# How to contribute styles

You can contribute style changes without editing any Python code using the
following process:

* Download (or build) and open the most recent version of the project in QGIS.
* In the 'Layers' menu, double click on the layer you wish to edit.
* Open the 'Symbology' tab.
* Make your desired style changes.
* In the lower-left corner, click the 'Style' dropdown.
* In this menu, select 'Save Style...'

![Save style](/_images/save_style.png)

* At this point, if you are uncomfortable with Git and GitHub, you can email us
  your style file at qgreenland.info@gmail.com. Otherwise, continue on...
* Save the style to `qgreenland/assets/styles/<name>.qml` directory of this
  repository or your fork. Keep in mind that styles can be shared between
  layers, so give the style a generic name instead of a layer-specific name
  where possible.
* Edit the relevant layer configuration file in `qgreenland/config/layers` and
  find the layer(s) you wish to apply this style to. Populate the `style`
  attribute for each layer with the name of the `.qml` file you saved in the
  previous step, excluding the file extension. For example, if you saved
  `foo.qml`, then populate `style='foo'`.


## Continuous colormap considerations

Continuous colormaps, since QGIS 3.18, support displaying a gradient legend.

A colormap is continuous if its interpolation mode is set to "Linear" (in the QML, the
value is `"INTERPOLATE"`).

!["Linear" interpolation selected in the QGIS symbology
menu](/_images/qgis_symbology_linear_interpolation.png)

These continuous legends will not display the units we populated in the "Label unit suffix"
field for QGreenland v2, so some extra effort has to be taken to display them in the new
continuous legend. In the "Legend Settings" menu, ensure:

* Any units are populated in the "Suffix" field
* "Orientation" is set to "Horizontal"

![QGIS "Legend Settings" menu with "Suffix" set to "m/s" and "Orientation" set to
"Horizontal"](/_images/qgis_symbology_legend_settings.png)


## Troubleshooting

### Layers using my style are displaying font warnings in QGIS on some operating systems

e.g. `Font "Helvetica" font not available on system`.

See [this GitHub issue](https://github.com/nsidc/qgreenland/issues/515) for more. For
example it is possible your style `qml` file contains `fontFamily="Sans Serif"` and
that is being automatically converted by PyQGIS to a value like `Helvetica` (a
proprietary font) when writing the final project file. Try `fontFamily="Open Sans"`
instead!