
            float offsetX = (svg.CanvasSize.Width - pictureBounds.Width * scale) / 2;
            float offsetY = (svg.CanvasSize.Height - pictureBounds.Height * scale) / 2;

            // 创建变换矩阵：先平移到居中位置，再执行缩放
            var matrix = SKMatrix.CreateTranslation(offsetX, offsetY);
            matrix = SKMatrix.Concat(matrix, SKMatrix.CreateScale(scale, scale));
            
            canvas.SetMatrix(matrix);
        }

        canvas.DrawPicture(svg.Picture);

        using (var skData = SKImage.FromBitmap(bitmap).Encode(SKEncodedImageFormat.Png, 100))
        {
            Stream stream = new MemoryStream();
            skData.SaveTo(stream);
            // 重置流指针到起始位置，否则XImage无法读取内容
            stream.Position = 0;
            return XImage.FromStream(stream);
        }
    }
}

额外补充两个关键细节：

• 新增stream.Position = 0：SaveTo操作后流的指针会停在末尾，必须重置才能让XImage读取到完整内容
• 若不需要保持宽高比例，可直接用scaleX和scaleY分别缩放，去掉scale = Math.Max(...)的逻辑，直接创建SKMatrix.CreateScale(scaleX, scaleY)即可

内容的提问来源于stack exchange，提问作者developer82