PureBasic Forums - English

Posted: **Sun Feb 06, 2022 12:38 pm**

Hi,
I need to be able to read the vertical scroll position in a WebGadget and to move the scroll position in another WebGadget accordingy - I need those #PB_Web_ScrollY in GetGadgetAttribute() to work.

(The specific need is for a reader, to have two columns of content scrolling synchronized - two WebGadgets in the usual vertical scrolling, with the same content but offset.)

A previous recent search for the trick could not produce results. I am a bit rusty in managing GTK directly, so I may need a little help.

I suppose the documentation is that of [edit: no, see below] ; I will be checking it now.

Posted: **Sun Feb 06, 2022 3:39 pm**

One note: I had difficulties already identifying the documentation:

on my system, it seems what I should use is what in https://webkitgtk.org/ is the "Deprecated API Reference WebKit1", https://webkitgtk.org/reference/webkitg ... index.html , as I am finding the working functions there, instead of the "Stable API Reference WebKit2".

This as I had seen that for me and many other posters functions like webkit_web_settings_new() and webkit_web_view_load_string() worked, while apparently equivalent in the new documentation, webkit_settings_new() etc. gave "undefined reference" linker errors.

I think I will stick with the installed version, which most of us seem to be using, but the upgrade from WebKitGTK+ to WebKit2GTK seems to be possible directly with an install, see Shardik's post at https://www.purebasic.fr/english/viewto ... t2#p527097

Posted: **Sun Feb 06, 2022 4:23 pm**

In theory we are not far away; in practice, I can read the scroll position, but strangely cannot set it yet:

Code: Select all

ImportC "-lwebkitgtk-3.0"
	webkit_web_view_get_dom_document(*wkwv)		; WebKitWebView → WebKitDOMDocument
	webkit_dom_document_get_default_view(*wkdd)	; WebKitDOMDocument → WebKitDOMDOMWindow
	webkit_dom_dom_window_scroll_by(*wkddw, x.d, y.d)
	webkit_dom_dom_window_scroll_to(*wkddw, x.d, y.d)
	webkit_dom_dom_window_move_by(*wkddw, x.f, y.f)
	webkit_dom_dom_window_move_to(*wkddw, x.f, y.f)
	webkit_dom_dom_window_get_scroll_y(*wkddw)
EndImport

s.s = "Lorem ipsum felicitas sit amet. "
s="<p>"+s+s+s+s+"</p>"+#LF$+"<p>"+s+s+"</p>"+#LF$+"<p>"+s+s+s+"</p>"
For a=0 To 9
	html.s = html+"<h1>Section #"+a+"</h1>"+s+"<hr/>"+#LF$
Next

OpenWindow(0,0,0,800,600,"Test")
WebGadget(0,0,0,800,600,"")

SetGadgetItemText(0,#PB_Web_HtmlCode,html)

*wkdd  = webkit_web_view_get_dom_document(GadgetID(0)) : Debug *wkdd
*wkddw = webkit_dom_document_get_default_view(*wkdd)   : Debug *wkddw

webkit_dom_dom_window_move_to(*wkddw, 0.0, 1000.0)

Repeat
   EvID = WaitWindowEvent()
   ypos = webkit_dom_dom_window_get_scroll_y(*wkddw)
   If ypos<>old_ypos : Debug "> ypos: "+ypos : old_ypos=ypos : EndIf
Until EvID=#PB_Event_CloseWindow

Edit: probably because the value parameters of are in fact of type 'gfloat'? From other examples, 'int' can be used for 'gint'... Again, the documentation for gfloat, gdouble etc. is not immediately found with a search.

Posted: **Sun Feb 06, 2022 4:45 pm**

It depends on which Linux version you are using.
Therefore you must also use the library functions.
- Up to Ubuntu 18.04 : libwebkitgtk-3.0
- From Ubuntu 20.04 : libwebkit2gtk-4.0

Only with PB v6.00 (20.04) the Webkit 2 (only gtk3) is supported.

Posted: **Sun Feb 06, 2022 5:45 pm**

mk-soft wrote: Sun Feb 06, 2022 4:45 pm with PB v6.00 (20.04) the Webkit 2 (only gtk3) is supported.

With the new PB, I see, the version the new API, WebKit2GTK, will have to be used, and new techniques adopted for the scrolling.

Nonetheless, it would be nice to make this one work, for completeness... Reading the scrolling position works; setting it does not.

Edit: also because:

-- I just tried the #PB_Web_ScrollY attribute on the PB 6.00 beta, and it does not work;

-- I checked the documentation index for WebKit2GTK ( https://webkitgtk.org/reference/webkit2 ... x-all.html ) to find information about scrolling, position, and moving, and nothing evident appears... It must be hidden in some obscure part

Posted: **Sun Feb 06, 2022 7:27 pm**

Incidentally: I also tried the "JavaScriptCore" way, as suggested by the API documentation, and I interpreted that as meaning "using JSEvaluateScript()".

Code: Select all

ImportC "-lwebkitgtk-3.0"
	webkit_web_view_get_dom_document(*wkwv)					; WebKitWebView → WebKitDOMDocument
	webkit_dom_document_get_default_view(*wkdd)				; WebKitDOMDocument → WebKitDOMDOMWindow
	webkit_dom_dom_window_scroll_by(*wkddw, x.d, y.d)
	webkit_dom_dom_window_scroll_to(*wkddw, x.d, y.d)
	webkit_dom_dom_window_move_by(*wkddw, x.f, y.f)
	webkit_dom_dom_window_move_to(*wkddw, x.f, y.f)
	webkit_dom_dom_window_get_scroll_y(*wkddw)
	;webkit_web_view_get_javascript_global_context(*wkwv)	; WebKitWebView → JSGlobalContextRef
	webkit_web_view_get_main_frame(*wkwv)						; WebKitWebView → WebKitWebFrame
	webkit_web_frame_get_global_context(*wkwf)				; WebKitWebFrame → JSGlobalContextRef
EndImport

ImportC ""
	JSEvaluateScript(*ctx, *script, *thisObject, *sourceURL, startingLineNumber, *exception)
	;Pointer ctx, Pointer script, Pointer thisObject, Pointer sourceURL, int startingLineNumber, Pointer<Pointer> exception
	JSStringCreateWithUTF8CString(*s)
EndImport

s.s = "Lorem ipsum felicitas sit amet. "
s="<p>"+s+s+s+s+"</p>"+#LF$+"<p>"+s+s+"</p>"+#LF$+"<p>"+s+s+s+"</p>"
For a=0 To 9
	html.s = html+"<h1>Section #"+a+"</h1>"+s+"<hr/>"+#LF$
Next

OpenWindow(0,0,0,800,600,"Test")
WebGadget(0,0,0,800,600,"")

SetGadgetItemText(0,#PB_Web_HtmlCode,html)

*wkwf  = webkit_web_view_get_main_frame(GadgetID(0))		: Debug *wkwf
*jsgcr = webkit_web_frame_get_global_context(*wkwf) 		: Debug *jsgcr


Debug JSEvaluateScript(*jsgcr,JSStringCreateWithUTF8CString("window.scrollTo(0,1000);"),#Null,#Null,1,#Null)

Repeat
   EvID = WaitWindowEvent()
Until EvID=#PB_Event_CloseWindow

It does not work. There is a chance that I am using a bad syntax on JSEvaluateScript...

There may be also a chance that those commands require JavaScript to be enabled on the WebGadget for JavaScriptCore to work? In that case: no, never. Javascript has to remain disabled for security: it's a reader one simply needs. There must be no need for the WebGadget to process scripts /inside/ its "web contents", to achieve something as simple as scrolling. Not sure this is the case, but...

Edit: ...but I suspect it is not the case of "enabling javascript in the WebGadget", because I tried an

Code: Select all

JSEvaluateScript(*jsgcr,JSStringCreateWithUTF8CString("document.body.style.background = '#ACE'"),#Null,#Null,0,#Null)

and it equally does not work.

Posted: **Sun Feb 06, 2022 9:11 pm**

I have extended my modules for the WebGadget with RunJavaScript. It works
JavaScript 'window.scrollTo(0,500);'

Show Module: WebGadget Extension (PB v6.00 GTK3) and Mini Browser Example

Posted: **Sun Feb 06, 2022 9:29 pm**

mk-soft wrote: Sun Feb 06, 2022 9:11 pm I have extended my modules for the WebGadget with RunJavaScript. It works

Thank you Mk-Soft,
it will surely be useful to extend functionality on PB6.xx, libraries webkit2gtk-4.0. Also because, I read that the multithreading feature of webkit2gtk make it a mess... By the way: can you use those javascript functions while keeping the webgadget in "disabled javascript" state?

There should be a solution though for the traditional libraries, PB 5.73... It should be much simpler than its successor!

Posted: **Sun Feb 06, 2022 9:37 pm**

I tried the third way, and again no good result but it's there, close...

In theory, the traditional WebGadget should be wrapped inside a GtkScrolledWindow (what allows the scrollbars in that version of GTK), and gtk_scrolled_window_get_vadjustment should return a GtkAdjustment which contains the scrolling. To the best of my understanding.

Now, the way below does not work, but I can see it, in memory, the value is there, changing before my eyes as I scroll,

if I check the memory at range between *ga-128 and *ga+128 ¹ it is within a structure right above, looks like a float ², it's there exactly at *ga-92, and I cannot get what it is part of...

Edit: also, said scroll value is 16 bytes after the result of gtk_adjustment_get_value(*ga) - that "get value" should return it, and instead it is two "longs or doubles" later...

It must not be the gtk_widget_get_parent(GadgetID(0)) that reaches the right window... Need to get from the WebKitWebView which is the WebGadget to its right GtkScrolledWindow...

( ¹ *ga being the vadjustment of the parent of the WebGadget... )
(² well, it should be a double, according to specifications, at *ga-96 - whatever... )

Code: Select all

ImportC ""
	gtk_scrolled_window_get_vadjustment( *scrolled_window )	; GtkScrolledWindow* → GtkAdjustment*
	gtk_widget_get_parent( *widget )			; GtkWidget → GtkWidget
	gtk_adjustment_get_value(*adjustment)	; GtkAdjustment → gdouble
	gtk_adjustment_get_upper(*adjustment)	; GtkAdjustment → gdouble
EndImport

s.s = "Lorem ipsum felicitas sit amet. "
s="<p>"+s+s+s+s+"</p>"+#LF$+"<p>"+s+s+"</p>"+#LF$+"<p>"+s+s+s+"</p>"
For a=0 To 9
	html.s = html+"<h1>Section #"+a+"</h1>"+s+"<hr/>"+#LF$
Next

OpenWindow(0,0,0,800,600,"Test")
WebGadget(0,0,0,800,600,"")

SetGadgetItemText(0,#PB_Web_HtmlCode,html)


*scrolledwin = gtk_widget_get_parent(GadgetID(0)) 		: Debug *scrolledwin


*ga = gtk_scrolled_window_get_vadjustment(*scrolledwin) : Debug *ga
ypos.d = PeekD(gtk_adjustment_get_value(*ga)) : Debug ypos
uppr.d = PeekD(gtk_adjustment_get_upper(*ga)) : Debug uppr
   
Repeat
   EvID = WaitWindowEvent()
   
Until EvID=#PB_Event_CloseWindow

Posted: **Sun Feb 06, 2022 11:14 pm**

it will surely be useful to extend functionality on PB6.xx, libraries webkit2gtk-4.0. Also because, I read that the multithreading feature of webkit2gtk make it a mess...

The 'multithreading feature' is a bit annoying.
It took me a long time to figure out why the thread for reading the content of the webgadget didn't start.
You can no longer wait for the callback with a semaphore in the same call to read the webgadget content. The thread only starts when the call is exited. And then the callback comes.

By the way: can you use those javascript functions while keeping the webgadget in "disabled javascript" state?

I don't known, but I think not

Posted: **Sun Feb 06, 2022 11:31 pm**

mk-soft wrote: Sun Feb 06, 2022 11:14 pm
By the way: can you use those javascript functions while keeping the webgadget in "disabled javascript" state?
I don't known, but I think not

Well, that would be a critical issue. It would be like being able to load a page, but, js being disabled, not being able to scroll or zoom. But anyway, it should be verified. It's just that in these mindless times of internet-connected shoes I am scared in advance.

Posted: **Mon Feb 07, 2022 12:57 am**

I friggin' made it, with the "GtkAdjustment vadjustment of GtkScrolledWindow" way, and it's been a #@!# journey.

So, webkit_dom_dom_window_get_scroll_y() works, but webkit_dom_dom_window_move_to() and similar do not; whereas
gtk_adjustment_get_value() does not, but gtk_adjustment_set_value() and gtk_scrolled_window_set_vadjustment() do. So,

Code: Select all

ImportC "-lwebkitgtk-3.0"
	webkit_web_view_get_dom_document(*wkwv)		; WebKitWebView → WebKitDOMDocument
	webkit_dom_document_get_default_view(*wkdd)	; WebKitDOMDocument → WebKitDOMDOMWindow
	webkit_dom_dom_window_get_scroll_y(*wkddw)
EndImport

ImportC ""
	gtk_scrolled_window_get_vadjustment( *scrolled_window )	; GtkScrolledWindow* → GtkAdjustment*
	gtk_widget_get_parent( *widget )			; GtkWidget → GtkWidget
	gtk_adjustment_set_value(*adjustment, v.d)	; GtkAdjustment → gdouble
	gtk_scrolled_window_set_vadjustment (*scrolled_window, *vadjustment)
EndImport

s.s = "Lorem ipsum felicitas sit amet. "
s="<p>"+s+s+s+s+"</p>"+#LF$+"<p>"+s+s+"</p>"+#LF$+"<p>"+s+s+s+"</p>"
For a=0 To 9
	html.s = html+"<h1>Section #"+a+"</h1>"+s+"<hr/>"+#LF$
Next

OpenWindow(0,0,0,800,600,"Test")
WebGadget(   0,  0,40,800,560,"")
ButtonGadget(1,  0, 0,400, 40,"<")
ButtonGadget(2,400, 0,400, 40,">")

SetGadgetItemText(0,#PB_Web_HtmlCode,html)

*wkdd  = webkit_web_view_get_dom_document(GadgetID(0)) : Debug *wkdd
*wkddw = webkit_dom_document_get_default_view(*wkdd)   : Debug *wkddw

*scrolledwin = gtk_widget_get_parent(GadgetID(0)) 	: Debug *scrolledwin
*ga = gtk_scrolled_window_get_vadjustment(*scrolledwin) : Debug *ga

Repeat
   EvID = WaitWindowEvent()
	
   Select EvID
      Case #PB_Event_Gadget
	      EvG = EventGadget()
	         Select EvG
					Case 1
						ypos = webkit_dom_dom_window_get_scroll_y(*wkddw)
						gtk_adjustment_set_value(*ga,ypos-100.0)
						gtk_scrolled_window_set_vadjustment(*scrolledwin, *ga)
					Case 2
						ypos = webkit_dom_dom_window_get_scroll_y(*wkddw)
						gtk_adjustment_set_value(*ga,ypos+100.0)
						gtk_scrolled_window_set_vadjustment(*scrolledwin, *ga)
						
				EndSelect
			
	EndSelect
Until EvID=#PB_Event_CloseWindow

Meanwhile, to reach that, I have seen the strangest things: gtk_adjustment_get_value(), gtk_adjustment_get_upper() etc. should return double precision values directly: instead, they all return a pointer - the same pointer -, and that pointer is 16 bytes before the actual type-double value. The source code for GtkAdjustment is at https://gitlab.gnome.org/GNOME/gtk/-/bl ... justment.c , and I do not know how such behaviour is explained.

Posted: **Mon Feb 07, 2022 1:53 am**

So, by the way, the "multicolumn with scroll" effect I intended would be along the lines of

Code: Select all

ImportC "-lwebkitgtk-3.0"
	webkit_web_view_get_dom_document(*wkwv)		; WebKitWebView → WebKitDOMDocument
	webkit_dom_document_get_default_view(*wkdd)	; WebKitDOMDocument → WebKitDOMDOMWindow
	webkit_dom_dom_window_get_scroll_y(*wkddw)
EndImport

ImportC ""
	gtk_scrolled_window_get_vadjustment( *scrolled_window )	; GtkScrolledWindow* → GtkAdjustment*
	gtk_widget_get_parent( *widget )			; GtkWidget → GtkWidget
	gtk_adjustment_set_value(*adjustment, v.d)	; GtkAdjustment → gdouble
	gtk_scrolled_window_set_vadjustment (*scrolled_window, *vadjustment)
EndImport

s.s = "Lorem ipsum felicitas sit amet. "
s="<p>"+s+s+s+s+"</p>"+#LF$+"<p>"+s+s+"</p>"+#LF$+"<p>"+s+s+s+"</p>"
For a=0 To 9
	html.s = html+"<h1>Section #"+a+"</h1>"+s+"<hr/>"+#LF$
Next

OpenWindow(0,0,0,1280,960,"Test",#PB_Window_ScreenCentered)
WebGadget(0,  0,0,640,960,"")
WebGadget(1,640,0,640,960,"")

SetGadgetItemText(0,#PB_Web_HtmlCode,html)
SetGadgetItemText(1,#PB_Web_HtmlCode,html)

*wkdd0  = webkit_web_view_get_dom_document(GadgetID(0)) : Debug *wkdd0
*wkddw0 = webkit_dom_document_get_default_view(*wkdd0)  : Debug *wkddw0

*wkdd1  = webkit_web_view_get_dom_document(GadgetID(1)) : Debug *wkdd1
*wkddw1 = webkit_dom_document_get_default_view(*wkdd1)  : Debug *wkddw1

*sdw0 = gtk_widget_get_parent(GadgetID(0)) 			: Debug *sdw0
*ga0 = gtk_scrolled_window_get_vadjustment(*sdw0) 	: Debug *ga0

*sdw1 = gtk_widget_get_parent(GadgetID(1)) 			: Debug *sdw1
*ga1 = gtk_scrolled_window_get_vadjustment(*sdw1) 	: Debug *ga1

HideGadget(1,1) : is_yettostart=1
Repeat
   EvID = WaitWindowEvent()
   
   ypos0 = webkit_dom_dom_window_get_scroll_y(*wkddw0)
   If ypos0<>oldypos
		If is_yettostart : HideGadget(1,0) : is_yettostart=0 : EndIf
		gtk_adjustment_set_value(*ga1,ypos0+960.0)
		gtk_scrolled_window_set_vadjustment(*sw1, *ga1)
		oldypos=ypos
	EndIf
	
	
   Select EvID
      Case #PB_Event_Gadget
	      EvG = EventGadget()
	         Select EvG
					
						
				EndSelect
			
	EndSelect
Until EvID=#PB_Event_CloseWindow

with some polishing of the effect still pending.

Posted: **Mon Feb 07, 2022 3:08 pm**

And this is an example of the desired effect - which honestly works quite well, functionally and graphically. So, it may be deserving a pic.

https://ibb.co/D550y7H

Posted: **Mon Feb 07, 2022 7:30 pm**

Does not run under Ubuntu 20.04/21.04 because the libwebkitgtk-3.0-dev is no longer available.

PureBasic Forums - English

Get and set scroll position in WebGadget

Get and set scroll position in WebGadget

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Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget

Re: Get and set scroll position in WebGadget