Date 2025-11-18
Author Nyall Dawson (@nyalldawson)
Contact nyall dot dawson at gmail dot com
Version QGIS 4.0
Current QGIS versions offer a "curved" label placement mode for placing label text with regular spacing along a line/curve geometry.
There are current limited options for controlling how the characters are placed for a curved label. Choices are limited to a fixed value for the character spacing and for word spacing.
This QEP introduces additional placement "modes" for use with curved labels, allowing for much more fine-grained control over how text is positioned for curved labels.
These additional modes will be exposed as options which are visible and enabled whenever a line geometry type layer is set to curved label placement. (Note that while curved labeling is available also for polygon perimeters, the new modes only make sense for line geometry types and consequentially will not be exposed when a polygon layer is active).
A data defined override will be available for the new curved placement modes, allowing mixed use of different modes for features within a single layer.
The modes to be introduced are:
Existing behavior, no change. Glyphs will be placed at regular character and word spacing along the curved line geometry.
When this mode is selected, each individual character from the label text will be placed such that their left-baseline position is located at a corresponding vertex from the curved line geometry. I.e. the first character will be placed at the start of the line, the second at the second vertex, the third at the third vertex, etc.
If the curved line geometry does not contain sufficient vertices for the characters present in the label text then the excess characters will be ignored and will not be rendered.
If the label’s “distance” setting is non-zero, then the character will be vertically offset from the vertex position by this distance.
Characters will be rotated to follow the line angle at the vertex.
When selected, this mode will increase (or decrease) the character spacing used for each label in order to fit the entire text over the actual length of the curved line geometry.
When selected, this mode will increase (or decrease) the word spacing used for each label in order to fit the entire text over the actual length of the curved line geometry.
The new placement modes will be introduced as a enum, Qgis::CurvedLabelMode. The enum will be exposed via the
existing QgsLabelLineSettings class.
It will default to the Default value, ensuring that the placement for existing projects will remain unchanged.
Internally, the pal FeaturePart::createCurvedCandidatesAlongLine function will be modified to respect the curved
label mode when generating the placement of characters for a particular feature.
None
None, this is a new setting and the default behavior will remain unchanged.
N/A - the new modes will only be available in QGIS 4.0+.