Matt Gilman created NIFI-16447:
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Summary: Give the reusable canvas one visibility pass, one
selection gate, and one preview flag
Key: NIFI-16447
URL: https://issues.apache.org/jira/browse/NIFI-16447
Project: Apache NiFi
Issue Type: Improvement
Components: Core UI
Reporter: Matt Gilman
Assignee: Matt Gilman
h2. Background
The reusable canvas renderers do not share one contract for visibility,
selection, or the processor Preview badge.
The canvas classifies visible, entering, and leaving components in
updateCanvasVisibility, then each layer calls Renderer.pan() to refresh only
those components. Click and double-click handlers are often attached only when
canSelect is already true at render time, so a later editing change does not
affect an existing element until something renders it again. The processor
Preview badge is decided inside ProcessorRenderer.isPreviewProcessor during
update, while ProcessorUiState.preview is left unset.
Upcoming troubleshooting work enables canvas editing on an already mounted
canvas, builds context menus and an operation panel from the current selection,
and aligns components from their visual bounds. Those features need one place
to classify visibility, one place to read canSelect and canEdit, and one
stamped preview flag.
h2. Goals
* Classify visibility inside each renderer during its normal update.
* Attach pointer handlers once and read canSelect and canEdit when the event
fires.
* Stamp ui.preview where processor data is produced, and have the processor
renderer read that flag.
* Preserve the current rendered appearance and interaction results.
* Leave troubleshooting features to their existing tickets.
h2. Scope
h3. Visibility
* Move viewport classification out of CanvasComponent.updateCanvasVisibility
and into each renderer update.
* Apply this to the funnel, label, port, processor, process-group,
remote-process-group, and connection renderers.
* Remove Renderer.pan() and the layer pan() methods that exist only to refresh
entering and leaving components.
* Keep off-screen components from drawing their details, and keep entering and
leaving transitions.
h3. Selection and edit gating
* Attach click and double-click handlers when an element enters, including
connection bend and endpoint handlers.
* Read getCanSelect() and getCanEdit() inside the handler.
* Do not skip attaching a handler because canSelect was false on the render
that created the element.
* Keep drag behavior on the same fire-time gate.
h3. Preview badge
* Stamp ui.preview when processors are mapped and when a same-id processor
refresh arrives.
* Stamp the same flag on processor selection targets so an operation panel can
read it without joining canvas wrappers.
* Match a readable processor whose type and bundle group, artifact, and version
are in the Preview-tagged extension list.
* Change the processor renderer to show the badge only when ui.preview is true.
* Remove the render-time preview lookup.
h2. Out of Scope
* Adding troubleshooting commands, banners, route guards, alignment, provenance
replay, or Controller Service editing.
* Migrating the legacy flow-designer canvas.
* Changing REST payloads or rendered appearance.
* Rewriting connection bend and endpoint behavior beyond the shared handler and
gating contract.
h2. Acceptance Criteria
* No renderer exposes pan(), and the canvas no longer classifies visibility for
the renderers.
* Each renderer sets visible, entering, and leaving during its own update.
* A canSelect or canEdit change takes effect on the next event without waiting
for handlers to be reattached.
* The processor renderer reads ui.preview and does not match the extension list
itself.
* The same preview match feeds the canvas wrapper and the processor selection
target.
* Off-screen detail suppression, badge placement, and selection behavior remain
unchanged.
* Frontend lint, unit tests, and the reusable-canvas specs pass.
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