Scroll captures

Long-form scrolling captures (one tall PNG that stitches the whole scrollable region) and animated GIFs of the scroll itself, driven through the renderer extension pipeline.

At a glance

Kinds	render/scroll/long, render/scroll/gif
Schema version	n/a (image-only)
Modules	:data-scroll-core (pure JVM — planners, stitcher, GIF encoder, axis), :data-scroll-android (the Android AndroidComposeTestRule-bound scroll drivers used by :renderer-android)
Render mode	default
Cost	medium (extra renders per scroll step)
Token usage	Image-only — ~1.5 k tok per render/scroll/* PNG read; payload itself is a path. See token usage.
Transport	path (PNG / GIF)
Platforms	Android · Desktop · shared

What it answers

• What does the entire scrollable region look like, end to end, not just the viewport at rest?
• What does the scroll motion look like over time (entry animations, sticky headers settling, LazyColumn item placement)?
• Does a nestedScroll collapse / expand land in the right state at the end of a fling?

data/scroll/core ships the pure-JVM scroll primitives (ScrollAxis, ScrollLongFramePlan / ScrollGifFramePlan planners, ScrollSliceStitcher, ScrollGifEncoder, ScrollPreviewExtension). data/scroll/android ships the AndroidComposeTestRule-bound ScrollDriver (driveScrollByViewport, driveScrollBy, driveScrollToStart, driveScrollToEnd, remainingScrollPx) — the Android renderer composes both. The Compose Desktop renderer pulls just data-scroll-core and drives the scrollable through runComposeUiTest directly, sharing the pure-JVM planners and stitcher with the Android path.

What it does NOT answer

• Scroll is renderer-side only — it produces image artifacts, not a JSON payload, so it has no kind on the daemon’s initialize.capabilities.dataProducts list. There is no data-scroll-connector. It never round-trips through data/fetch or data/subscribe; instead the renderer drives it directly via PreviewPipelineStep / scenario-driver hooks.
• It does not measure scroll performance — for that, instrument compose/recomposition over the same scrolled frames.

Use cases

• Render a tall settings screen as one PNG for design review.
• GIF a LazyColumn to verify item-key stability across data changes.
• Capture the full scroll of a Wear ScalingLazyColumn to confirm the curvature target.

Payload shape

Image-only artifacts. Produced via :data-scroll-core extensions. Output paths under build/compose-previews/renders/<id>-long.png and build/compose-previews/renders/<id>.gif.

Enabling

Annotate the preview with the matching multi-preview annotation (e.g. @ScrollingPreview) — see skills/compose-preview/references/capture-modes.md for the multi-preview / scenario annotations the scroll extension recognises.

Companion products

• Recomposition — compose/recomposition to attribute scroll cost to specific composables.
• History diff — history/diff/regions against a long-PNG baseline to catch list-item layout regressions.