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Using Expressions

Expressions unlock the power of NodeBox. Every parameter in NodeBox can use expressions. This allows you to:

  • Refer to other parameters on your own node or on other nodes
  • Use basic math to create interesting effects
  • Use animation by linking the parameter to the current frame.

The expression language is powerful and has support for arithmetic, functions and lists.

Toggling Expressions

To use expressions, you need to toggle it for that parameter.

Toggle Expression

  • Create a Rect node.
  • For the Height parameter, go to the down-arrow menu to the right and select “Toggle Expression”.
  • The height field now turns into a text field with a yellow background. This means we’re using expressions.
  • Type “width” (without the quotes) and hit enter.
  • Try changing the width parameter. Note that the height also moves, resulting in a square.
  • Try dragging the edges of the rectangle. Note that you can only move it in a square-like fashion.

Expressions can refer to other parameters using their short name. Often, this is the name of the parameter in lowercase, but not always. To see the short name, hover over the parameter name:

Viewing The Internal Name Hover over the parameter name to see the short name.

Names are always case-sensitive: differences in upper- and lowercase matter.

Referring To Other Nodes

Often it makes sense two have two objects relate to each other.

To relate one parameter to another, between nodes, use the syntax:


For example: rect1.width

  • Create an Ellipse node. Set Y to -75.00.
  • Create a Rect node. Set Y to 100.00 and Height to 150.00.
  • We want the rectangle to move together with the ellipse. In rect1 set X to the expression
  • In elipse1, drag the X parameter. Note that the rectangle follows along.

The node name is the name you see below the node. You can rename nodes by double-clicking the name or right-clicking the node and choosing “Rename”. Note that existing expressions will not be changed.

When copy-pasting nodes, expressions are not updated to new, internal names.

Arithmetic Operations

You can use basic arithmetic, such as adding, subtracting, dividing etc.

Here’s an example:

  • Create a Rect node.
  • Set Height to the expression
    width * 2
  • Every time you move the width, the height becomes double as large.

Expressions Arithmetic The height of the rectangle is always double the width.

There are many built-in operators in the NodeBox expression language. Here is a quick reference:

  • Add two numbers together. 5 + 3 ==> 8
  • Subtract two numbers. 12 - 4 ==> 8
  • Divide two numbers. 16 / 2 ==> 8
  • Raise a number to a power. 2 ** 3 ==> 8
  • Calculates the remainder of a division. 18 % 10 ==> 8

The expression reference has a more detailed explanation of all mathematical operations.

Using Functions

The NodeBox expression language uses functions for all but the simplest expressions, so it’s good to know what they are.

A function calculates something for you. You call the function with a number of arguments, and it gives you a value back. You can use this value directly, or pass it to another function.

To call a function, write this:

color(0.3, 0.5, 0.1, 0.95)

This structure is always the same:

  • The first part is the function name. NodeBox has a number of built-in functions, which you can find below.
  • After the name come the opening bracket: one at the beginning, one at the end. Even a function with no arguments still uses brackets., i.e. wave()
  • Then come the arguments. Each function has a required number of arguments. If you provide too little or too much, NodeBox will complain. You list the arguments in order and separate them using commas.
  • Finally, don’t forget the closing bracket!

Here are some other examples of functions:

  • Create a new color with a hue of 50%, a saturation of 30% and a brightness of 10%. Color values go from 0 to 1:
    hsb(0.5, 0.3, 0.1)
  • Generate a random number between 1 and 100, different for each copy:
    random(CNUM, 1, 100)
  • Copy stamp a value:
    stamp(“mysize”, 100)

Combining Functions

Soon, you will want to combine multiple functions. Let’s say that we want to have a hsb color with a different hue for each copy. For this, we need to combine functions.

Combining functions is not special. You need to apply the same logic as before, but instead you use a function as an argument. Here’s the example:

hsb(random("CNUM",0.0,1.0), 0.5, 0.8)

Instead of providing a normal value for the first argument of the hsb function, we provide another function, random, which return a random value for eacht copy between 0.5 and 0.8.

Here’s what NodeBox does to evaluate this:

  1. Call the random function. Let’s say this returns the value 0.77.
  2. Replace the random function with the output of the function. The function now looks like this: hsb(0.77, 0.5, 0.8)
  3. Call the hsb function and return a color object.

To summarize, NodeBox calculates the inner functions first and replace the results with the value.

Other Math

A lot of extra math functions are under the “math” package. You can refer to them by prepending “math.”: Those are functions, so use brackets. You can find the complete list of other math functions at the expression reference page.

Some examples: math.sin The arc sine of an angle. math.sin(0.5) math.cos The arc cosine of an angle. math.cos(0.3)

Working with Text

Pieces of text are called strings. Strings can be used in parameters that expect text, for example the textpath.text parameter.

A string is separated by quotes, like so:


This is to differentiate it from a keyword, which doesn’t use quotes.

Just as numbers, you can also add strings together:

“Hello” + “ “ + “there!”

You always need the quotes, also in functions:

stamp(“myvalue”, 42)

Working with Lists

You can create a list by using square brackets ([]).

A list looks like this:

[11, 22, 33, 44]

A list is only useful if you do something with it. For example, you can take a specific element out of it:

[11, 22, 33, 44][2]
==> 33

This returns the third element in the list. NodeBox indices start from zero.

Strings can also be a list. In this case, each letter of the list is a separate element. You can fetch the nth letter of the word using the following syntax:

==> "h"

A list can be a group of words.

["word", "sentence", "letter", "paragraph", "book"][3]
==> "paragraph"

A list can be a group of any type:

["Verdana", "Zapfino", "Georgia"][1]
==> "Zapfino"
[hsb(.5,.2,.1), hsb(.9,.6,.8)][1]
==> hsb(.9,.6,.8) // a pink-like color

You can call an item in the list by using a number as shown above or over the stamp function.

Here’s an example that uses copy stamping:

["word", "sentence", "letter", "paragraph", "book"][stamp("num", 0)]

Built-in Variables

NodeBox has a number of built-in variables you can use in expressions. These are all written in UPPERCASE to distinguish them from parameter names. They are:

  • FRAME: The current frame. See using animation for more explanation.
  • WIDTH: Width of the document, as defined in the document properties.
  • HEIGHT: Height of the document, as defined in the document properties.

Errors in Expressions

It happens. You make a mistake in an expression and the node turns red. How can we fix this error?

NodeBox reports expression errors in the source pane. But due to a bug, the pane does not update automatically. In the network pane you have to click away from the node (by clicking on the background), then click again on the node with the error.

Let’s show this in action by referring to a parameter that does not exist:

  • Create a Rect node.
  • Set Height to the expression (notice the typo)
  • The node turns red indicating there’s an error.
  • Click away from the node, on the network pane background. This deselects the node.
  • Now click the node again. You should see the following error in the source pane:

Expressions Error

The errors are often cryptic. Here, NodeBox is complaining about not being able to access “wit”, which should provide some clue that the parameter name is wrong.

More Information

Some of the expressions have a separate page. More information on copy stamping, data stamping and animation is on these pages:

  • Read the copy stamping page for general information on copy stamping.
  • Read the animation page for general information on animation.
  • Read the expression reference for detailed information on all built-in expressions.
  • The NodeBox expression engine is built using MVEL, an open-source expression language. Everything MVEL supports, NodeBox supports. Check out the MVEL Language Guide for more information.