All of Asymptote’s graphical capabilities are based on four primitive
commands. The three PostScript drawing commands draw,
fill, and clip add objects to a picture in the order in
which they are executed, with the most recently drawn object appearing on top.
The labeling command label can be used to add text
labels and external EPS images, which will appear on top of the
PostScript objects (since this is normally what one wants), but
again in the relative order in which they were executed. After drawing
objects on a picture, the picture can be output with the
shipout function (see shipout).
If you wish to draw PostScript objects on top of labels (or verbatim
tex commands; see tex), the layer command may be
used to start a
new PostScript/LaTeX layer:
void layer(picture pic=currentpicture);
The layer function gives one full control over the order in which
objects are drawn. Layers are drawn sequentially, with the most recent
layer appearing on top. Within each layer, labels, images, and
verbatim tex commands are always drawn after the
PostScript objects in that layer.
A page break can be generated with the command
void newpage(picture pic=currentpicture);
While some of these drawing commands take many options, they all have sensible default values (for example, the picture argument defaults to currentpicture).