Scripting

Gaia Sky offers the possibility to run Python scripts in the same JVM using Jython.

You can find some example scripts in the scripts folder of the project.

Hint

Add your own scripts to the folder $HOME/.gaiasky/scripts so that Gaia Sky can run them.

An interface is provided in order to encapsulate some complex-behaviour functions and to make scripting easier. This scripting interface is described in the following section.

The scripting API

The scripting API is a set of methods which can be called to interact with Gaia Sky. The available methods differ depending on the version of Gaia Sky.

API documentation

The only up-to-date API documentation for each version is in the interface header files themselves. Below is a list of links to the different APIs.

Using the scripting API

In order to import the scripting interface package in your script, you just need to import the default implementation EventScriptingInterface from the package gaia.cu9.ari.gaiaorbit.script:

# Import scripting interface
from gaia.cu9.ari.gaiaorbit.script import EventScriptingInterface

Then, we need to get the scripting interface instance before start using it.

gs = EventScriptingInterface.instance()

Now, we can start executing functions.

# Disable input
gs.disableInput()
gs.cameraStop()
gs.minimizeInterfaceWindow()

# Welcome
gs.setHeadlineMessage("Welcome to the Gaia Sky")
gs.setSubheadMessage("Explore Gaia, the Solar System and the whole Galaxy!")
[...]

Synchronizing with the main loop

Sometimes, when updating animations or creating camera paths, it is necessary to sync the execution of scripts with the thread which runs the main loop (main thread). However, the scripting engine runs scripts in separate threads asynchronously, making it a non-obvious task to achieve this synchronization. In order to fix this, a new mechanism has been added in Gaia Sky 2.0.3. Now, runnables can be parked so that they run at the end of the update-render processing of each loop cycle. A runnable is a class which extends java.lang.Runnable, and implements a very simple public void run() method.

Runnables can be posted, meaning that they are run only once at the end fo the current cycle, or parked, meaning that they run until they stop or they are unparked. Parked runnables must provide a name identifier in order to be later accessed and unparked.

Let’s see an example:

from gaia.cu9.ari.gaiaorbit.script import EventScriptingInterface
from java.lang import Runnable

class PrintRunnable(Runnable):
    def run(self):
        print("I RUN!")

class FrameCounterRunnable(Runnable):
    def __init__(self):
        self.n = 0

    def run(self):
        self.n = self.n + 1
        if self.n % 30 == 0:
            print "Number of frames: %d" % self.n


gs = EventScriptingInterface.instance()
# We post a simple runnable which prints "I RUN!" once
gs.postRunnable(PrintRunnable())
# We park a runnable which counts the frames and prints the current number
# of frames every 30 of them
gs.parkRunnable("frame_counter", FrameCounterRunnable())
gs.sleep(30.0)
# We unpark the frame counter
gs.unparkRunnable("frame_counter")
print "Exiting script"

In this example, we create two runnables. The first, which only prints ‘I RUN!” on the console, is posted using postRunnable(Runnable), so it only runs once. The second, which counts frames, is parked with parkRunnable(String, Runnable), so it runs until we unpark it with unparkRunnable(String). The parked runnable is run every cycle, so it is able to count the frames and print its progress every 30th execution.

A more useful example can be found here. In this script, a polyline is created between the Earth and the Moon. Then, a parked runnable is used to update the line points with the new postions of the bodies. Finally, time is started so that the bodies start moving and the line positions are updated correctly and in synch with the main thread.

More examples

You can find more examples by looking at the scripts folder in the Gaia Sky package.

How to run scripts

Each script is executed in its own thread in the virtual machine, and runs alongside Gaia Sky. In order to run a script, follow the procedure described in the Running scripts section.