The single seam between the grammar and the renderers. Each geom method
returns a list of marks; a mark is a plain named list with a type field
(currently "circle"; the full catalog will add "rect", "line",
"path", "polygon", "text") plus type-specific fields in normalized
panel coordinates (x/y in [0, 1], y pointing up). Because both render
targets consume marks, adding a geom never touches renderer code, and
adding a renderer never touches geom code.
build_marks(geom, ...)A Geom subclass instance.
Method arguments; all methods take scaled, a named list of
scaled aesthetic vectors (x, y in [0, 1]; color as hex;
size as radius in px; alpha in [0, 1]).
List of marks.