perf(chat): use content-visibility for off-screen messages#599
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HUQIANTAO wants to merge 1 commit into
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perf(chat): use content-visibility for off-screen messages#599HUQIANTAO wants to merge 1 commit into
HUQIANTAO wants to merge 1 commit into
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The message list renders up to 300 messages (MAX_MESSAGES_IN_MEMORY) simultaneously. Each MessageItem includes markdown parsing, code highlighting (Shiki), tool call groups, and widget iframes — creating significant DOM node count and paint cost even for off-screen messages. Add CSS content-visibility:auto to messages older than the last 50. This tells the browser to skip layout and paint for off-screen content while preserving scroll height via contain-intrinsic-block-size. The browser natively manages which messages to render based on viewport visibility, with zero JavaScript overhead. This is a pure CSS optimization — no changes to scroll behavior, message ordering, or the existing use-stick-to-bottom anchor system.
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HUQIANTAO
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Problem
The message list renders up to 300 messages (
MAX_MESSAGES_IN_MEMORY) simultaneously via a plain.map()call. EachMessageItemincludes markdown parsing, Shiki code highlighting, tool call groups, and widget iframes — creating significant DOM node count and paint cost even for messages far off-screen.Fix
Apply CSS
content-visibility: autoto message wrappers older than the last 50 messages. This is a browser-native rendering optimization:content-visibility: auto— tells the browser to skip layout and paint for off-screen elementscontain-intrinsic-block-size: 80px— provides a height estimate so scroll height is preserved without renderingThe browser natively manages which messages to render based on viewport visibility, with zero JavaScript overhead. This is a pure CSS optimization — no changes to scroll behavior, message ordering, or the existing
use-stick-to-bottomanchor system.Messages within the last 50 (the typical viewport + buffer) are always rendered eagerly, ensuring no visual regression for the active conversation area.