Add a "show canvas boundary" display option, and a corresponding
"View" menu item and default-apperance preferences option. When
enabled (the default), the canvas boundary is shown as an orange/
black dashed line in "show all" mode.
Pass the display scroll offset down to gimp_cairo_stipple_pattern_create()
and set it as offset on the created cairo pattern, so stipple patterns
look the same no matter how the display is scrolled.
With gimp_guide_custom_new(), you can create a custom guide with a different
style on canvas (other pattern/color/width). A custom guide won't be saved
and could be used, for instance, for specific GEGL op guiding.
Ell