Undo/redo history for dragmapr states — d

d_history() creates an undo/redo stack for dragmapr_state objects. Push a checkpoint with d_history_push() after each meaningful edit, then step backwards with d_undo() and forwards with d_redo(). Pushing a new checkpoint clears the redo stack, matching familiar editor behaviour.

Usage

d_history()

d_history_push(history, state)

d_undo(history)

d_redo(history)

Arguments

history: A dragmapr_history object created by d_history().
state: A dragmapr_state checkpoint to remember.

Value

d_history() returns a dragmapr_history object; d_history_push() returns the history invisibly; d_undo() and d_redo() return the restored dragmapr_state.

Details

The history object has reference semantics: d_history_push(), d_undo(), and d_redo() modify it in place, so reassignment is optional.

Examples

h <- d_history()
s0 <- d_state(
  region_offsets = data.frame(region = "A", dx_m = 0, dy_m = 0)
)
d_history_push(h, s0)
s1 <- d_nudge(s0, "A", dx_m = 50)
d_history_push(h, s1)
back <- d_undo(h) # s0 offsets again
fwd <- d_redo(h)  # s1 offsets again
d_state_equal(back, s0)
#> [1] TRUE
d_state_equal(fwd, s1)
#> [1] TRUE