Summary

This PR implements the SMIL Snapshot Rendering lane for static SVG animation snapshots. It moves the animation runtime beyond time-zero rendering by evaluating configured snapshot times, composing active animation intervals, routing animated values through the same style/resource paths used by static rendering, and refreshing W3C Chrome-backed baselines for the enabled animation rows.

The work is split into three commits:

• bcc4ede3e implements the SMIL animation runtime behavior.
• bcd3aad78 hardens renderer/resource parity needed by animated snapshots.
• ab2531774 refreshes the W3C SMIL snapshot harness, baselines, and roadmap.

What Changed

SMIL animation runtime

• Added broader SMIL timing support for repeat events, repeat(n) eventbase timing, self-sync recurrence, future syncbase start-time queries, restart truncation, finite max handling for indefinite intervals, and half-open active interval boundaries.
• Expanded interpolation coverage for scalar values, number lists, path data, transform values, motion paths, colors, currentColor, and inherit.
• Added fallback behavior for unsupported or non-interpolable values, including midpoint discreteness and to-only non-interpolable routing for class, display, href/resource, filter, unit, and enum attributes.
• Preserved browser-like composition order for animateMotion plus animateTransform, including additive and non-additive combinations.
• Preserved raw animation attribute strings so values such as currentColor, inherit, and resource references survive until runtime resolution.
• Added namespace-aware animation attribute routing for href, xlink:href, xml:*, style, class, presentation attributes, and custom attributes.
• Re-applies compatibility styles and invalidates style caches when animated class/style mutations affect selector resolution.

Rendering and resource parity

• Rebinds same-document deferred paint servers after animated document cloning so animated gradients, currentColor, and local paint references resolve against the animated clone instead of the source document.
• Improves gradient and pattern inheritance by checking whether attributes are explicitly declared rather than assuming default values were intentionally set.
• Guards recursive patterns and non-invertible pattern transforms.
• Hardens filter behavior for invalid color matrix values, negative blur/morphology inputs, and morphology kernel rounding.
• Adds support for transformed use clip paths and marker suppression in temporary marker compilation.
• Improves CSS clip: rect(...) parsing, including whitespace syntax, auto, px, and legacy comma-offset behavior.
• Handles empty image data in the Skia asset loader without throwing.
• Fixes spot-lit specular code generation/runtime parameter parity.

W3C harness and baselines

• Adds explicit W3C animation seek times so enabled snapshot rows compare the same animation frame used by their Chrome references.
• Updates the Chrome override capture script to read seek times from W3CTestSuiteTests, wait for a real iframe document, use an explicit capture-ready marker, avoid duplicate readiness callbacks, and simulate the pre-seek interaction needed by animate-elem-52-t.
• Adds Chrome overrides for 58 enabled SMIL rows plus animate-pservers-grad-01-b, and refreshes filters-composite-05-f.
• Enables the implemented W3C animation rows and keeps browser-runtime-only rows skipped with explicit reasons.
• Updates the skipped-tests roadmap with the completed SMIL snapshot implementation status and remaining policy/runtime gaps.

Remaining Explicit Policy Skips

The remaining skipped SMIL rows are not hidden failures in enabled coverage:

• Deprecated animateColor rows where modern Chrome captures the fixture as a no-op and the suite needs a non-Chrome static reference policy before enabling.
• Browser runtime rows requiring hyperlink activation, access keys, wallclock timing, pointer hit-testing, hover/mouse event sequencing, or embedded animated image script/runtime behavior.
• Deeper static parity rows such as animate-elem-90-b and animate-elem-91-t, where partial routing is covered but full selector guide-fill or display/use/resource parity remains broader than the static snapshot lane.

Validation

Ran the required local validation after implementation:

• dotnet format Svg.Skia.slnx --no-restore
• node --check scripts/capture_w3c_chrome_overrides.mjs
• git diff --check
• dotnet build Svg.Skia.slnx -c Release --no-restore
• dotnet test tests/Svg.Skia.UnitTests/Svg.Skia.UnitTests.csproj -f net10.0 -c Release --no-restore --filter "FullyQualifiedName~SvgAnimationControllerTests"
• dotnet test tests/Svg.Skia.UnitTests/Svg.Skia.UnitTests.csproj -f net10.0 -c Release --no-restore --filter "DisplayName~animate-"
• dotnet test Svg.Skia.slnx -c Release --no-restore

Results:

• Release build passed with existing warnings only.
• SvgAnimationControllerTests: 72 passed.
• W3C animation sweep: 63 passed, 17 explicit policy/runtime skips.
• Full solution tests: 2190 W3C/Svg.Skia rows reported from Svg.Skia.UnitTests with 2122 passed and 68 explicit skips; all other project test assemblies passed.

Notes

• externals/SVG was checked after formatting. Accidental submodule formatting churn was reverted, and the submodule is clean.
• The PR summary file itself is intentionally left uncommitted per request.