Add data cursors and pinned datatips #2

Activity

1. thclark

   changed the title [-]Add a GPU picking pass[/-] [+]Add data cursors and pinned datatips[/+] on Sep 17, 2026
2. thclark

   added

   kind: featureA new capabilityA new capability

   area: codeLibrary, viewer or tooling source codeLibrary, viewer or tooling source code

   crate: irMostly related to the ironlab-ir figure model crateMostly related to the ironlab-ir figure model crate

   crate: sceneMostly related to the ironlab-scene layout and scene compilation crateMostly related to the ironlab-scene layout and scene compilation crate

   crate: viewerMostly related to the ironlab-viewer native egui viewer crateMostly related to the ironlab-viewer native egui viewer crate

   priority: mediumDo in the normal course of workDo in the normal course of work

   flow: plan-requiredA plan is required before this can progress to ai-readyA plan is required before this can progress to ai-ready

   on Oct 22, 2026
3. thclark commented on Oct 26, 2026

   

   thclark

   on Oct 26, 2026

   OwnerAuthor

   More actions

   A rudimentary form of datatips for bars, stairs and cells now exists, delivered in the bars and histograms epic (#173). It should be taken into account here, and probably replaced or reworked, so that every artist ends up with consistent datatips.

   What exists

   • Hits. The scene compiler records a rectangle hit for each drawn bar and cell, and a step hit for each bin of a stairs artist (BarHit, CellHit and StepHit in crates/ironlab-scene/src/hit.rs). These sit alongside the existing point samples of series and the inverse transforms of images.
   • Tip variants. The canvas resolves them into three new variants of Tip in crates/ironlab-canvas/src/interaction.rs: Tip::Bar, Tip::Step and Tip::Cell. Each has its own callout text in figure_canvas.rs, mirrored in the web outcome.
     • A bar tip reports the value, the base and the segment from base to end.
     • A step tip reports the bin's edges and value.
     • A cell tip reports its row, column and value, the latter in the same kinds as a pixel (category, index or value).
   • Category names. All three name the category under the pointer when the category axis has text tick labels and the bar's position, or the cell's centre, equals a tick value.
   • Histogram bins. When an artist carries a binning record (ADR 0029), its tip also reports the count and density of the whole bin, recovered from the record.
   • Precedence. Colourbar, then point, then step, then bar, then cell, then pixel.

   Why it should be revisited

   Each artist kind gained its own hit type, its own Tip variant and its own callout format, because no common model of what a datatip reports exists yet. The result works, but it repeats the pattern of the pixel and colourbar tips rather than converging on one design. The precedence order between kinds is a fixed list rather than a rule.

   This issue, together with GPU picking (#1), should define:

   • one model of a picked element: artist, element index and the data it reports;
   • one callout format;
   • one rule for what wins when several elements lie under the pointer.

   Pinned datatips would then be built on that model, and bars, stairs, cells, series and images would move onto it. The category-name lookup and the bin readings from binning records are worth keeping as parts of that model.

   This is recorded for planning only; nothing about it is to be changed in #173.