Retained Scene Graph Usage

SKSvg keeps a compiled retained scene graph in RetainedSceneGraph. That graph is represented by SvgSceneDocument and is the bridge between authored SVG DOM and the low-level ShimSkiaSharp.SKPicture command model.

What the retained scene graph contains

SvgSceneDocument stores:

the compiled root SvgSceneNode,
node lookups by element address and id,
resource lookups for clip paths, masks, filters, gradients, patterns, and markers,
compilation-root boundaries used for incremental refresh,
the document instance that backs the compiled scene.

That makes it the right surface for inspection, subtree rendering, incremental mutation, and hit testing.

Ensuring the scene graph exists

SKSvg builds and caches the scene graph during normal rendering, and TryEnsureRetainedSceneGraph(...) lets callers force that state explicitly:

using Svg.Skia;

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

if (svg.TryEnsureRetainedSceneGraph(out var scene) && scene is not null)
{
    var root = scene.Root;
    var revision = scene.Revision;
}

You can also check HasRetainedSceneGraph when a boolean is enough.

Looking up nodes and resources

The most common lookup helpers are:

TryGetRetainedSceneNode(SvgElement element, out SvgSceneNode? node)
TryGetRetainedSceneNode(string addressKey, out SvgSceneNode? node)
TryGetRetainedSceneNodeById(string id, out SvgSceneNode? node)
TryGetRetainedSceneNodes(...)
TryGetRetainedSceneResource(...)
TryGetRetainedSceneResourceById(...)

using Svg.Skia;

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

if (svg.TryGetRetainedSceneNodeById("layer-a", out var node) && node is not null)
{
    var elementId = node.ElementId;
    var hitTargetId = node.HitTestTargetElement?.ID;
    var bounds = node.TransformedBounds;
}

Rendering the whole scene or one subtree

The retained-scene helpers can render the full compiled scene or a single node without going back through the original source text:

using Svg.Skia;

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

using var scenePicture = svg.CreateRetainedSceneGraphPicture();

if (svg.TryGetRetainedSceneNodeById("layer-a", out var node) && node is not null)
{
    using var layerPicture = svg.CreateRetainedSceneNodePicture(node);
}

This is useful for previews, editor overlays, diagnostics, or selective export flows.

Mutating through the retained scene graph

For retained-scene refresh, resolve and mutate the element from the scene graph's own document instance:

using System.Drawing;
using Svg;
using Svg.Skia;

using var svg = new SKSvg();
svg.FromSvg(
    "<svg width=\"80\" height=\"40\">" +
    "  <rect id=\"rect-a\" x=\"10\" y=\"8\" width=\"24\" height=\"12\" fill=\"red\" />" +
    "</svg>");

var scene = svg.RetainedSceneGraph!;
var rect = (SvgRectangle)scene.SourceDocument!.GetElementById("rect-a")!;
rect.Fill = new SvgColourServer(Color.BlueViolet);

svg.TryApplyRetainedSceneMutationByIdAndRender("rect-a", new[] { "fill" }, out _);

That guarantees the mutation is applied against the same document instance the current retained scene was compiled from.

When the retained path is not enough

Not every mutation can stay incremental. If a call to ApplyRetainedSceneMutation(...) or TryApplyRetainedSceneMutation... returns an unsuccessful result, rebuild from the document instead:

if (!svg.TryApplyRetainedSceneMutationByIdAndRender("root", new[] { "viewBox" }, out _))
{
    svg.FromSvgDocument(scene.SourceDocument);
}

Structural edits and root-scene changes are the common cases that still require a full rebuild.