typedef int PK_render_vis_t;
This data type is used to determine whether any visibility evaluation
is to be performed. It has the values:
PK_render_vis_no_c no visibility evaluated (default)
PK_render_vis_hid_c don't output hidden lines
PK_render_vis_inv_c output hidden lines marked as invisible
PK_render_vis_inv_draft_c output hidden lines and distinguish between
those hidden by other lines and those
hidden by faces.
PK_render_vis_extended_c visibility is evaluated. The information
output is controlled by the invisible,
drafting and self_hidden options of
the PK_TOPOL_render_line_o_t structure.
