Qt Blog

Some time ago I published a couple of blog posts talking about Qt WebGL Streaming plugin. The time has come, and the plugin is finally merged into the Qt repository. In the meantime, I worked on stabilization, performance and reducing the calls sent over the network. It also changed a bit in the way the connections are handled.

New client approach

In the previous implementations, the client was accepting more than one concurrent connections. After the latest changes, the plugin is going to behave like a standard QPA plugin. Now, only one user per process is allowed. If another user tries to connect to the web server, it will see a fancy loading screen until the previous client disconnects.
The previous approach caused some problems with how the desktop applications and GUI frameworks are designed. Everyone can agree that desktop applications are not intended to work with concurrent physical users, even if the window instances were different for all users.

No more boilerplate code

Previously the application had to be modified to support this platform plugin. This code was needed to make the application work with the plugin:

class EventFilter : public QObject
{
public:
    virtual bool eventFilter(QObject *watched, QEvent *event) override
    {
        Q_UNUSED(watched);
        if (event->type() == QEvent::User + 100) {
            createWindow(true);
            return true;
        } else if (event->type() == QEvent::User + 101) {
            window->close();
            window->deleteLater();
            return true;
        }

        return false;
    }
};

And install the event filter into the QGuiApplication.

No more modifications in applications are needed anymore.

How to try

So, if you want to give it a try before Qt 5.10 is released (~November 2017) do the following:

Prerequisites

Since WebGL was modelled using OpenGLES2 as reference, first thing you will need is to have an OpenGLES2 version of Qt built. To do that, you need to pass the parameter -opengl es2 to the configure before building.
Example:

./configure -opensource -confirm-license -opengl es2

Depending on your system it is possible you will need some aditional headers and libraries to be able to use es2.

Testing the plugin

After building everything, you can try to run a Qt Quick example.

To try the photoviewer example we need to build it and run with the -platform webgl parameters:

./photoviewer -platform webgl

If you want to try the Qt Quick Controls 2 Text Editor:

./texteditor -platform webgl

Supported options

Currently, the plugin only supports an option to configure the port used by the embedded HTTP Server. If you want to listen in the default HTTP port you should write -platform webgl:port=80.

The future

The plugin will be part of Qt 5.10 release as a technology preview (TP), as it needs to be improved. Currently, the plugin contains an HTTP Server and a Web Sockets server to handle the browser connections. I’m planning to remove the servers from the plugin and start using a Lightweight QtHttpServer we are working on right now. Once it’s ready, you will be able to create an application server to launch different process inheriting the web socket to communicate with the browsers. This will allow for supporting more than one concurrent user instead of sharing applications among users.

Note: The plugin only works using the Threaded Render Loop. If you use Windows or a platform using a different render loop ensure you set QSG_RENDER_LOOP environment variable to threaded

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