User-settings for mapcss mappaint styles

[bastiK]

We could allow the user to customize the rendering of a style in a more user friendly way. There would be one or more additional entries in the right click menu of the style (in the mappaint toggle dialog). This entry would bring up a new window, where settings can be customized, or a simple boolean value could be done in a submenu entry.

We'd also need a language to specify and use these settings in the mapcss style. Here is a draft:

/* simple boolean value yes/no */
setting::highway_casing {
  type: boolean;
  label: tr("Show highway casing");
  default: false;
}

/* a list of options where exactly one option is selected */
setting::zoom_behavior {
  type: list_selection;
  label: tr("Zoom");
  option-keys: list(zoom_auto, zoom_show_all);
  option-labels: list(tr("Auto (hide icons at low zoom)"), tr("Fixed (show all icons and labels)"));
  default: auto_zoom;
}

/* a color value */
setting::motorway_color {
  type: color;
  label: tr("Motorway");
  default: #809bc0;
}

/* float, int, ... */

/* show casing if setting is true */
way.highway_casing[highway] {
  casing-width: 1;
  casing-color: gray;
}

/* hide nodes at z0-15 if zoom is auto */
node|z-16.zoom_auto {
  icon-image: none;
}

/* show motorway with corresponding color */
way[highway=motorway] {
  width: 3;
  color: prop("motorway_color");
}