[webkit-gtk] Can I get viewport image cahanges from draw event.

[Miha]

On 07/02/2014 09:46 AM, Miha wrote:
> Hi
>
> I am developing an eInk paper based application. I have the server 
> that runs webkit2gtk based applications and eInk devices that are 
> connected to server via WiFi. Basically server renders image changes 
> and sends them to device. User can use devices touchscreen to send 
> click events to server.
>
> The thing I want to do, but I don't know if it is possible, is to get 
> viewport changes from draw signal.
> I want to get changed regions and image pixels from those regions 
> because don't want to do full screen refreshes eInk display if it is 
> not necessary.
>
> As I understand I could do something like this, but I do not know how 
> to do it exactly.
> http://pastebin.com/1L8cNFfJ (my test application)
>
> 1. Something is changed and need to be drawn.
> Breakpoint 2, WebKit::PageClientImpl::setViewNeedsDisplay 
> (this=0x78c670, rect=...)
>     at ../Source/WebKit2/UIProcess/API/gtk/PageClientImpl.cpp:77
> 77        gtk_widget_queue_draw_area(m_viewWidget, rect.x(), rect.y(), 
> rect.width(), rect.height());
>
> 2. WebKit Ui process draws changes to WebKitWebView widget cairo context.
> Breakpoint 1, webkitWebViewBaseDraw (widget=0x782490, cr=0x7d3d80)
>     at ../Source/WebKit2/UIProcess/API/gtk/WebKitWebViewBase.cpp:409
>
> 3. Custom "draw" signal handler is triggered in application. I get 
> cairo context as parameter. Can I render changes from 1. here? Is it 
> possible? How to do it?
> 2014-07-01T11:54:51.499118Z web_view draw 1 {X: 150.000000, Y: 
> 80.000000, W: 450.000000, H:225.000000} 
> 0x0-d41d8cd98f00b204e9800998ecf8427e
> 2014-07-01T11:54:51.499175Z window draw 1 {X: 150.000000, Y: 
> 80.000000, W: 450.000000, H:225.000000} 
> 0x0-d41d8cd98f00b204e9800998ecf8427e
>
> Breakpoint 1, webkitWebViewBaseDraw (widget=0x782490, cr=0x7d3d80)
>     at ../Source/WebKit2/UIProcess/API/gtk/WebKitWebViewBase.cpp:409
> 409    {
> (gdb) c
> Continuing.
> 2014-07-01T11:54:51.899118Z web_view draw 1 {X: 150.000000, Y: 
> 80.000000, W: 450.000000, H:225.000000} 
> 0x0-d41d8cd98f00b204e9800998ecf8427e
>
>
>
>
> I am curious , why are there two web_view draw events for each change? 
> What trigers the second call to webkitWebViewBaseDraw and sends the 
> second web_view "draw" signal in point 3?
> I there way to avoid this? Maybe I can use window "draw" as it is 
> triggered only once?
>
> Thank you for answer.
> Best
>
> Miha
>
>
>
>
Hi

I would relay appreciate, if somebody would help me clear out details. 
Please.

Best
Miha
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