Roku SDK Documentation : Developing SceneGraph Applications

Table of Contents

Channel packages should include all the XML components they define in a top level directory named components (the top level directory in the channel application package contains the manifest file, the source directory, and so forth). When the channel is launched all the files with extension .xml in the components directory are loaded and added to the available types of nodes that can be created.

Currently, channel packages must include all of the XML component XML files that they use. In the future, we may provide a library of useful XML components for developers as well.

Set Up the Application Directory

Create an application directory with the following minimum subdirectories and files:

  • manifest file
  • source directory
  • components directory
  • images directory

Name this directory for the application it will contain, such as VideoStore. In most cases you will probably just copy an existing application directory (such as provided for the SceneGraph XML Tutorial), and modify, add, and rename files and directories for your new application, as described below.

Create or Modify a manifest File

The manifest file contains the following fields:




Many of the fields of the manifest file are optional or not required for the application to run. The title and subtitle fields can be useful for debugging, as are the _version fields. These can be set to aid debugging various versions of your application, but are not required.

The various _graphic_file_URI field values are used to specify a graphic that allows a user to select your application, and a "splash" screen that appears briefly before the application begins to run, often used while it is still loading.

The four application selection graphic files consist of two files each for both HD and SD user displays, "focus" and "side". These two files are specified in a SceneGraph manifest file only for backwards compatibility with past application selection user interfaces. The current SceneGraph application selection user interface only uses the focus graphic file.

The two application splash screen graphic files are for SD and HD user displays. Splash screens are not required but are recommended for your application. The color_specifier field value sets a default or opening display screen color before the splash screen loads, or if splash screen graphic files are not specified. The splash_min_time field sets the time in milliseconds that the splash screen should be displayed regardless of the load status of the application.

The graphics files specified in the manifest file should be included in the application package images directory, so the URI to set the path to the files should use pkg: resource prefix, such as pkg:/images/splash_sd.jpg. More information about the requirements and recommendations for the graphics files included in the application package can be found in Set Up the images Directory.

The following is an example of a manifest file.

manifest File Example
title=Test Application 
subtitle=A SceneGraph Test 



Set Up the source Directory

The source directory contains BrightScript code for the main applications execution thread, with the extension .brs. Since applications including SceneGraph scenes allow BrightScript code to either be embedded in, or used by, an XML component file in a <script> element, for many SceneGraph applications this directory will only contain a main.brs file to start the application. The main.brs file only need have enough BrightScript code to start the application by creating and displaying the scene specified in the SceneGraph scene.

The following shows a main.brs file that starts the application by creating and showing the scene defined in the SceneGraph scene named rectangleScene (the rectangleScene scene is defined in an XML component file in the components directory as described in Set Up the components Directory).

Example main.brs File
sub Main()
end sub
sub showChannelSGScreen()
  print "in showChannelSGScreen"
  screen = CreateObject("roSGScreen")
  m.port = CreateObject("roMessagePort")
  scene = screen.CreateScene("rectangleScene")
    msg = wait(0, m.port)
    msgType = type(msg)
    if msgType = "roSGScreenEvent"
    if msg.isScreenClosed() then return
    end if
  end while
end sub

 You can use this example main.brs file for your SceneGraph applications simply by adding the name of a Screen Graph scene defined in an XML component file, such as posterScene, as follows:

scene = screen.CreateScene("my_scene")

For example:

scene = screen.CreateScene("posterScene")

Similarly, you can control the flow of scenes through your application by creating and showing scenes as needed:

screen = CreateObject("roSGScreen")
m.port = CreateObject("roMessagePort")
scene = screen.CreateScene("another_scene")

Set Up the components Directory

The components directory contains all the XML component and associated BrightScript code files needed for your SceneGraph scene. The XML files must have the extension .xml, and as usual, BrightScript code files must have the extension .brs

Each XML component file contains a single <component> element that contains a specific SceneGraph node/element tree defining that component.

For example:

Example Scene Graph XML Component File
<?xml version="1.0" encoding="utf-8" ?>
<component name="rectangleScene" extends="Scene" >
<script type="text/brightscript" > 

sub init()
end sub 

In the above example, the SceneGraph component is a definition of a Scene node class named rectangleScene. The component definition consists of a <script> element, which defines some BrightScript code to be used to initialize rectangleScene, and a Rectangle node definition, that defines the location, size, and color of a rectangle to be shown on the display screen, with a node ID of bottomRectangle.

Complete information on creating XML component files and associated BrightScript code for your SceneGraph application can be found in:

Set Up the images Directory

Any graphic image files to be included in the application package itself should be copied into the images directory. As a minimum, the images directory must contain the application selection and splash screen graphic files described in Create or Modify a manifest File above. Other graphic files used in the application that will not be downloaded from your server should also be copied into the images directory.