Serve Android's scrolling screenshot from the chat timeline - #492
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Android 12's screenshot tool extends a capture by asking the app which view scrolls and then for the pixels above and below the viewport, one tile at a time. GPUI paints the whole window into one surface, so the framework finds no scrolling view, and its wgpu surface cannot be read back. A transparent view covering the window answers for the timeline: Rust reports the list's rectangle, scrolls it to each tile relative to a row anchored at the start (rows measured for the first time move every pixel count above them), and replies once a presented frame is settled; the activity copies that frame out of the window with PixelCopy. Tail following, history paging and the reservation scroll-back are paused for the capture and the anchor is restored afterwards.
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Summary
ScrollCaptureBridgeview answers the system'sScrollCaptureCallbackfor the GPUI window: Rust reports the timeline's rectangle, scrolls it to each requested tile, and replies once a presented frame is settled; the activity copies that frame withPixelCopyinto the capture session's surface.ChatViewgains a capture session: tail following, history paging and the reservation scroll-back are paused, the origin is a row anchor (rows measured for the first time move every pixel count above them), tiles are clamped to measured content and never enter the history reservation, and the anchor is restored at the end.gpui-androidgains aScrollCaptureRequesthost event, a process-level callback andafter_next_frame; the host crate drives the settle loop (re-scroll after each frame until nothing moves and no Markdown build is pending, bounded to 12 frames).Test plan
cargo test -p tcode-ui(300 passed, incl. newscrolling_capture_moves_the_timeline_within_its_content_and_restores_it)cargo clippy -p tcode-ui --all-targets -- -D warningscargo ndk -t arm64-v8a clippy -p tcode-android(only the pre-existingi18n.rsthread_local warning on this target)androidTestcompile; newScrollCaptureBridgeTestcovers tile geometryiOS has no public API for this and is unchanged.