See https://github.com/qgis/QGIS-Enhancement-Proposals/issues/299
Implements the API framework for setting advanced labeling engine
rules for a project, and implements 4 initial rule types:
- QgsLabelingEngineRuleMinimumDistanceLabelToFeature: prevents labels
being placed too *close* to features from a different layer
- QgsLabelingEngineRuleMaximumDistanceLabelToFeature: prevents labels
being placed too *far* from features from a different layer
- QgsLabelingEngineRuleMinimumDistanceLabelToLabel: prevents labels
being placed too close to labels from a different layer
- QgsLabelingEngineRuleAvoidLabelOverlapWithFeature: prevents labels
being placed overlapping features from a different layer
(note that the first 3 rules require a build based on GEOS >= 3.10,
they are not available for older GEOS builds)
Also implements a registry for storing available rule classes,
and serialization of rules and configuration in QGIS projects
For the "Around point" and "Cartographic" placement modes, this
adds a new optional setting for the maximum distance of the labels from
the feature. It's used together with the existing distance setting
to define a range of distances at which labels may be placed
from their corresponding point features.
This adds more flexibility to the placement for these layers,
ultimately allowing for more labels to be placed in busy maps.
When the layer is set to the "around point" mode, then label
candidates which are closer to the point will always be prefered
over those which are further away.
When the layer is set to the "cartographic" mode, then the default
behavior is also to prioritize closer labels. A new combo box
allows users to control the priority, with an option for
prefering position ordering. If this option is set, then candidates
at the corresponding positions (eg top left) are preferred regardless
of how far they are from the point, with the labelling falling
back to alternate positions only when no labels can be placed
up to the maximum label distance.
Sponsored by Rubicon Concierge Real Estate Services
The old sip based approach to handling property -> getter/setter
conversion is broken on sip6, so move the patching into Python.
Also fix incorrect checks in tests, and add additional test
for compatiblity code.
Shows the text bounds of the label in red and baselines in blue.
Designed for debugging purposes only.
Also move label engine enums to Qgis, promote to enum class
- Move settings to be feature level, not layer level, and permit
data defined control of these settings
- Add additional option for overlap handling for "Always allow"
overlaps, which indicates that the user doesn't care at all
if the label overlaps other labels and that the ideal placement
should always be used for the label regardless of whether it
overlaps labels or not
To clarify further, the options are:
- Never Overlap : never ever place overlapping labels for the layer,
even if it means labels will be missing
- Allow Overls if Required: if the label can't otherwise be placed,
draw an overlapping label. This mode will cause the label to be moved
a less ideal placement if possible, e.g. moving the label further
from the center of a line or polygon, IF doing so will avoid overlapping
labels. But if there's no other positions possible, then draw the
label overlapping.
- Always Allow Overlaps": It doesn't matter at all if the label
overlaps other labels or obstacles, that's fine to do and the best
placement (e.g most central placement) should always be used even if an
alternate further placement is possible which avoids overlaps entirely.
two separate new options
This setting was ambiguous in meaning -- it could be interpreted
as either:
"I don't care about overlapping labels, use them when
you have no other choice"
OR
"I want to see labels for EVERYTHING in this layer, and I don't
care what you have to do to show me those"
This leads to situations like those discussed in #41043, where some
users interpret the setting as the first meaning and get confused
when eg. a curved label line layer starts showing horizontal placements
for some features which couldn't otherwise be labeled (eg short
lines).
So, split the setting into two new options (checkboxes) with explicit, clear
distinction:
- "Allow overlapping labels if unavoidable": This setting means labels
can be overlapping, if there's no other option. It does NOT gaurantee
that all features in the layer will have labels, because other
constraints (such as lines too short to fit a label's text) will still
be respected and may prevent labels for the feature.
- "Allow inferior fallback placements": This mode permits features
to fallback to worse placement options when there's no other choice,
e.g. when a line is too short to fit a curved label text then the
label may be placed horizontally just over the feature's center
point.
The combination of checking BOTH options WILL gaurantee that
all features in the layer are labelled, albeit with both overlapping
labels and the degraded placements!
Fixes#41043
means when the line anchor is < 25% then it will be matched to the
start of the text, when the line anchor is > 75% it will be matched
to the end of the text, otherwise match to center of text
middle or end) of line labels corresponds to the anchor position
Previously labels would always be centered over the anchor position
of lines (unless it was a curved label, in which case it was the
start of the lable!) This is limiting (and inconsistent) for some
placements, where it is preferable to e.g. line up the end
of the label text with a specific point on the line
