Performance and Retained-Scene Refresh

The load and refresh cost of an SVG is not one number. In Svg.Skia the work is split across document parsing, retained-scene compilation, shim-model creation, native SKPicture materialization, and any later raster export.

This matters when a device looks "slow to load" because the bottleneck may be DOM parsing, scene compilation, PNG encoding, or a full rebuild after a small mutation.

Measure the staged pipeline

The benchmark project includes a dedicated profiler for one SVG file:

dotnet run --project tests/Svg.Skia.Benchmarks/Svg.Skia.Benchmarks.csproj -c Release -- --profile-svg '/Users/wieslawsoltes/Downloads/solar battery.svg' 20

That command reports separate timings for:

parsing text into SvgDocument,
compiling the retained SvgSceneDocument,
creating the shim SKPicture model,
creating the native SkiaSharp.SKPicture,
rendering to a bitmap,
encoding to PNG,
full SKSvg.FromSvg(...),
control-like source loading,
full FromSvgDocument(...) rebuild after a mutation,
retained-scene mutation refresh.

Example profile

Example output from osx-arm64, Release, 20 iterations, for /Users/wieslawsoltes/Downloads/solar battery.svg (29,974 bytes):

Stage	Mean
Parse `SvgDocument` from string	`2.46 ms`
Compile retained scene	`5.08 ms`
Create shim picture model	`0.04 ms`
Create native `SKPicture`	`0.53 ms`
Render native picture to bitmap	`3.77 ms`
Encode native picture to PNG	`13.85 ms`
Load via `SKSvg.FromSvg(...)`	`12.39 ms`
Control-like source load	`11.14 ms`
Mutate + full `FromSvgDocument(...)` rebuild	`16.11 ms`
Mutate + retained-scene refresh	`12.73 ms`

Treat those numbers as a shape, not a promise. CM4, CM5, desktop ARM, and different output resolutions will change the absolute timings.

Hot paths to watch

The staged profile above points at the current hot paths:

retained-scene compilation is the main load-time cost inside SKSvg,
native picture creation is comparatively small,
PNG encoding can dominate end-to-end export time even when rendering itself is fast,
retained-scene mutation refresh is cheaper than a full FromSvgDocument(...) rebuild for small localized edits.

Text-heavy documents can push more cost into text compilation and measurement than purely geometric assets, so profile representative files instead of relying on one benchmark.

Retained-scene refresh APIs

SKSvg exposes three refresh helpers for localized DOM edits:

TryApplyRetainedSceneMutationAndRender(SvgElement element, IReadOnlyCollection<string>? changedAttributes, out SvgSceneMutationResult? result)
TryApplyRetainedSceneMutationAndRender(string addressKey, IReadOnlyCollection<string>? changedAttributes, out SvgSceneMutationResult? result)
TryApplyRetainedSceneMutationByIdAndRender(string id, IReadOnlyCollection<string>? changedAttributes, out SvgSceneMutationResult? result)

Example:

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);

if (!svg.TryApplyRetainedSceneMutationByIdAndRender("rect-a", new[] { "fill" }, out var result))
{
    svg.FromSvgDocument(scene.SourceDocument);
}

The returned SvgSceneMutationResult reports whether the refresh succeeded and how many compilation roots had to be recompiled.

Picking the right refresh path

Use retained-scene refresh when:

the change is localized to one element or a small subtree,
you know which attributes changed,
the renderer is already holding a retained scene graph,
you want the current Picture refreshed without a full DOM-to-scene recompilation.

Use FromSvgDocument(...) when:

the root element changed,
structure was added or removed,
the mutation touches a case that cannot be refreshed incrementally,
you want the simplest and most predictable rebuild path.

Use ReLoad(...) when:

the underlying source is unchanged,
only SvgParameters changed,
the original source path or stream should be reparsed with different CSS or entities.