apple-text-viewport-rendering

TextKit 2 viewport rendering dictates scrolling by mapping line fragment geometry to document coordinates. It evaluates layoutFragmentFrame, typographicBounds, and glyphOrigin to determine which fragments render on-screen versus off-screen during scroll transitions.

Debug TextKit 2 viewport decisions by comparing layoutFragmentFrame values against document coordinates. Inspect fragment geometry and usage bounds to identify mismatches between expected and actual rendering surfaces within custom text views.

The relationship between layoutFragmentFrame and document coordinates in TextKit 2 defines the text view's spatial mapping. Converting fragment coordinates to document coordinates ensures accurate visual rendering and correct scrolling edge case handling.

Font substitution timing affects visual rendering in TextKit 2 by altering line fragment geometry before the viewport layout finalizes. Late substitutions shift typographicBounds and glyphOrigin, causing unexpected on-screen layout estimates and rendering surface placements.

Incorrect off-screen layout estimates in TextKit 2 usually stem from misinterpreting usage bounds and fragment frames. Failing to properly convert between fragment coordinates and document coordinates leads to inaccurate viewport behavior predictions.

Yes, you can diagnose scrolling edge cases in custom text views by analyzing TextKit 2 viewport layout mechanisms. Interpreting fragment geometry and coordinate conversion reveals the root causes of rendering surface anomalies and scroll jumps.