6 Pict Rebuilds🔗ℹ

To support Pict.rebuild, the representation of a pict effectively records all primitive operations used to construct the pict. This recording is limited to Pict and Find objects. If, for example, you use Find.in to obtain a number and then construct a pict using that number, the number itself cannot record its derivation from the picts used with Find.in. In such cases, use rebuildable or the ~children argument of animate to establish a connection between the input picts and the result.

When traversing the children of pict to rebuild it, the pre_adjust function is applied to each pict before its own children. When pre_adjust returns a value other than the pict that it is given, rebuilding does not recur to its children, and the result of pre_adjust is used immediately as the rebuilt replacement for the given pict. When rebuilding does recur, when a pict’s descendants are unchanged and when config_adjust (if applicable) returns a configuration unchanged, then the original construction of the pict is kept. Finally, post_adjust is applied to either the rebuilt pict or so-far-preserved original pict to obtain the rebuilt replacement for the original pict. The replacement of a given pict is cached, so pre_adjust and post_adjust are each applied at most once to a pict within a call to Pict.rebuild.

A rebuilt pict–either pict itself or a rebuilt dependency—shares the identity of the original pict, so the rebuilt pict can be located via Find objects, replaced via Pict.replace, or extracted using Pict.find_rebuilt. See also Pict Findable and Replaceable Identity.

> def s = square(~size: 20, ~fill: "blue")

> def p = beside(~sep: 10, s, Pict.launder(s))

> p

> p.rebuild(~pre: fun (q): if q == s | s.scale(2) | q)

> p.rebuild(~pre: fun (q): if q == s | s.scale(2) | q,             ~post: fun (q :~ Pict):                      rectangle(~around: q.pad(2), ~line: "red"))

This operation is equivalent to a use of Pict.rebuild:

pict.rebuild(~pre: fun (p):

if p == orig

| replacement

| p)

> def s = square(~size: 20, ~fill: "blue")

> def c = circle(~size: 15, ~fill: "red")

> def p = beside(~sep: 10, s, s)

> p

> p.replace(s, c)

This operation is equivalent to a use of Pict.rebuild:

pict.rebuild(~configure:

fun (config :: Map):

if config.has_key(key)

| config ++ { key: val }

| config)

See "identity" for more information about pict identity and rebuilt picts.

The given deps list determines the replaceable dependencies of the result pict, but the result from proc determines the findable children.