Outline Layer


About Outline Layers

Outline Layers are used to hold strokes or edges of filled shapes. They give a cartoon look to an animation when added as the edge of the filled shapes. Also standalone Outlines (strokes) are used to define fold of 3D drawings and used together with shadows (created using gradients or feathering) are the basis of an artist’s work.

To create an Outline Layer use the Spline Tool and check Create Outline in the Tool Options Panel. Once you finish the definition of the geometry of your outline and after pressing the Make Spline button (or selecting another tool or state) you create the Outline Layer with the current Outline Color.

Depending on the options you choose in the Tool Options Panel other like Star Tool or Circle Tool can also create Outline Layers.

Using the Layer Menu Make Advanced Outline, Make Outline or Make Region commands you can also create those layers.

Parameters of Outline Layers

The parameters of the Outline layers are:

Name Value Type
Type_real_icon.png Z Depth 0.000000 real
Type_real_icon.png Amount 1.000000 real
Type_integer_icon.png Blend Method Composite integer
Type_color_icon.png Color p_color_green.png color
Type_vector_icon.png Origin 0.000000u,0.000000u vector
Type_bool_icon.png Invert p_checkbox_off.png bool
Type_bool_icon.png Antialiasing p_checkbox_off.png bool
Type_real_icon.png Feather 0.000000pt real
Type_integer_icon.png Type of Feather Fast Gaussian Blur integer
Type_integer_icon.png Winding Style Non Zero integer
Type_list_icon.png Vertices List list (Spline)
Type_real_icon.png Outline Width 2.000000pt real
Type_real_icon.png Expand 0.000000pt real
Type_bool_icon.png Sharp Cusps p_checkbox_off.png bool
Type_bool_icon.png Rounded Begin p_checkbox_off.png bool
Type_bool_icon.png Rounded End p_checkbox_off.png bool
Type_real_icon.png Loopyness 1.000000 real
Type_bool_icon.png Homogeneous p_checkbox_off.png bool

Specific parameters for Outline Layers

The first 11 parameters of the Outline are common parameters that are shared for several types of Layers. Click on the links to see their definitions. Only the particular parameters for the Outline Layer are described here.

This is a sample screenshot of an Outline Layer in action:


Outline width

The Outline width parameter is a float value in pixels that represents the basic value of the width for all the points of the curve at the same time. It works together with the width parameter of the vertices’ child values. So setting the Outline Width to 1.0px then the resulting value for the rendered width in that vertex comes from this formula: W = OLW * VW + 2E.


  • W = resulting width of the outline at that vertex.
  • OLW = overall parameter for the width of all the vertices (that is the Outline Width parameter).
  • VW = specific vertex width value.
  • E = value of the Expand parameter.

The width handle would show the radius value for that vertex (W/2).

The width that ends up being used for each vertex is ((VertexWidth * OutLineWidth) + Expand*2):

Starting image After doubling the value of Outline Width

It’s possible to specify negative values for the width values, which kind of turns the vertex inside out. Here’s an example where the left vertex has a negative width and the right has a positive width. Note how the edges of the spline between the vertices cross each other in the middle:



The Expand parameter is similar to the Outline Width parameter, but rather than being multiplied by each vertex’s width, it is added to the radius of each vertex. In other words (2*Expand) is added to the diameter of each vertex.

The width that ends up being used for each vertex is ((VertexWidth * OutLineWidth) + Expand*2):

Zero Expand Non-zero Expand

Sharp cups

Enabling Sharp Cusps makes the corners pointy when the tangents are split:

No Sharp Cusps With Sharp Cusps

Rounded Begin

Enabling Rounded Begin makes the start of the outline rounded:

no Rounded Begin Rounded Begin

Note: With cairo render activated, if the quality is superior to 6, enabling Rounded Begin enable also RRounded End.

Rounded End

Enabling Rounded End makes the end of the outline rounded:

No Rounded End With Rounded End

Note: With cairo render activated, if the quality is superior to 6, enabling Rounded End enable also Rounded Begin.


This parameter currently does absolutely nothing at all!


Enabling ‘Homogeneous’ changes the way that the width of the outline changes from one spline point to the next. Each point in the spline has its own width, and the spline has its own ‘Outline Width’ and ‘Expand’ parameters which are used to give the final width at each spline point. The ‘Homogeneous’ parameter controls how the width is interpolated between two neighboring spline points:

  • When ‘Homogeneous’ isn’t checked, the width is interpolated linearly with the spline’s ‘t’ parameter.
  • When ‘Homogeneous’ is checked, the width is interpolated linearly with the spline’s length.

Turning off homogeneous often makes the fat end of a spline look lumpy. Maybe that’s a bug:

not homogeneous homogeneous


The Antialiasing Parameter‎ isn’t specific to the Outline layer, but it is particularly useful for the Outline layer. It makes the edges appear smoother:

not antialiased antialiased

Note : File used