# Screens and Python

Ren’Py supports defining screens in Python, as well as in the Ren’Py screen language. A Python screen is created by supplying a screen function to the `renpy.define_screen()` function. It can then be used like it was any other screen.

The screen function should have parameters corresponding to the scope variables it expects, and it should ignore extra keyword arguments. (That is, it should have **kwargs at the end of its parameter list.) It is then expected to call the UI functions to add displayables to the screen.The screen function is called whenever an interaction starts or restarts.

To ensure that this restarting is seamless to the user (and not causing things to reset), it’s important that every call to a UI function supply the id argument. As a screen is re-created, Ren’Py will update each displayable with the contents of the old displayable with the same id. Ids are generated automatically by the screen language, but when doing things by hand, they must be manually specified.

Warning

UI Functions are deprecated and not recommended.

Here’s an example Python screen:

    init python:
        def say_screen(who, what, **kwargs):
            ui.window(id="window")
            ui.vbox(id="say_vbox")

            ui.text(who, id="who")
            ui.text(what, id="what")

            ui.close()

        renpy.define_screen("say", say_screen)

## Screen Functions

The following functions support the definition, display, and hiding of screens.

## UI Functions

Note

The implementation of Ren’Py has changed, and UI functions that create displayables can now be far slower than their screen language equivalents.

The UI functions are Python equivalents of the screen language statements. For each screen language statement, there is a ui function with the same name. For example, ui.text corresponds to the text statement, and ui.add corresponds to the add statement.

There is a simple mapping between screen language parameters and arguments and Python arguments. Screen language parameters become positional arguments, while properties become keyword arguments. For example, the screen language statement:

    text "Hello, World" size 40 xalign 0.5

becomes:

    ui.text("Hello, World", size=40, xalign=0.5)

(It really should have an id parameter added.)

There are three groups of UI functions, corresponding to the number of children they take.

The following UI functions do not take any children.

- ui.add
- ui.bar
- ui.imagebutton
- ui.input
- ui.key
- ui.label
- ui.null
- ui.text
- ui.textbutton
- ui.timer
- ui.vbar
- ui.hotspot
- ui.hotbar
- ui.spritemanager

The following UI functions take a single child. They must be given that child – use `ui.null()` if the child is missing.

- ui.button
- ui.frame
- ui.transform
- ui.window
- ui.drag

The following UI functions take multiple children. They continue taking children until `ui.close()` is called.

- ui.fixed
- ui.grid
- ui.hbox
- ui.side
- ui.vbox
- ui.imagemap
- ui.draggroup

There are a few UI functions that do not correspond to screen language statements, as they correspond to concepts that are not present in the screen language.

## Actions

Many of the displayables created in the screen language take actions as arguments. An action is one of three things:

- A callable Python object (like a function or bound method) that takes no arguments.
- An object of a class that inherits from the Action class.
- A list of other Actions.

The advantage to inheriting from the Action class is that it allows you to override the methods that determine when a button should be sensitive, and when it is selected.

class `Action`

  To define a new action, inherit from this class. Override the methods in this class to change the behavior of the action.

  `__call__`(self)

    This is the method that is called when the action is activated. In many cases, returning a non-None value from the action will cause the current interaction to end.

    This method must be overridden, as the default method will raise NotImplemented (and hence cause Ren’Py to report an error).

  `get_sensitive`(self)

    This is called to determine if the button with this action should be sensitive. It should return true if the button is sensitive.

    Note that __call__ can be called, even if this returns False.

    The default implementation returns True.

  `get_selected`(self)

    This should return true if the button should be rendered as a selected button, and false otherwise.

    The default implemention returns False.

  `get_tooltip`(self)

    This gets a default tooltip for this button, if a specific tooltip is not assigned. It should return the tooltip value, or None if a tooltip is not known.

    This defaults to returning None.

  `periodic`(self, st)

    This method is called once at the start of each interaction, and then is called periodically thereafter. If it returns a number, it will be called before that many seconds elapse, but it might be called sooner.

    The main use of this is to call `renpy.restart_interaction()` if the value of get_selected or get_sensitive should change.

    It takes one argument:

    st
      The number of seconds since the screen or displayable this action is associated with was first shown.
  `unhovered`(self)

    When the action is used as the hovered parameter to a button (or similar object), this method is called when the object loses focus.

To run an action from Python, use `renpy.run()`.

## BarValues

When creating a bar, vbar, or hotbar, a BarValue object can be supplied as the value property. Methods on the BarValue object are called to get the adjustment and styles.

class `BarValue`

  To define a new BarValue, inherit from this class and override some of the methods.

  `get_adjustment`(self)

    This method is called to get an adjustment object for the bar. It should create the adjustment with `ui.adjustment()`, and then return the object created this way.

    This method must be overridden, as the default method will raise NotImplemented (and hence cause Ren’Py to report an error).

  `get_style`(self)

    This is used to determine the style of bars that use this value. It should return a tuple of two style names or style objects. The first is used for a bar, and the second for vbar.

    This defaults to (“bar”, “vbar”).

  `get_tooltip`(self)

    This gets a default tooltip for this button, if a specific tooltip is not assigned. It should return the tooltip value, or None if a tooltip is not known.

    This defaults to returning None.

  `replaces`(self, other)

    This is called when a BarValue replaces another BarValue, such as when a screen is updated. It can be used to update this BarValue from the other. It is called before get_adjustment.

    Note that other is not necessarily the same type as self.

  `periodic`(self, st)

    This method is called once at the start of each interaction. If it returns a number of seconds, it will be called before that many seconds elapse, but it might be called sooner. It is called after get_adjustment.

    It can be used to update the value of the bar over time, like `AnimatedValue()` does. To do this, get_adjustment should store the adjustment, and periodic should call the adjustment’s changed method.

## InputValue

When creating an input, an InputValue object can be supplied as the value property. Methods on the InputValue object are called to get and set the text, determine if the input is editable, and handle the enter key being pressed.

class `InputValue`

  To define a new InputValue, inherit from this class, override some or all of the methods, and set the value of the default field.

  `default`

    If true, the input is eligible to be editable by default. (That is, it may be given the caret when the screen is shown.)

  `get_text`(self)

    Returns the default text of the input. This must be implemented.

  `set_text`(self, s)

    Called when the text of the input is changed, with the new text. This must be implemented.

  `enter`(self)

    Called when the user presses enter. If this returns a non-None value, that value is returned from the interacton. This may also raise renpy.IgnoreEvent() to ignore the press. Otherwise, the enter-press is propagated to other displayables.

  The following actions are available as methods on InputValue:

  `Enable`()

    Returns an action that enables text editing on the input.

  `Disable`()

    Returns an action that disables text editing on the input.

  `Toggle`()

    Returns an action that toggles text editing on the input.

## Creator-Defined Screen Language Statements

Ren’Py supports defining custom screen language statements. Creator-defined screen language statements are wrappers for the screen language use statement. Positional arguments remain positional arguments, properties become keyword arguments, and if the statement takes a block, so does the use statement. For example, the custom screen language statement:

    titledwindow "Test Window":
        icon "icon.png"

        text "This is a test."

becomes:

    use titledwindow("Test Window", icon="icon.png"):
        text "This is a test."

Creator-defined screen language statements must be registered in a `python early` block. What’s more, the filename containing the creator-defined statement must be be loaded earlier than any file that uses it. Since Ren’Py loads files in Unicode sort order, it generally makes sense to prefix the name of any file registering a user-defined statement with 01, or some other small number.

Creator-defined screen language statements are registered with the renpy.register_sl_statement function:

As an example of a creator-defined screen language statement, here’s an implementation of the `titledwindow` statement given above. First, the statement must be registered in a `python early` block in a file that is loaded early – a name like 01custom.rpy will often load soon enough. The registration call looks like:

    python early:
        renpy.register_sl_statement("titledwindow", positional=1, children=1).add_property("icon").add_property("pos")

Then, we define a screen that implements the custom statement. This screen can be defined in any file. One such screen is:

    screen titledwindow(title, icon=None, pos=(0, 0)):
        drag:
            pos pos

            frame:
                background "#00000080"

                has vbox

                hbox:
                    if icon is not None:
                        add icon

                    text title

                null height 15

                transclude