[Development] Though about rich text (html, WebView) rendering

[Fabrice Salvaire]

Hi Kai,

Le 26/02/2016 11:15, Koehne Kai a écrit :
>
>> -----Original Message-----
>> From: Development [mailto:development-
>> bounces+kai.koehne=theqtcompany.com at qt-project.org] On Behalf Of
>> Fabrice Salvaire
>> Sent: Thursday, February 25, 2016 1:33 PM
>> To: development at qt-project.org
>> Subject: [Development] Though about rich text (html, WebView) rendering
>>
>> Dear all,
>>
>> I am investigating to port a content server to an off-line mobile application
>> in order to don't rely to a network connection at all. Thus I have to port a
>> database, a kind of web framework, a template engine and a rendering
>> engine. I believe it can be a use of case of Qt on mobile platform.
>>
>> If we consider HTML is the right way to display rich text there is actually to
>> solution with Qt : Text for basic HTML and WebView for a full compliance. I
>> am not sure to understand why we cannot use WebEngine on mobile
>> platform. WebEngine seems more interesting since it provides WebChannel
>> hooks.
> Let's be clear here on the terminology: With "WebView" I assume you refer
> to Qt WebView (http://doc.qt.io/qt-5/qtwebview-index.html), which on Android
> integrates the native browser. Since Qt WebChannel can use WebSockets as
> a means of communciation, you can use it with Qt WebView on Android, too.
> You'd need to set up a local websocket server though ("ws://localhost/...").
> Not sure how exactly that works for an Android app.

Ok, I could investigate this.

>
> Qt WebEngine is indeed currently only supported for Windows, OS X and
> Linux. Porting it to Android is possible, but a lot of work.

Thus android and ios don't forbid it.

>> I succeed to hack the WebView using the loadingChanged signal in order to
>> simulate a dynamic HTML framework, i.e. call loadHtml according to the url.
>> But I don't known if it is the right way to achieve this. Maybe we can extend
>> the Java wrapper for this purpose? The fact the rendering surface is a light
>> web browser behind the scene can be disturbing since it doesn't integrate
>> very well with the QML application.
> I'm not sure I really understood what you've been doing with the loadingChanged
> Signal.

What I did basically to catch page loading and set the content according 
to the url ( WebView get page -> LoadingChanged signal -> call loadHtml 
-> ... ) :

     function handle_loading(load_request) {
         if (load_request.url == "qrc:/index.html" && 
load_request.status == 0) {
             var html_content = "<h1>Main Page</h1><p><a 
href=\"page1\">A link</a></p>";
         }
         if (load_request.url == "qrc:/page1" && load_request.status == 0) {
             var html_content = "<h1>Basic HTML</h1>";
         }
         var base_url = "qrc:/";
         web_view.loadHtml(html_content, base_url)
     }

     WebView {
         id: web_view
         objectName: "web_view"
         anchors.fill: parent
         url: "qrc:/index.html"
         onLoadingChanged: handle_loading(loadRequest)
     }

>> I think there is something evil since a Web engine is a concurrent of QML.
> What do you mean by that?

I am just thinking how to implement the power of HTML for text rendering 
in QML cleverly. And don't use any web framework for mobile platform.

Mathjax is a good example. How can we implement a computer algebra 
system //using Qt for example ?

>   
>> We can render math formulas out of the box using a QML WebView and
>> mathjax, but we can also implement a full application using HTML5 and
>> javascript. Thus use a stack over a stack ...
>>
>> What is the future plan and advices for this topic?
> I'm afraid there are no direct plans to support Qt WebEngine on Android.
> If I'd be you I'd try to set up a WebSocket. If that ain't possible you could
> Still try to communicate between the WebView and your app
> just via runJavaScript().
>
> Regards
>
> Kai

Fabrice
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