33 Virtualized Overscan. 33 of 95.
33/SCROLL BEHAVIOR/33 of 95
Virtualized Overscan
Render a little beyond the edge so scrolling never blanks.
The problem
Rendering only exactly-visible rows means fast scrolls outrun rendering and flash blank gaps.
The solution
An overscan buffer renders rows just outside view; adaptive overscan grows the buffer during fast scroll.
Experiment
Play with the values
4
1.5
How it works
- The viewport and row height define how many rows can be seen at once.
- The visible index range is computed from the scroll offset.
- An overscan buffer adds rows just outside that range.
- The buffer grows with scroll velocity so a fast flick does not run into blank space.
- Only that window is rendered.
- Rows are recycled as the window moves, instead of mounting the whole list.
Seen in
Data grids
Thousands of rows scroll smoothly by rendering only a window plus buffer.
Chat history
Long message lists stay performant without blank gaps.
File explorers
Huge directories render just what's near the viewport.
Feeds
Infinite content lists keep memory low while scrolling fast.