feat (display/rtplot): extract RTScaledWidgetRepresentation + add show_scale_labels to Tank

[emilioheredia-source]

Summary

Refactors the Tank widget's JavaFX wiring to eliminate the duplication that
existed between TankRepresentation and (the future) RTProgressBarRepresentation,
and adds a new show_scale_labels property to TankWidget and the underlying
YAxisImpl canvas axis.

This PR depends on: tank_scale_refactor (already merged as #3760).
It is recommended to merge this after #3766
(parallel_rendering preference for RTTank), but the two PRs are independent —
each applies cleanly on top of master without the other.
Merging this PR, also sets up the base class and show_scale_labels infrastructure
needed by the RTTank-based Progress Bar refactor, which will be submitted as the next PR.

---

What Changed

New: RTScaledWidgetRepresentation<W> abstract base class

A generic base for all widget representations whose JFX node is an RTTank.
Handles everything that depends only on the ScaledPVWidget contract:

• Creating and throttle-configuring the RTTank
• Forwarding PV value and display-range changes to the tank
• Evaluating alarm limit lines from PV metadata or widget properties
• 90° orientation transform for horizontal layout
• Scheduling representation updates on property changes

Subclasses provide four template methods:

Method	Purpose
isHorizontal()	Read the widget's own horizontal property
registerLookListeners()	Add listeners on widget-specific appearance properties
unregisterLookListeners()	Remove those listeners
applyLookToTank(w, h)	Push current appearance to the tank

configureTank() is an optional no-op hook called once after tank creation.

Result: TankRepresentation collapses from ~270 lines to ~90 lines of
widget-specific code. RTProgressBarRepresentation (PR3) is ~110 lines.

ScaledPVWidget — new propShowScaleLabels descriptor

show_scale_labels (boolean, default true) is added to ScaledPVWidget
so both Tank and ProgressBar inherit it without duplication.

TankWidget — new show_scale_labels property

Exposes show_scale_labels in the property editor. Default true preserves
existing behaviour.

RTTank — setScaleLabelsVisible(boolean)

Delegates to both YAxisImpl instances (left and right scale). Each axis
fires requestLayout()/requestRefresh() internally via plot_part_listener
when its state changes, so no extra need_layout or requestUpdate() calls
are needed in RTTank.

YAxisImpl — ticks-only rendering mode (show_labels)

Method	Behaviour when show_labels = false
getDesiredPixelSize	Returns TICK_LENGTH (10 px) immediately — no label metrics computed
getPixelGaps	Returns {0, 0} — rotated labels no longer overhang endpoints
paint	Skips drawTickLabel and paintLabels; tick marks and axis line draw normally

show_labels is volatile because it is read on the Java2D render thread
and written on the JFX application thread.

setScaleLabelsVisible has an early-return guard to suppress spurious
relayout when the value has not actually changed.

Use case: stacked widgets sharing a single labelled scale

---

Backward Compatibility

• Default show_scale_labels=true — existing .bob files load and display
  identically.
• New XML element <show_scale_labels> is silently ignored by older Phoebus.
• RTScaledWidgetRepresentation is package-private. No public API change.

---

Files Changed

RTScaledWidgetRepresentation.java | 343 +++ (new)
TankRepresentation.java | 241 +/--
RTTank.java | 102 ++-
YAxisImpl.java | 38 ++-
ScaledPVWidget.java | 36 ++-
TankWidget.java | 39 +/-
Messages.java | 2 +
messages.properties | 2 +
8 files changed, ~548 insertions, ~255 deletions

---

Design Decisions

Decision	Rationale
show_labels as volatile	The field is written on the JFX thread (setScaleLabelsVisible) and read on the Java2D render thread (paint, getDesiredPixelSize). Without volatile the write may not be visible to the render thread.
No extra requestUpdate in setScaleLabelsVisible	The YAxisImpl axes call requestLayout()/requestRefresh() themselves when the value changes; these propagate to RTTank.need_layout and requestUpdate() via plot_part_listener. A second explicit call would cause a redundant double-render.
show_scale_labels in ScaledPVWidget	Both Tank and ProgressBar benefit from the feature. Placing the descriptor in the base class avoids declaring it twice.
Descriptor only, not a defineProperties entry in ScaledPVWidget	Each concrete widget decides whether to expose the property, allowing Tank to default true and a future Meter or Thermometer to choose differently.

[sonarqubecloud]

Quality Gate passed

Issues
27 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[shroffk]

This PR depends on: tank_scale_refactor (already merged as #3760).
It is recommended to merge this after #3766

both are merged

this PR is ready to test and merge now

[georgweiss]

@shroffk , will test next week

[shroffk]

We could also do this at the codeathon

[emilioheredia-source]

Rebased onto current master (the branch was ~265 commits behind) and squashed into one commit; the diff is what it was, minus the items below.

The rebase turned up one real problem, now fixed: the branch had moved the Tank's border descriptor into ScaledPVWidget under the name border_width, which would have renamed the tank_border_width property that shipped with 5.0.x (that is what TankWidgetUnitTest caught). TankWidget keeps tank_border_width; the shared descriptor moves to #3768 where the new widgets need it.

Other changes since the April version, from a review pass before re-submitting:

• YAxisImpl.getDesiredPixelSize() did not store the region in ticks-only mode, which could NPE in paint() if the labels were switched on between layout and paint; fixed. Ticks-only width is TICK_LENGTH + 1 so the tick is not clipped by one pixel, and the label layout is skipped in that mode.
• RTScaledWidgetRepresentation no longer skips the range update on pure value updates (the April version did, with a justification that AxisPart.setValueRange() makes moot); behaviour is now exactly the old TankRepresentation.
• setInnerPadding()/setFlatTrack() and the configureTank() hook are gone from this PR; nothing here used them, they come with feat (display): RTTank-based Progress Bar backend — scale, alarm limits, and stacking support (opt-in via preference) #3768.
• The old last commit "remove Activator.parallel_rendering dependency" was dropped: master has that hook through perf(rtplot): add parallel_rendering preference for RTTank UpdateThrottle #3766, so after the rebase it had turned into a revert.
• TankWidgetUnitTest covers show_scale_labels; French translation added.

Two related PRs, in case it helps to plan the codeathon:

• a small independent fix for two Tank regressions from TankWidget: dual scales, alarm limit lines, ScaleFormat enum, and ScaledPVWidget base class #3760 (inverted range, label format on linear scales): fix (rtplot): RTTank ignores inverted ranges and the label format on linear scales #3929
• feat (display): RTTank-based Progress Bar backend — scale, alarm limits, and stacking support (opt-in via preference) #3768 (Progress Bar) is rebased on top of this one, and the Thermometer PR feat (display): RTTank-based Thermometer backend — numeric scale, alarm limits, and glass bulb (opt-in via preference) #3930 on top of feat (display): RTTank-based Progress Bar backend — scale, alarm limits, and stacking support (opt-in via preference) #3768.

[sonarqubecloud]

Quality Gate passed

Issues
18 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud