Informs Pango that the way that the rendering is done for part has changed.
This should be called if the rendering changes in a way that would prevent multiple pieces being joined together into one drawing call. For instance, if a subclass of `PangoRenderer` was to add a stipple option for drawing underlines, it needs to call
``` pango_renderer_part_changed (render, PANGO_RENDER_PART_UNDERLINE); ```
When the stipple changes or underlines with different stipples might be joined together. Pango automatically calls this for changes to colors. (See [[email protected]_color])
| this |
a `PangoRenderer` |
| part |
the part for which rendering has changed. |