Helpers

Transform

Layer transform

Composition Diagram for Transform

Attribute	Type	Title	Description
`a`	Position	Anchor Point	Anchor point: a position (relative to its parent) around which transformations are applied (ie: center for rotation / scale)
`p`	Splittable Position	Position	Position / Translation
`r`	Scalar	Rotation	Rotation in degrees, clockwise
`s`	Vector	Scale	Scale factor, `[100, 100]` for no scaling
`o`	Scalar	Opacity	Opacity
`sk`	Scalar	Skew	Skew amount as an angle in degrees
`sa`	Scalar	Skew Axis	Direction along which skew is applied, in degrees (`0` skews along the X axis, `90` along the Y axis)

To make the anchor point properly line up with the center of location, p and a should have the same value.

This example allows you to tweak transform attributes and see how the shape changes.

The anchor point is highlighted with an orange dot.

Anchor X	256
Anchor Y	256
Position X	256
Position Y	256
Scale X	100
Scale Y	100
Rotation	0
Skew	0
Skew Angle	0
Opacity	100

Transforms the parent's coordinate system.

When calculating the final transform, properties MUST be applied as follows:

Translate by $- a$
Scale by $\frac{s}{100}$
If sk≠0:
1. Rotate by $- s a$
2. Skew x by $\tan (- s k)$
3. Rotate by $s a$
Rotate by $- r$
Translate by $p$

Steps that have no effect MAY be skipped.

Assuming a transform matrix with the following layout, with the labels equivalent to the CSS matrix transform:

(\begin{matrix} a & b & 0 \\ c & d & 0 \\ e & f & 1 \end{matrix})

The final transform is given by chaining transform matrices for each transform step:

\begin{matrix} (\begin{matrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ - a . x & - a . y & 1 \end{matrix}) \times (\begin{matrix} \frac{s . x}{100} & 0 & 0 \\ 0 & \frac{s . y}{100} & 0 \\ 0 & 0 & 1 \end{matrix}) \times \\ \times & (\begin{matrix} \cos (- s a) & \sin (- s a) & 0 \\ - \sin (- s a) & \cos (- s a) & 0 \\ 0 & 0 & 1 \end{matrix}) \times (\begin{matrix} 1 & \tan (- s k) & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{matrix}) \times (\begin{matrix} \cos (s a) & \sin (s a) & 0 \\ - \sin (s a) & \cos (s a) & 0 \\ 0 & 0 & 1 \end{matrix}) \times \\ \times & (\begin{matrix} \cos (- r) & \sin (- r) & 0 \\ - \sin (- r) & \cos (- r) & 0 \\ 0 & 0 & 1 \end{matrix}) \times (\begin{matrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ p . x & p . y & 1 \end{matrix}) \end{matrix}

Note that if the transform matrix is transposed compared to the above:

(\begin{matrix} a & c & e \\ b & d & f \\ 0 & 0 & 1 \end{matrix})

The operations need to be chained using right multiplication instead of left multiplication.

Visual Object

Composition Diagram for Visual Object

Attribute	Type	Title	Description
`nm`	`string`	Name	Human readable name, as seen from editors and the like

Marker

Defines named portions of the composition.

Attribute	Type	Title	Description
`cm`	`string`	Comment	Comment
`tm`	`number`	Time	Time
`dr`	`number`	Duration	Duration

Slots

Slots are a way to define a property value once and use the value in multiple properties. Slot definitions are in a dictionary, the slot definition key is the key that is used to match all properties with a sid field to the same key for replacement.

Slot

Defines a property value that will be set to all matched properties

Attribute	Type	Title	Description
`p`		Property Value	Property Value

Slotabble Object

Object that may have its value replaced with a slot value

Composition Diagram for Slottable Object

Attribute	Type	Title	Description
`sid`	`string`	Slot Id	Identifier to look up the slot

Slotabble Property

Property that may have its value replaced with a slot value

Composition Diagram for Slottable Property

Attribute	Type	Title	Description
`sid`	`string`	Slot Id	Identifier to look up the slot

Scale X	100
Scale Y	100
Rotation	0
Opacity	100

Mask

Mask for layer content.

Attribute	Type	Title	Description
`mode`	Mask Mode	Mode	Mode
`o`	Scalar	Opacity	Mask opacity, as a percentage [0..100].
`pt`	Bezier	Shape	Mask shape

Masks provide single-channel coverage information (alpha channel) that modulates the layer's content.

When multiple masks are specified, they are combined (blended) into a single coverage buffer, in order, based on the mode operator.

Masks are specified in terms of a Path plus additional properties. For a given mask path, the coverage $C_{p a t h}$ is $1$ inside the path, $0$ outside the path, and possibly in the $[0 . .1]$ range along the path edges (anti-aliasing).

The coverage for a given Mask is

C = {\begin{matrix} C_{p a t h} \cdot o p a c i t y, & when i n v = f a l s e \\ C_{p a t h}^{- 1} \cdot o p a c i t y, & when i n v = t r u e \end{matrix}

and the cumulative coverage for all masks is

C_{c u m u l a t i v e} = \prod_{k = 1}^{n} C_{k}

where the product operator is determined by mode. Then the final layer coverage (alpha channel) is

C_{l a y e r}' = C_{l a y e r} \cdot C_{c u m u l a t i v e}

Example

Opacity 

100

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