Halo outline rendering

In addition to the Outline styling options that are available for all generic draw objects, you can enable a global "halo outline" which will be rendered around all included draw objects, including tactical graphics with advanced line textures.

This can be enabled through styling:

      <compositeitem name="Line">
        <valueitem name="DrawHaloOutline" value="true" />
      </compositeitem>

or through the **DrawHaloOutline** data field.

The color and thickness of this outline is controlled by the following properties in the IMariaDrawObjectLayer interface:

        /// <summary>
        /// Shared outline color used for draw objects whose Line.DrawHaloOutline styling is enabled.
        /// </summary>
        Color HaloOutlineColor { get; set; }

        /// <summary>
        /// Shared outline thickness in logical pixels. Note that high values here
        /// might cause performance issues. Default: 3.0
        /// </summary>
        double HaloOutlineThickness { get; set; }

The purpose of this feature is mainly to improve visibility and readability of tactical graphics. For styling of individual objects, see the Outline styling options of the Line Styling documentation.