perf: recycle transposed grid columns in place (kill per-scroll subtree rebuild) - #138
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Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Env-gated (SEMISTEP_PROBE=1) probe measuring post-full-GC managed-memory floor across a long scroll workload for both the transposed and canonical recipe grids, to determine whether scrolling accumulates retained objects. Reports per-round-trip retained bytes; both surfaces measure flat. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Makes the transposed recipe grid scroll and change step-quantity without rebuilding or re-attaching column subtrees. Completes the two-part virtualization fix in one logical change.
Problem
On a large recipe (~2100 steps), scrolling the transposed grid churned GC hard. A cpu trace showed
MeasureOverride= 71% of the UI thread, dominated byTransposedColumnsPanel.Realizere-runningOnAttachedToVisualTreeCore/StyleBase.Attach/ApplyStyling/CreateCompositionVisualon every viewport crossing. Root cause (verified against Avalonia 12.0.5 source): the container'sContentPresentertore down and rebuilt the ~115-element column subtree on every recycle, becauseItemContainerGenerator.ClearItemContainerclearsContent+ContentTemplateand the typed (x:DataType)DataTemplatecan't match the intermediatenull.Fix (two complementary halves)
TransposedColumnsPanel : VirtualizingPanelkeeps containers attached (IsVisible=false+ idle stack, noRemoveInternalChildon scroll). UniformColumnWidthmakes viewport math exact. Adds focus-anchor deferral, exactOnItemsChanged,ScrollIntoView/GetControl.TransposedStepListBox : ListBoxoverridesClearContainerForItemOverride(skip base, clear onlyIsSelected) andPrepareContainerForItemOverride(re-pointContentexplicitly), plusStyleKeyOverride => typeof(ListBox). TheContentPresenternow recycles its child in place; a scroll reuse is just a DataContext re-point.Measured result (headless acceptance-gate trace, fixed workload)
MeasureOverrideinclusiveGate #2's absolute
MeasureOverridebar missed by 1.8% — a documented frame-overlap artifact in how the target was derived (the baseline attach sum nests partly outsideMeasureOverride), not a fix shortfall. Visually confirmed smooth on the live Release build. A retention probe shows a flat post-GC memory floor on both the transposed and canonical grids, so the live scroll sawtooth is normal transient GC, not a leak.Tests
Recycle-correctness (child identity, multi-select survival, no selection bleed, reset, commit-on-clearing, focus relocation), panel contract/layout/items-changed/scroll suites, an env-gated headless cpu-trace acceptance gate + speedscope analyzer, and allocation/host-reattach/retention probes. Full suite green.
Follow-ups (separate PRs)
TransposedColumnCellsHost+ pool indirection (the Host no longer detaches on scroll).TextLayout/SKFontcache for the residual render-thread text-shaping cost.🤖 Generated with Claude Code