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This change introduces a metric-based implementation of the
Ramer-Douglas-Peucker line simplification algorithm to generate a
LOD pyramid for the polyline geometries.
This comes with a related property (in MapItemBase), lodThreshold,
that can be used to change the threshold after which no simplification
will be used.
By default the value of this property is 0, meaning that the
behavior will be unchanged and no LOD will be used.
This change also introduces LOD on map polyine objects QSG, for which
no property is introduced, and there's a default threshold set to
zoom level 12 (which appear to produce acceptable results).
Finally, this patch makes use of a threadpool with 1 thread
to enqueue geometry simplification tasks, which would otherwise
freeze the UI when computing for the first time.
Support for geometry simplification is currently added only to polylines.
It might be of interest extending it to polygons as well, once
a proper strategy for handling the simplification of inner holes has
been identified.
Finally, extending it to circles could be of interest, while potentially
bringing only minor benefits, as circle geometries are currently fixed
to 128 vertices.
Also adds a MapObject-based delegate to the geojson viewer example.
Task-number: QTBUG-46652
Task-number: QTBUG-38459
Task-number: QTBUG-49303
Change-Id: I64b5db4577962db17e5388812909285c9356ef0d
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
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This patch changes the implementation of the scenegraph-based
mapobjects (those created by QGeoTiledMap) to be the recently
introduced one sporting shader-based map projection.
This is much faster than the previous, but may introduce small glitches
at this time (mostly on minified polylines).
Adding polyline LOD simplification will solve this problem.
Compared to equivalent Map Items (that is, Map Items backed by the
same underlying implementation), map objects now are approximately
1.5x faster.
This measure has been gathered using medium-size polygons (contained
in the file 10_countries.json from the geojson_viewer example).
The difference is caused by the additional QtQuick geometry related
operations (essentially projecting the bounding box for each item)
present in MapItems.
Smaller polygons may therefore yield larger improvements, larger polygons
the opposite.
Change-Id: I3fc92b02b74a3a4d001e69755949a98f80d8a3d3
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>
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With this change, all the geo-to-screen conversion,
and the triangulation operations for geo polylines
and geo polygon are performed either at set time
or in the shader.
A separate bounding box geometry is processed
in the old way to provide a correct QtQuick Item
geometry, that can be used for nesting mouse areas,
performing translations, input event delivery, etc.
With this approach, performance are improved by more
than one order of magnitude in average, but complex
geometries will of course benefit more.
It also adds correct rendering support for polygons
with holes, previously only rendered correctly
by the MapboxGL plugin.
The polyline shader has basic miter joins. The miter is
skipped if the angle is too sharp to avoid complicating
the implementation.
This shader introduces some glitches when the polyline
is minified, for which the real fix is to
have LOD for the geometry, and render simplified
geometries at low zoom levels (added in a subsequent patch).
Note: this approach, at least in its current implementation,
does not support enabling layers on individual items, only
on the Map element.
Task-number: QTBUG-49303
Task-number: QTBUG-38459
Change-Id: I0c2dc0bf364d32f74ca7c4014f6d66e6219c8ae4
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
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