A finished notan shows only where every piece ended up. Replay shows how they got there: it plays the flip of every cut again, one after another, in the order you made them. It is a way of looking, not of editing, and it changes nothing.
What it does
The ▶ button sits beside the zoom control. Press it and each cut, oldest first, turns over at its edge and travels to where its piece lies, and then the next begins. Each fold takes a little over half a second and a new one starts every 0.78 seconds, so a design of ten cuts plays in about eight. A short message counts them: ‘Playing 10 flips.’ Shapes that put paper back play too, their paper arriving instead of leaving.
The button is dimmed when there are no cuts, and when there are, its tooltip counts them: ‘Play the flips again (4 cuts, in the order they were made)’. Pressing it while a replay is running does nothing. If the view is still framing the design by itself, it makes room for the pieces as they fly, as it does for a new cut. If your system is set to reduce motion, each fold happens at once instead of turning, still one cut after another.
Replay plays the design as it is now, not a recording of how you made it. Each cut folds with its present shape, over its present edge, from where it sits now. A cut you moved plays from its new place; a cut you undid or deleted does not play at all; colors you tried and abandoned are not there. The one thing it keeps from the past is the order in which the cuts were first made, which the app remembers because it decides whose paper each later cut takes. A cut with no paper left to show is skipped.
Nothing about the design changes. A replay adds no undo step and is not saved. The flying paper is a throwaway copy, so an undo or a reset in the middle of a replay simply drops it.
Why it works this way
A notan is a sequence of folds, and the finished sheet shows only the last state of that sequence. Watching the cuts go over in order is how you check that the arrangement reads as one gesture, and it is the only way to see a cut that later cuts have buried: a piece folded out and then covered by another, or a hole later filled.
It sits with the zoom control rather than in the title bar because it is a way of looking at the sheet, not of changing it, and the title bar already carries the controls that change things. It is dimmed when there is nothing to play, and refuses to start a second replay over the first, so it cannot tangle itself.
The animation always runs after the design has changed, on a copy of the paper. That is why a replay can be abandoned at any frame without leaving the design half-folded, and why it can never alter what it shows.
The metaphor
The metaphor is the flip book: a stack of drawings that, riffled under the thumb, becomes movement. Replay is the flip book of your design’s folds, one page for each cut.
It breaks in an instructive way. A flip book plays exactly the drawings its maker drew. Replay rebuilds its pages from the finished design, the way you might work out from a finished origami model the order its folds must have gone in. It is the recipe read back from the finished dish, not a film of the cooking.
A history
In art
Japanese handscrolls, emakimono, were made to be read a section at a time, unrolled from right to left, so that a story unfolds in time under the reader’s hands. Paper folding found its own way to show a sequence. In 1954 Akira Yoshizawa published a notation for origami: dashed lines for valley folds, dash-and-dot lines for mountain folds, and arrows for the movement of the paper, one drawing for each step. Samuel Randlett and Robert Harbin took it up, and by the early 1960s it was the standard way to diagram a model, fold by fold, in order.
In The Mystery of Picasso, released in 1956, the director Henri-Georges Clouzot filmed Pablo Picasso at work. Picasso drew with inks that bled through the paper while the camera watched from the other side, and later paintings were filmed stage by stage, so that images appeared, changed and were painted over in front of the audience. The film showed what the finished pictures could not: the ones buried underneath.
In printing
Color printing has a replay of its own, the set of progressive proofs. Progressives show each color plate printed alone and then in combination, in the order the inks go on the press: one color, then two together, then three, then all. They let a printer see how each layer changes what lies beneath it, which is the question the order of a notan’s cuts answers. A Japanese color woodblock print is built the same way, block after block, each color laid over the ones before.
In technology
Machines for replaying a sequence of pictures came before cinema. Joseph Plateau’s phenakistiscope, in the early 1830s, spun a disc of drawings behind slits. William George Horner described a drum version in 1834, which William E. Lincoln patented in the United States in 1867 and named the zoetrope. John Barnes Linnett patented the flip book, as the kineograph, in 1868. Eadweard Muybridge’s photographs of a horse in motion, published in 1878, were soon mounted in zoetropes, some by Muybridge himself. Television made replay immediate: on 7 December 1963, during the Army–Navy football game, the CBS director Tony Verna played a moment of the game back on videotape almost as soon as it had happened.
Software can replay work too. A program can keep a document as the list of changes that made it and play them back in order. Replay here does something simpler and more faithful to the paper: it asks the finished design for its cuts, sorts them by the order they were made, and folds each one again.
In professional software
Programs that replay work do it in one of two ways. Some record every stroke and play the recording back as a time-lapse. Others rebuild the finished design step by step from its present parts, as Replay does here. Knowing which you are watching tells you what it can show.
- Procreate. Each canvas records a time-lapse as you draw, while ‘Time-lapse Recording’ is on. ‘Time-lapse Replay’, under ‘Actions › Video’, plays it back on the canvas, and the same menu exports it as a video, at full length or cut to 30 seconds. It shows everything, including the strokes you later erased.
- Adobe Fresco. Fresco also records your strokes as you paint, and its Share menu exports the recording as a time-lapse video. Like Procreate’s, it is a film of the work, not a rebuild of it.
- Autodesk Fusion (formerly Fusion 360). The timeline along the bottom of a parametric design has play and step buttons at its left. Press play and the marker walks through the features in order, rebuilding the model one step at a time. It is the closest relative of Replay: each step plays in its present form, in its place in the sequence.
- Adobe Photoshop. The History panel is a list of recent steps rather than a film. Click back through it to see the image at each state, then click the last state to return. It holds only recent steps, and it is gone when you close the file.
What carries over. A replay is for reading a design, not changing it: watch one to see the order of the work and what later steps have hidden. The difference to remember is that a time-lapse shows what happened, mistakes and all, while a rebuild shows only what survives.
Try this
- Make four cuts, one over each edge, and press ▶.
- Cut a large shape over several earlier ones, then replay to see the pieces it buried.
- Move one of your first cuts to the other side of the sheet and replay: it still plays first, from its new place.
Going further
Read on with Zoom, Flipping and Undo and redo.
- Frank Thomas and Ollie Johnston, The Illusion of Life
- Samuel Randlett, The Art of Origami