.. _atl:

=====================================
Animation and Transformation Language
=====================================

The Animation and Transformation Language (ATL) provides a high-level way of
choosing a displayable to show, positioning it on the screen, and applying
transformations such as rotation, zoom, and alpha-modification. These can be
changed over time, and in response to events.

The Python equivalent of an ATL transform is the :func:`Transform`
displayable. There is no way to create an ATL transform programmatically.

Ren'Py Script Statements
========================

ATL can be included as part of three Ren'Py script statements.

.. _transform-statement:

Transform Statement
-------------------

The ``transform`` statement creates a transform that can be supplied as part of an
at clause. The syntax of the transform statement is:

.. productionlist:: script
    atl_transform : "transform" `name` "(" `parameters` ")" ":"
                  :    `atl_block`

The transform statement  must be run at init time. If it is found outside an
``init`` block, then it is automatically placed inside an ``init`` block with a
priority of 0. The transform may have a list of parameters, which must be
supplied when it is called.

`Name` must be a Python identifier. The transform created by the ATL block is
bound to this name.::

   transform left_to_right:
       xalign 0.0
       linear 2.0 yalign 1.0
       repeat

.. _atl-image-statement:

Image Statement With ATL Block
------------------------------

The second way to use ATL is as part of an ``image`` statement with ATL block.
This binds an image name to the given transform. As there's no way to supply
parameters to this transform, it's only useful if the transform defines an
animation. The syntax for an image statement with ATL block is:

.. productionlist:: script
    atl_image : "image" `image_name` ":"
              :    `atl_block`

::

    image eileen animated:
        "eileen_happy.png"
        pause 1.0
        "eileen_vhappy.png"
        pause 1.0
        repeat


Scene and Show Statements with ATL Block
----------------------------------------

The final way to use ATL is as part of a ``scene`` or ``show`` statement. This wraps
the image being shown inside an ATL transformation.

.. productionlist:: script
    atl_scene : `stmt_scene` ":"
              :     `atl_block`
    atl_show  : `stmt_show` ":"
              :     `atl_block`


::

    scene bg washington:
        zoom 2.0

    show eileen happy:
        xalign 1.0


ATL Syntax and Semantics
========================

An ATL block consists of one or more logical lines, all at the same
indentation, and indented relative to the statement containing the block.
Each logical line in an ATL block must contain one or more ATL statements.

There are two kinds of ATL statements: simple and complex. Simple statements
do not take an ATL block. A single logical line may contain one or more ATL
statements, separated by commas. A complex statement contains a block, must
be on its own line. The first line of a complex statement always ends with a
colon ``:``.

By default, statements in a block are executed in the order in which they
appear, starting with the first statement in the block. Execution terminates
when the end of the block is reached. Time statements change this, as
described in the appropriate section below.

Execution of a block terminates when all statements in the block have
terminated.

If an ATL statement requires evaluation of an expression, such evaluation
occurs when the transform is first added to the scene list. (Such as when
using a ``show`` statement or ``ui`` function.)

ATL Statements
==============

The following are the ATL statements.

Interpolation Statement
-----------------------

The interpolation statement is the main way that ATL controls transformations.

.. productionlist:: atl
    atl_interp : ( `warper` `simple_expression` | "warp" `simple_expression` `simple_expression` )?
               : ( `property` `simple_expression` ( "knot" `simple_expression` )*
               : | "clockwise"
               : | "counterclockwise"
               : | "circles" simple_expression
               : | simple_expression )*

The first part of the interpolation statement is used to select a function
that time-warps the interpolation. (That is, a function from linear time to
non-linear time.) This can either be done by giving the name of a warper
registered with ATL, or by giving the keyword "warp" followed by an
expression giving a function. Either case is followed by a number, giving the
number of seconds the interpolation should take.

If no warp function is given, the interpolation is instantaneous. Otherwise,
it persists for the amount of time given, and at least one frame.

The warper and duration are used to compute a completion fraction. This is
done by dividing the time taken by the interpolation by the duration of the
interpolation. This is clamped to the duration, and then passed to the
warper. The result returned by the warper is the completion fraction.

The interpolation statement can then contain a number of other clauses. When a
property and value are present, then the value is the value the property will
obtain at the end of the statement. The value can be obtained in several ways:

* If the value is followed by one or two knots, then spline motion is used.
  The starting point is the value of the property at the start of the
  interpolation, the end point is the property value, and the knots are used
  to control the spline.

* If the interpolation statement contains a "clockwise" or
  "counterclockwise" clause, circular motion is used, as described below.

* Otherwise, the value is linearly interpolated between the start and end
  locations, using the completion fraction.

If a simple expression is present, it should evaluate to a transform with only
a single interpolation statement, without a warper, splines, or circular
motion. The properties from the transform are processed as if they were
included in this statement.

Some sample interpolations are::

    show logo base:
         # Show the logo at the upper right side of the screen.
         xalign 1.0 yalign 0.0

         # Take 1.0 seconds to move things back to the left.
         linear 1.0 xalign 0.0

         # Take 1.0 seconds to move things to the location specified in the
         # truecenter transform. Use the ease warper to do this.
         ease 1.0 truecenter

         # Just pause for a second.
         pause 1.0

         # Set the location to circle around.
         alignaround (.5, .5)

         # Use circular motion to bring us to spiral out to the top of
         # the screen. Take 2 seconds to do so.
         linear 2.0 yalign 0.0 clockwise circles 3

         # Use a spline motion to move us around the screen.
         linear 2.0 align (0.5, 1.0) knot (0.0, .33) knot (1.0, .66)

An important special case is that the pause warper, followed by a time and
nothing else, causes ATL execution to pause for that amount of time.

Some properties can have values of multiple types. For example, the :propref:`xpos`
property can be an int, float, or absolute. The behavior is undefined when an
interpolation has old and new property values of different types.

Time Statement
--------------

The ``time`` statement is a simple control statement. It contains a single
`simple_expression`, which is evaluated to give a time, expressed as seconds
from the start of execution of the containing block.

.. productionlist:: atl
    atl_time : "time" `simple_expression`

When the time given in the statement is reached, the following statement
begins to execute. This transfer of control occurs even if a previous
statement is still executing, and causes any prior statement to immediately
terminate.

Time statements are implicitly preceded by a pause statement with an infinite
time. This means that if control would otherwise reach the time statement, it
waits until the time statement would take control.

When there are multiple time statements in a block, they must strictly
increase in order.

::

    image backgrounds:
        "bg band"
        time 2.0
        "bg whitehouse"
        time 4.0
        "bg washington"


Expression Statement
--------------------

An expression statement is a simple statement that starts with a simple
expression. It then contains an optional with clause, with a second simple
expression.

.. productionlist:: atl
    atl_expression :  `simple_expression` ("with" `simple_expression`)?

There are three things the first simple expression may evaluate to:

* If it's a transform, that transform is executed. With clauses are ignored
  when a transform is supplied.

* If it's an integer or floating point number,  it's taken as a number of
  seconds to pause execution for.

* Otherwise, the expression is interpreted to be a displayable. This
  displayable replaces the child of the transform when this clause executes,
  making it useful for animation. If a with clause is present, the second
  expression is evaluated as a transition, and the transition is applied to
  the old and new displayables.

::

    image atl example:
         # Display logo_base.png
         "logo_base.png"

         # Pause for 1.0 seconds.
         1.0

         # Show logo_bw.png, with a dissolve.
         "logo_bw.png" with Dissolve(0.5, alpha=True)

         # Run the move_right transform.
         move_right

Pass Statement
--------------

.. productionlist:: atl
    atl_pass : "pass"

The ``pass`` statement is a simple statement that causes nothing to happen. This
can be used when there's a desire to separate statements, like when there are
two sets of choice statements that would otherwise be back-to-back.

Repeat Statement
----------------


The ``repeat`` statement is a simple statement that causes the block containing it
to resume execution from the beginning. If the expression is present, then it
is evaluated to give an integer number of times the block will execute. (So a
block ending with ``repeat 2`` will execute at most twice.)

.. productionlist:: atl
    atl_repeat : "repeat" (`simple_expression`)?

The repeat statement must be the last statement in a block.::

    show logo base:
        xalign 0.0
        linear 1.0 xalign 1.0
        linear 1.0 xalign 0.0
        repeat


Block Statement
---------------

The ``block`` statement is a complex statement that contains a block of ATL statements.
This can be used to group statements that will repeat.

.. productionlist:: atl
    atl_block_stmt : "block" ":"
                   :      `atl_block`

::

    label logo base:
        alpha 0.0 xalign 0.0 yalign 0.0
        linear 1.0 alpha 1.0

        block:
            linear 1.0 xalign 1.0
            linear 1.0 xalign 0.0
            repeat

Choice Statement
----------------

The ``choice`` statement is a complex statement that defines one of a set of
potential choices. Ren'Py will pick one of the choices in the set, and
execute the ATL block associated with it, and then continue execution after
the last choice in the choice set.

.. productionlist:: atl
   atl_choice : "choice" (`simple_expression`)? ":"
              :     `atl_block`

Choice statements are greedily grouped into a choice set when more than one
choice statement appears consecutively in a block. If the `simple_expression`
is supplied, it is a floating-point weight given to that block, otherwise 1.0
is assumed.

::

    image eileen random:
        choice:
            "eileen happy"
        choice:
            "eileen vhappy"
        choice:
            "eileen concerned"

        pause 1.0
        repeat

Parallel Statement
------------------

The ``parallel`` statement is used to define a set of ATL blocks to execute in
parallel.

.. productionlist:: atl
    atl_parallel : "parallel" ":"
                 :    `atl_block`

Parallel statements are greedily grouped into a parallel set when more than
one parallel statement appears consecutively in a block. The blocks of all
parallel statements are then executed simultaneously. The parallel statement
terminates when the last block terminates.

The blocks within a set should be independent of each other, and manipulate
different properties. When two blocks change the same property, the result is
undefined.

::

    show logo base:
        parallel:
            xalign 0.0
            linear 1.3 xalign 1.0
            linear 1.3 xalign 0.0
            repeat
        parallel:
            yalign 0.0
            linear 1.6 yalign 1.0
            linear 1.6 yalign 0.0
            repeat

Event Statement
---------------

The ``event`` statement is a simple statement that causes an event with the given
name to be produced.

.. productionlist:: atl
    atl_event : "event" `name`

When an event is produced inside a block, the block is checked to see if an
event handler for the given name exists. If it does, control is transferred
to the event handler. Otherwise, the event propagates to any containing event
handler.

On Statement
------------

The ``on`` statement is a complex statement that defines an event handler. On
statements are greedily grouped into a single statement. On statement can
handle a single event name, or a comma-separated list of event names.

.. productionlist:: atl
   atl_on : "on" `name` [ "," `name` ] * ":"
          :      `atl_block`

The on statement is used to handle events. When an event is handled, handling
of any other event ends and handing of the new event immediately starts. When
an event handler ends without another event occurring, the ``default`` event
is produced (unless were already handing the ``default`` event).

Execution of the on statement will never naturally end. (But it can be ended
by the time statement, or an enclosing event handler.)

::

    show logo base:
        on show:
            alpha 0.0
            linear .5 alpha 1.0
        on hide:
            linear .5 alpha 0.0

    transform pulse_button:
        on hover, idle:
            linear .25 zoom 1.25
            linear .25 zoom 1.0

Contains Statement
------------------

The ``contains`` statement sets the displayable contained by this ATL transform
(the child of the transform). There are two variants of the contains
statement.

The contains expression variant takes an expression, and sets that expression
as the child of the transform. This is useful when an ATL transform wishes to
contain, rather than include, a second ATL transform.

.. productionlist:: atl
    atl_contains : "contains" `expression`

::

    transform an_animation:
        "1.png"
        pause 2
        "2.png"
        pause 2
        repeat

    image move_an_animation:
        contains an_animation

        # If we didn't use contains, we'd still be looping and
        # would never reach here.
        xalign 0.0
        linear 1.0 yalign 1.0


The contains block allows one to define an ATL block that is used for the
child of this ATL transform. One or more contains block statements will be
greedily grouped together, wrapped inside a :func:`Fixed`, and set as the
child of this transform.

.. productionlist:: atl
    atl_counts : "contains" ":"
         `atl_block`

Each block should define a displayable to use, or else an error will occur.
The contains statement executes instantaneously, without waiting for the
children to complete. This statement is mostly syntactic sugar, as it allows
arguments to be easily passed to the children.

::

    image test double:
        contains:
            "logo.png"
            xalign 0.0
            linear 1.0 xalign 1.0
            repeat

        contains:
            "logo.png"
            xalign 1.0
            linear 1.0 xalign 0.0
            repeat

Function Statement
------------------

The ``function`` statement allows ATL to use Python functions to control the ATL
properties.

.. productionlist:: atl
    atl_function : "function" `expression`

The functions have the same signature as those used with :func:`Transform`:

* The first argument is a transform object. Transform properties can be set
  on this object.

* The second argument is the shown timebase, the number of seconds since the
  function began executing.

* The third argument is the the animation timebase, which is the number of
  seconds something with the same tag has been on the screen.

* If the function returns a number, it will be called again after that
  number of seconds has elapsed. (0 seconds means to call the function as
  soon as possible.) If the function returns None, control will pass to the
  next ATL statement.

::

    init python:
        def slide_function(trans, st, at):
            if st > 1.0:
                trans.xalign = 1.0
                return None
            else:
                trans.xalign = st
                return 0

    label start:
        show logo base:
            function slide_function
            pause 1.0
            repeat


.. _warpers:

Warpers
=======

A warper is a function that can change the amount of time an interpolation
statement considers to have elapsed. The following warpers are defined by
default. They are defined as functions from t to t', where t and t' are
floating point numbers, with t ranging from 0.0 to 1.0 over the given
amount of time. (If the statement has 0 duration, then t is 1.0 when it runs.)
t' should start at 0.0 and end at 1.0, but can be greater or less.

``pause``
    Pause, then jump to the new value. If t == 1.0, t = 1.0. Otherwise, t'
    = 0.0.

``linear``
    Linear interpolation. t' = t

``ease``
    Start slow, speed up, then slow down. t' = .5 - math.cos(math.pi
    * t) / 2.0

``easein``
    Start fast, then slow down. t' = math.cos((1.0 - t) * math.pi / 2.0

``easeout``
    Start slow, then speed up. t' = 1.0 - math.cos(t * math.pi / 2.0)

In addition, most of Robert Penner's easing functions are supported. To
make the names match those above, the functions have been renamed
somewhat. Graphs of these standard functions can be found at
http://www.easings.net/.

.. include:: inc/easings

New warpers can be defined using the ``renpy.atl_warper`` decorator, in a ``python
early`` block. It should be placed in a file that is parsed before any file
that uses the warper. This looks like::

    python early hide:

        @renpy.atl_warper
        def linear(t):
            return t

.. _transform-properties:

List of Transform Properties
============================

The following transform properties exist.

When the type is given as position, it may be an int, ``renpy.absolute``, or
float. If it's a float, it's interpreted as a fraction of the size of the
containing area (for :propref:`pos`) or displayable (for :propref:`anchor`).

Note that not all properties are independent. For example, :propref:`xalign` and :propref:`xpos`
both update some of the same underlying data. In a parallel statement, only
one block should adjust horizontal position, and one should adjust vertical
positions. (These may be the same block.) The angle and radius properties set
both horizontal and vertical positions.

.. transform-property:: pos

    :type: (position, position)
    :default: (0, 0)

    The position, relative to the top-left corner of the containing
    area.

.. transform-property:: xpos

    :type: position
    :default: 0

    The horizontal position, relative to the left side of the
    containing area.

.. transform-property:: ypos

    :type: position
    :default: 0

    The vertical position, relative to the top of the containing area.

.. transform-property:: anchor

    :type: (position, position)
    :default: (0, 0)

    The anchor position, relative to the top-left corner of the
    displayable.

.. transform-property:: xanchor

    :type: position
    :default: 0

    The horizontal anchor position, relative to the left side of the
    displayable.

.. transform-property:: yanchor

    :type: position
    :default: 0

    The vertical anchor position, relative to the top of the
    displayable.

.. transform-property:: align

    :type: (float, float)
    :default: (0.0, 0.0)

    Equivalent to setting pos and anchor to the same value.

.. transform-property:: xalign

    :type: float
    :default: 0.0

    Equivalent to setting xpos and xanchor to this value.

.. transform-property:: yalign

    :type: float
    :default: 0.0

    Equivalent to setting ypos and yanchor to this value.

.. transform-property:: xoffset

    :type: float
    :default: 0.0

    The number of pixels the displayable is offset by in the horizontal
    direction. Positive values offset toward the right.

.. transform-property:: yoffset

    :type: float
    :default: 0.0

    The number of pixels the displayable is offset by in the vertical
    direction. Positive values offset toward the bottom.


.. transform-property:: xcenter

    :type: float
    :default: 0.0

    Equivalent to setting xpos to the value of this property, and
    xanchor to 0.5.

.. transform-property:: ycenter

    :type: float
    :default: 0.0

    Equivalent to setting ypos to the value of this property, and
    yanchor to 0.5.

.. transform-property:: rotate

    :type: float or None
    :default: None

    If None, no rotation occurs. Otherwise, the image will be rotated
    by this many degrees clockwise. Rotating the displayable causes it
    to be resized, according to the setting of rotate_pad, below. This
    can cause positioning to change if xanchor and yanchor are not
    0.5.

.. transform-property:: rotate_pad

    :type: boolean
    :default: True

    If True, then a rotated displayable is padded such that the width
    and height are equal to the hypotenuse of the original width and
    height. This ensures that the transform will not change size as
    its contents rotate. If False, the transform will be given the
    minimal size that contains the transformed displayable. This is
    more suited to fixed rotations.

.. transform-property:: transform_anchor

   :type: boolean
   :default: False

   If true, the anchor point is located on the cropped child, and is scaled
   and rotated as the child is transformed. Effectively, this makes the
   anchor the point that the child is rotated and scaled around.

.. transform-property:: zoom

    :type: float
    :default: 1.0

    This causes the displayable to be zoomed by the supplied
    factor.

.. transform-property:: xzoom

    :type: float
    :default: 1.0

    This causes the displayable to be horizontally zoomed by the
    supplied factor. A negative value causes the image to be
    flipped horizontally.

.. transform-property:: yzoom

   :type: float
   :default: 1.0

   This causes the displayable to be vertically zoomed by the supplied
   factor. A negative value causes the image to be flipped vertically.

.. transform-property:: nearest

    :type: boolean
    :default: None

    If True, the displayable and its children are drawn using nearest-neighbor
    filtering. If False, the displayable and its children are drawn using
    bilinear filtering. If None, this is inherited from the parent, or
    :var:`config.nearest_neighbor`, which defaults to False.

.. transform-property:: alpha

    :type: float
    :default: 1.0

    This controls the opacity of the displayable.

    The alpha transform is applied to each image comprising the child of
    the transform independently. This can lead to unexpected results when
    the children overlap, such as as seeing a character through clothing.
    The :func:`Flatten` displayable can help with these problems.

.. transform-property:: additive

    :type: float
    :default: 0.0

    This controls how much additive blending Ren'Py performs. When 1.0,
    Ren'Py draws using the ADD operator. When 0.0, Ren'Py draws using
    the OVER operator.

    Additive blending is performed on each child of the transform independently.

    Fully additive blending doesn't alter the alpha channel of the destination,
    and additive images may not be visible if they're not drawn directly onto
    an opaque surface. (Complex operations, like viewport, :func:`Flatten`, :func:`Frame`,
    and certain transitions may cause problems with additive blending.)

    .. warning::

        Additive blending is only supported by hardware-based renderers, such
        as the OpenGL and DirectX/ANGLE renderers. The software renderer will
        draw additive images incorrectly.

        Once the graphics system has started, ``renpy.get_renderer_info()["additive"]``
        will be true if additive blending is supported.


.. transform-property:: around

    :type: (position, position)
    :default: (0.0, 0.0)

    If not None, specifies the polar coordinate center, relative to
    the upper-left of the containing area. Setting the center using
    this allows for circular motion in position mode.

.. transform-property:: alignaround

    :type: (float, float)
    :default: (0.0, 0.0)

    If not None, specifies the polar coordinate center, relative to
    the upper-left of the containing area. Setting the center using
    this allows for circular motion in align mode.

.. transform-property:: angle

    :type: float

    Get the angle component of the polar coordinate position. This is
    undefined when the polar coordinate center is not set.

.. transform-property:: radius

    :type: position

    Get the radius component of the polar coordinate position. This is
    undefined when the polar coordinate center is not set.

.. transform-property:: crop

    :type: None or (int, int, int, int) or (float, float, float, float)
    :default: None

    If not None, causes the displayable to be cropped to the given
    box. The box is specified as a tuple of (x, y, width, height).
    If floats are given and ``crop_relative`` is true, the components are
    taken as a fraction of the width and hight of the source image.
    Otherwise, the components are considered to be an absolute number
    of pixels.

.. transform-property:: crop_relative

    :type: boolean
    :default: False

    If True, float components of crop are take as a fraction of the width
    and height of the source image.

.. transform-property:: corner1

    :type: None or (int, int)
    :default: None

    If not None, gives the upper-left corner of the crop box. This
    takes priority over crop.

.. transform-property:: corner2

    :type: None or (int, int)
    :default: None

    If not None, gives the lower right corner of the crop box. This
    takes priority over crop.

.. transform-property:: size

    :type: None or (int, int)
    :default: None

    If not None, causes the displayable to be scaled to the given
    size.

.. transform-property:: maxsize

    :type: None or (int, int)
    :default: None

    If not None, causes the displayable to be scaled so that it fits
    within a box of this size, while preserving aspect ratio. (Note that
    this means that one of the dimensions may be smaller than the size
    of this box.)

.. transform-property:: subpixel

    :type: boolean
    :default: False

    If True, causes things to be drawn on the screen using subpixel
    positioning.

.. transform-property:: delay

    :type: float
    :default: 0.0

    If this transform is being used as a transition, then this is the
    duration of the transition.

.. transform-property:: events

    :type: boolean
    :default: True

    If true, events are passed to the child of this transform. If false,
    events are blocked. (This can be used in ATL transforms to prevent
    events from reaching the old_widget.)

.. transform-property:: xpan

    :type: None or float
    :default: None

    If not None, this interpreted as an angle that is used to pan horizontally
    across a 360 degree panoramic image. The center of the image is used as the
    zero angle, while the left and right edges are -180 and 180 degrees,
    respectively.

.. transform-property:: ypan

    :type: None or float
    :default: None

    If not None, this interpreted as an angle that is used to pan vertically
    across a 360 degree panoramic image. The center of the image is used as the
    zero angle, while the top and bottom edges are -180 and 180 degrees,
    respectively.

.. transform-property:: xtile

    :type: int
    :default: 1

    The number of times to tile the image horizontally. (This is ignored when
    xpan is given.)

.. transform-property:: ytile

    :type: int
    :default: 1

    The number of times to tile the image vertically. (This is ignored when
    ypan is given.)

These properties are applied in the following order:

#. tile
#. crop, corner1, corner2
#. size, maxsize
#. zoom, xzoom, yzoom
#. pan
#. rotate
#. position properties


Circular Motion
===============

When an interpolation statement contains the ``clockwise`` or
``counterclockwise`` keywords, the interpolation will cause circular motion.
Ren'Py will compare the start and end locations and figure out the polar
coordinate center. Ren'Py will then compute the number of degrees it will
take to go from the start angle to the end angle, in the specified direction
of rotation. If the circles clause is given, Ren'Py will ensure that the
appropriate number of circles will be made.

Ren'Py will then interpolate the angle and radius properties, as appropriate,
to cause the circular motion to happen. If the transform is in align mode,
setting the angle and radius will set the align property. Otherwise, the pos
property will be set.

External Events
===============

The following events can be triggered automatically:

``start``
    A pseudo-event, triggered on entering an ``on`` statement, if no event of
    higher priority has happened.

``show``
    Triggered when the transform is shown using the show or scene
    statement, and no image with the given tag exists.

``replace``
    Triggered when transform is shown using the ``show`` statement, replacing
    an image with the given tag.

``hide``
    Triggered when the transform is hidden using the ``hide`` statement or its
    Python equivalent.

    Note that this isn't triggered when the transform is eliminated via
    the scene statement or exiting the context it exists in, such as when
    exiting the game menu.

``replaced``
    Triggered when the transform is replaced by another. The image will
    not actually hide until the ATL block finishes.

``update``
    Triggered when a screen is updated without being shown or replacing
    another screen. This happens in rare but possible cases, such as when
    the game is loaded and when styles or translations change.

``hover``, ``idle``, ``selected_hover``, ``selected_idle``
   Triggered when button containing this transform, or a button contained
   by this transform, enters the named state.

