Adds a ProjectUsageTracker (sources/project/) that accumulates how
long a project has been the active tab, using QElapsedTimer so the
value is computed on demand rather than via polling. It's hosted on
ProjectPropertiesHandler per that class's own stated design intent
("all new properties should be managed by this class").
The accumulated time is persisted as a new <usage time_spent="N"
enabled="true|false"/> element, a sibling of <properties> in the
project XML, written/read by new QETProject::writeUsageXml()/
readUsageXml(). It rides along on the existing autosave path for
free, since writeBackup() already serializes the full project via
toXml().
QETDiagramEditor::subWindowActivated() now pauses every open
project's tracker except the one whose tab just became current, so
switching between several open projects keeps each project's tracked
time isolated.
Surfaced in the existing Project Properties "Général" page: a
"Temps passé sur ce projet" display, a "Réinitialiser" button, and
an opt-out checkbox ("uniquement enregistré localement dans ce
fichier" - this is local-only, never transmitted anywhere).
Verified beyond compiling: full CMake build, then an actual runtime
session confirming the saved XML's time_spent value, that closing
and reopening the project round-trips and resumes timing, that the
reset button works, and - the key correctness check - that with two
projects open, the inactive one's time_spent stays frozen while the
active one accumulates real elapsed time, over the same interval.
See discussion #576.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
QHash/QMap::keys() allocates a list of every key on each call, then
contains() searches it linearly - an accidental O(n) plus allocation
where a direct O(1) lookup was meant. 35 occurrences across 7 files,
found while profiling project load times (context: #553/#560).
The hot one is ElementPictureFactory::getPictures(), which runs once
per element instance on project load: on the 3399 KiB example project
(191 instances, 129 cache hits) the keys() detour cost 45 ms of the
1.34 s total - measured, not estimated; the fix reproducibly shaves
~35-45 ms off that load. The remaining call sites are UI paths
(search&replace, dynamic text model, undo commands) where the waste
scales with selection/model size.
No behavior change: for QHash/QMap, keys().contains(k) and
contains(k) are equivalent by definition.
(cherry picked from commit 0a7f8f072fa68de7c01a9fc134a4bc8e16d62062)
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