Previously, when marker or hash lines were rendered using interval
or center point place placement, the symbol angles were determined
by taking the exact line orientation at the position of the symbol.
This often leads to undesirable rendering effects, where little
jaggies or corners in lines which occur at the position of the
symbol cause the marker or hash line to be oriented at a very
different angle to what the eye expects to see.
With this new option, the angle is instead calculated by averaging
the line over a specified distance either side of the symbol. E.g.
averaging the line angle over 4mm means we take the points along
the line 2mm from either side of the symbol placement, and use these
instead to calculate the line angle for that symbol. This has the
effect of smoothing (or removing) any tiny local deviations from
the overall line direction, resulting in much nicer visual
orientation of marker or hash lines.
Like all symbol settings, the average angle smoothing distance
can be set using mm/pixels/map units/etc, and supports data-defined
values.
Closed rings also correctly consider wrapping around these average
angles from the start/end vertex.
(Sponsored by an anonymous corporate backer)
This line symbol type is designed to replicate the ArcGIS Hash Line
symbol layer type. It allows for a repeating line segment to be
drawn over the length of a feature, with a line-sub symbol used
to render each individual segment.
To reduce code duplication, this is heavily based off the current
line marker symbol layer, since the functionality is almost
identical (draw some sub symbol at some interval along a line).
Accordingly, I've split off QgsMarkerLineSymbolLayer to move
as much of the common functionality as possible to a new abstract
base class, so that only the actual marker/line segment rendering
occurs in the marker line/hash line subclasses.
This also gives the hash line all the existing placement options
permissible for marker lines -- e.g. first/last vertex, mid points,
regular intervals, etc.
The hash line length and angle can have data defined overrides,
which are evaluated per-line segment, allowing for the hash line
to change size and angle over the length of a single rendered
feature.
render exterior ring or interior rings
This option is shown whenever a simple line symbol or
marker line symbol is used as part of a fill symbol for
rendering polygons.
The default behavior is to render both interior and exterior
rings, but this new setting allows users to set the symbol
layer to render only for the exterior ring OR only
for interior rings.
This allows for symbolisation which wasn't directly possible
before, such as a marker line with markers for interior
rings angled toward the interior of the polygon.
Sponsored by the German QGIS User Group
Fixes#12652
