BrightScript Engine Current Limitations

The BrightScript Engine implements the BrightScript language specification up to Roku OS 15.0. However, some features and components remain unsupported or only partially implemented. These limitations fall into three categories: features planned for future development, components that will remain as mock objects for compatibility purposes, and functionality considered outside the project's scope. The following sections detail each category and its current status.

In Scope (to be developed/fixed in future releases)

• Roku SceneGraph SDK components are currently being implemented in this branch and released as pre-release alpha, so far we support:
  • Load XML component files and create SceneGraph nodes tree.
  • Basic support for roSGNode and roSGScreen components and rendering.
  • The Task node is implemented but its behavior is limited:
    • For now only 10 task threads are supported per application
    • The m.global object can have children, but changes on those nodes are not shared among the threads
    • Only one port instance can be used on Task init() to observe fields
  • The following nodes are already implemented:
    • The basic nodes: ContentNode, Group, Scene, Global, Font, Timer, Rectangle, Label, ScrollingLabel, Poster, LayoutGroup and RSGPalette
    • Grids and list nodes based on ArrayGrid: LabelList, CheckList, RadioButtonList, MarkupList, MarkupGrid, RowList and ZoomRowList
    • Dialog related nodes: Dialog, KeyboardDialog, StandardDialog, StandardProgressDialog, StdDlgProgressItem, StdDlgContentArea and StdDlgTitleArea
    • Media related nodes: Audio, SoundEffect, Video and TrickPlayBar
    • Other supported nodes: Button, ButtonGroup, BusySpinner, Overhang, Keyboard, MiniKeyboard, TextEditBox and ChannelStore
  • Some of the nodes listed above may not have full functionality yet, please open a GitHub issue if you find any problem or missing feature.
  • The support for animations is not yet implemented, including the focus change animation on grid and list nodes.
  • All other nodes are either mocked or not implemented yet, and if used will be created as a plain Node.
  • The component roRenderThreadQueue introduced in Roku OS 15 is still not implemented.
• The following components are also not implemented yet:
  • Text to Speech components: roAudioGuide, roMicrophone and roTextToSpeech
  • Signing Algorithm components: roDSA and roRSA
• Audio playback is implemented via roAudioResources, SoundEffect, roAudioPlayer and Audio node, but with some limitations:
  • Only one instance of roAudioPlayer or Audio node should be used, if more are created those will share the content playlist.
  • If the roAudioPlayer or Audio node instance is destroyed the audio keeps playing, make sure to stop the playback before discarding the object.
  • No Timed Metadata support.
• The component roAudioMetadata only supports MP3 (for now).
• The component roImageMetadata only supports JPEG images (for now).
• Video playback is implemented via roVideoPlayer and Video node, but with some limitations:
  • If the instance of roVideoPlayer or Video is destroyed the video keeps playing, make sure to stop before discarding the object.
  • The following roVideoPlayer methods are not supported, implemented as mock: setCGMS, setMaxVideoDecodeResolution, setTimedMetadataForKeys, getCaptionRenderer
  • Check what formats (container and codec) can be used on each browser, using roDeviceInfo.canDecodeVideo(), to make sure your video can be played.
  • Subtitles are only supported for HLS streams and only in Video node, the roVideoPlayer does not support subtitles for now.
  • BIF (Base Index Frames) thumbnails are not yet supported.
  • DASH streams are not yet supported.
• The component roUrlTransfer is implemented with basic functionality but with the following limitations:
  • To make a web app access urls from domains other than the one it is hosted, the Cross-Origin Resource Sharing (CORS) browser policy requires the server called to respond with the header Access-Control-Allow-Origin, read more.
    • A simple way to overcome this limitation is to use a CORS proxy like the cors-anywhere, see customization documentation to learn how to configure brs-engine to use it.
    • If you are using a Chromium based browser (Chrome, Edge, Brave, etc) you can install this extension to bypass CORS.
  • The async methods are actually synchronous and evaluated when WaitMessage or GetMessage are called.
  • Custom/Self-Signed SSL certificates are not supported, the engine will use default browser client certificate database.
  • As custom certificates are not supported these methods are just mocked and do nothing: EnablePeerVerification, EnableHostVerification, SetCertificatesDepth.
  • Cookies are only partially supported, if EnableCookies is called and EnableFreshConnection is set to false, then Cookies from previous calls will be preserved.
  • The other Cookies related methods are just mocked and do nothing: GetCookies, AddCookies, ClearCookies.
  • The following methods are also only mocked but do nothing: EnableResume, SetHttpVersion and SetMinimumTransferRate.
• The component roAppMemoryMonitor will only return measured data in Node.JS and Chromium browsers. For browsers the memory heap info only accounts for the main thread, as WebWorkers do not have support for performance.memory API.
• The roInput deep link events are supported, but the events related to Voice Commands are not.
• The roFileSystem is fully functional, but the message port events are not yet implemented.
• The complete Roku OS file system is available and shared among threads (main, render and tasks), with all volumes: pkg:, common:/, tmp:, cachefs: and ext1:. By default, the writeable volumes tmp: and cachefs: are limited to 32 MB each, see customization documentation to learn how to change those limits.
• The global functions Eval(), GetLastRunCompileError() and GetLastRunRuntimeError() are not available.
• The string mod cannot be used as variable or function parameter name, because it conflicts with remainder operator Mod (Roku devices allows that).
• Screensaver functionality is not yet implemented.
• SDK 1.0 deprecated components are not supported, but will be implemented in the future as a legacy apps preservation initiative.

Mocked Components and Libraries

• RAF (Roku Ads Framework) library with that exposes Roku_Ads is mocked with the most common methods available returning static values.
• RED (Roku Event Dispatcher) and Google IMA3 libraries are also mocked.
• Channel Store components (ChannelStore, roChannelStore and roChannelStoreEvent) are mocked with support for the fakeServer() feature.
• The roStreamSocket and roDataGramSocket components are mocked, and were only implemented to prevent crash on apps that use those.
• Several components have their methods and events mocked, they return constant values to prevent crash. Those are mostly related to device behaviors that are not possible to replicate in a browser environment or simply not applicable to the engine.

Out of Scope

• Roku OS User Interface.
• Roku Channel Store features.
• Video playback with Ads.