The purpose of enter_*() and exit_*() is to control what happens with data that does not persist during a tween. In general the non-persistent data is transformed to an invisible version that can be tweened to, e.g. by setting the opacity to 0 or be moving the element off-screen. It is possible to define your own transformations, or rely on some of the build in effects.

enter_manual(default = NULL, ..., name = "manual")

enter_appear(early = FALSE, ...)

enter_grow(..., size = 0)

enter_recolour(..., colour = "white", fill = colour)

enter_recolor(..., color = "white", fill = color)

enter_fly(..., x_loc = NA, y_loc = NA)

enter_drift(..., x_mod = 0, y_mod = 0)

enter_reset()

exit_manual(default = NULL, ..., name = "manual")

exit_disappear(early = FALSE, ...)

exit_shrink(..., size = 0)

exit_recolour(..., colour = "white", fill = colour)

exit_recolor(..., color = "white", fill = color)

exit_fly(..., x_loc = NA, y_loc = NA)

exit_drift(..., x_mod = 0, y_mod = 0)

exit_reset()

## Arguments

default

A default transformation to use

...

Additional specific transformations either named by the geom (e.g. bar, or by its position in the layer stack, e.g. "2")

name

A name for the manual modification (only used when printing the object)

early

Should the data appear in the beginning of the transition or in the end

alpha

The start/end transparency.

size

The proportional start/end size. 0 means complete shrinking while 1 means no shrinking

colour, color, fill

The start/end colour and fill the elements should (dis)appear into

x_loc, y_loc

Start and end positions of the graphic elements

x_mod, y_mod

Modification to add to the entering or exiting data

## User-defined transformations

All enter/exit functions allows the user to add additional transformation functions targeting specific layers. If the functions are named, then the name is understood to reference the class of geoms it applies to. If the functions are unnamed or numbered they will apply to the layer with a matching index in the stack. Named and indexed transformations cannot be mixed.

All modifications except enter_manual()/exit_manual() sets a range of modifications already, but further can be added with the .... For the manual versions a default transformation can be set which will apply to all layers that does not match any of the other given transformations. Often a single default transformation is enough and no specific transformations are needed.

Transformation can be given as any expression that can be converted with rlang::as_function(). This means that purrr style lambda functions are allowed in addition to anonymous functions etc. Transformation functions must accept a data.frame and return a data.frame of the same dimensions. The function will be called with the entering/exiting layer data, except for the case of polygon- and path-like layers in which case the function recieves the entering/exiting polygon/path data one by one. A special option is to set a transformation as NULL instead of a function. In that case the entering and exiting data will simply appear/disappear when it is no longer part of a frame.

## Modification composition

Enter and exit modifications are composable so that multiple different ones can be added to an animation and will be applied in turn. You can also combine multiples and save them as a new enter or exit modification using c().

Due to the composable nature of enter and exit modifications it is not possible to overwrite a prior modification by adding a new. If it is needed to start from scratch then the sentinels enter_reset() and exit_reset() are provided which clears all prior modifications.

## Modification types

A range of modification types are provided by gganimate and using enter_manual()/exit_manual() or modification composition it is possible to create your own.

appear/disappear will simply make elements appear/disappear at either the start or end of the transition. The default if nothing else is added.

fade will simply set the alpha value to zero making the elements fade in/out during the transition.

grow/shrink will set the elements to zero size making them gradually grow into / shrink out of existence. Zero size depends on the type of layer, e.g. polygons/paths will have all their points set to the mean, while points will have size/stroke set to zero.

recolour/recolor will change the colour and/or fill of the elements making them gradually change from the defined colour and into their try colour. Be aware that unless the colour and fill are set to the same as the background colour of the plot this modification needs to be combined with others to ensure that elements does not abruptly appear.

fly will set a specific x and y position where all elements will enter from/ exit to, irrespectible of their real position.

drift will modify the real position of the entering and exiting elements by a specified amount, e.g. setting x_mod = -5 will let all elements enter from/exit to the left with a terminal position 5 points to the left of the real position.

## Examples

# Default is appear/disappear
anim <- ggplot(mtcars, aes(factor(gear), mpg)) +
geom_boxplot() +
transition_states(gear, 2, 1)