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Hit Testing and Model Editing

Hit testing in picture coordinates

SKSvg exposes hit testing for both drawables and SVG elements:

using System.Linq;
using ShimSkiaSharp;
using Svg.Skia;

using var svg = new SKSvg();
svg.Load("image.svg");

var element = svg.HitTestElements(new SKPoint(10, 10)).FirstOrDefault();
var drawable = svg.HitTestDrawables(new SKRect(0, 0, 40, 40)).FirstOrDefault();

Hit testing on transformed canvases

When the picture is drawn through a transformed canvas, convert the input point or rectangle back into picture space first:

using ShimSkiaSharp;
using Svg.Skia;

using var svg = new SKSvg();
svg.Load("image.svg");

var canvasMatrix = SKMatrix.CreateScale(2f, 2f);
if (svg.TryGetPicturePoint(new SKPoint(50, 50), canvasMatrix, out var picturePoint))
{
    var hits = svg.HitTestElements(picturePoint);
}

There are overloads that take the canvas matrix directly:

• HitTestElements(SKPoint point, SKMatrix canvasMatrix)
• HitTestElements(SKRect rect, SKMatrix canvasMatrix)
• HitTestDrawables(SKPoint point, SKMatrix canvasMatrix)
• HitTestDrawables(SKRect rect, SKMatrix canvasMatrix)

Avalonia control hit testing

The Skia-backed Avalonia.Svg.Skia.Svg control exposes HitTestElements(Point point) in control coordinates, so the control handles the coordinate transform for you.

Model editing

Once you identify the commands you care about, update the model and rebuild:

using System.Linq;
using ShimSkiaSharp;
using Svg.Skia;

using var svg = new SKSvg();
svg.Load("image.svg");

foreach (var cmd in svg.Model?.Commands?.OfType<DrawPathCanvasCommand>() ?? Enumerable.Empty<DrawPathCanvasCommand>())
{
    if (cmd.Paint?.Color is { } color)
    {
        cmd.Paint.Color = new SKColor(color.Red, 0, 0, color.Alpha);
    }
}

svg.RebuildFromModel();

In Avalonia, the same pattern applies through SvgSource.RebuildFromModel().