Never break up a cell inside a cell that stays in 2D - #2407
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A subscript (and a matrix, an at(), a diff() fraction) has no linear form, so it is always drawn in 2D. CollectWideCells() still descended into it and BreakUpCells() linearized the wide fractions and parentheses inside it. Only a cell that is itself broken into lines hands its contents to the draw list, so those cells were positioned and drawn by nobody (a wide subscript simply vanished), were only partly visible, and UnBreakUpCells(), walking the same draw list, never returned them to 2D. CollectWideCells() now only searches the contents of a cell it collected itself and records which wide cell each one was found in, and BreakUpCells() skips a cell whose containing wide cell did not actually break up. Debug builds assert the invariant in Cell::Draw(). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01V5Yz1a2PmuAUtJ7zYKsmuX
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Requested by Gunter · project thread
Before: a wide fraction or parenthesis inside a subscript (e.g.
a[(x_1+...)/(y_2+...)]in a narrow window) was partly broken into lines or vanished entirely, and stayed that way after the window was widened again.After: everything inside a subscript stays in 2D, like the subscript itself.
A subscript,
SubSupCell,at(), matrix anddiff()fraction have no linear form and always draw their contents in 2D.CollectWideCells()still descended into them, andBreakUpCells()linearized the wide cells it found there. Only a cell that is itself broken into lines hands its contents to the draw list, so those cells were positioned and drawn by nobody, andUnBreakUpCells()(which walks that same draw list) never returned them to 2D.How:
CollectWideCells()now records, for each wide cell, the wide cell it was found in, and only searches the contents of cells it collected itself;BreakUpCells()skips a cell whose containing wide cell didn't actually break up. No extra tree walks, so no layout slowdown. Debug builds additionally assert inCell::Draw()that a cell drawn in 2D has no broken contents.Tests: new
test_LayoutInvariantsscenario "Nothing inside a subscript is broken into lines" (12 failures onmain, passes now); all 48 unit tests and the Maxima-backed*Cellsbatch tests pass. Checked in the real app: onmainthe subscript's fraction is not drawn at all; with this change it is drawn in 2D. Also updated NEWS.md, AGENTS.md and the layout skill (new invariant 5).🤖 Generated with Claude Code
https://claude.ai/code/session_01V5Yz1a2PmuAUtJ7zYKsmuX
Generated by Claude Code