Render Actions


Render Actions is a special type of stimulus that enables dynamic parameter changes to (i.e. animation of) other stimulus types.

Like other stimuli, a Render Actions stimulus must be added to the display queue with Queue Stimulus and made active with Update Stimulus Display. However, instead of drawing to the display like a normal stimulus, a Render Actions instance executes a set of attached actions. By changing the values of variables used in the parameters of other stimuli, these actions can alter the appearance of said stimuli on a frame-by-frame basis.

For example, consider the following circle stimulus, whose x_position and x_size parameters are given by variables:

var position = 0
var size = 0

circle ball (
    color = 1,0,0
    x_position = position
    x_size = size

By using a Render Actions instance to alter the variables’ values, we can turn this normally static circle into an animated one:

var elapsed_time = 0

render_actions update_position_and_size (
    elapsed_time = elapsed_time
    ) {
    // Vary position and size sinusoidally with a period of
    // three seconds
    position = -15 * cos(2*pi() * elapsed_time / 3s)
    size = 3 * (sin(2*pi() * elapsed_time / 3s) + 1) + 2

Inside our protocol, we can start the animation by queuing both stimuli and updating the stimulus display:

queue_stimulus (update_position_and_size)
live_queue_stimulus (ball)
update_display ()

(Note: In order for changes to its position and size to take effect immediately, we must live queue the circle.)

As with other dynamic stimuli, an experiment can pause, resume, stop, and restart a Render Actions stimulus. While the stimulus is paused, its attached actions do not execute, and the value reported by elapsed_time does not increase. Stopping and restarting the stimulus resets the elapsed time to zero.


Because a Render Actions stimulus executes on the stimulus display update thread, there are some restrictions on the actions that it can perform.

The following actions must not be executed by a Render Actions stimulus (either directly or via variable-attached actions), as they can cause the MWorks server to deadlock:

A Render Actions stimulus can safely use the following actions on other stimuli but not on itself. However, the effects of these actions may not be visible until the next display update pass:



Optional Parameters


Name of a variable in which to store the elapsed time (in microseconds) since the stimulus started playing (either implicitly due to autoplay being YES or via an explicit Play Dynamic Stimulus action).

If the stimulus has been paused (e.g. via Pause Dynamic Stimulus or Pause Experiment), the time elapsed while paused is excluded from the reported elapsed time.




If YES, the stimulus will begin executing its actions automatically (as if by an implicit Play Dynamic Stimulus action) after it has been queued and Update Stimulus Display has been invoked. It will also stop executing automatically (as if by an implicit Stop Dynamic Stimulus action) after it has been dequeued and Update Stimulus Display is invoked.




Controls when the stimulus is loaded. If no, the stimulus is loaded at experiment load time. If yes, the stimulus is loaded the first time it is queued. If explicit, the stimulus must be loaded explictly with Load Stimulus.


Name of the display on which the stimulus will be presented. If omitted, the default display (if available) will be used.


Allowed at top level:


Allowed parent:

Folder, Frame List Stimulus, Layer Stimulus, List Replicator, Movie Stimulus, Range Replicator, Stimulus Group

Allowed children: