[webkit-gtk] rendering a webpage to SVG

[Carlos Garcia Campos]

El vie, 21-08-2020 a las 10:45 +0200, Ivan Klimek escribió:
> Hi Carlos,
> 
> thanks for your fast reply
> 
> not sure if this helps or if your question was addressed to me - from
> my *very* limited understanding - how its done its done in Qt - they
> have the qt_svg module that implements methods that directly write
> vectorized SVG elements:
> 
> void drawEllipse(const QRectF &r) override;
>  void drawPath(const QPainterPath &path) override;
>  void drawPixmap(const QRectF &r, const QPixmap &pm, const QRectF
> &sr) override;
>  void drawPolygon(const QPointF *points, int pointCount,
> PolygonDrawMode mode) override;
>  void drawRects(const QRectF *rects, int rectCount) override;
>  void drawTextItem(const QPointF &pt, const QTextItem &item)
> override;
>  void drawImage(const QRectF &r, const QImage &pm, const QRectF &sr,
>  Qt::ImageConversionFlags flags = Qt::AutoColor) override;
> 
> see here: 
> https://github.com/qt/qtsvg/blob/dev/src/svg/qsvggenerator.cpp
> 
> from code its used like this:
> 
>     QWebFrame *frame = m_page.mainFrame();
>     QPainter painter;
>     QSvgGenerator svg;
> 
>     svg.setFileName(fileName);
>     svg.setSize(resolution);
> 
>     painter.begin(&svg);
> 
>     frame->render(&painter);
> 
> and that's all - output is vector SVG - every text / formatting etc
> all vector

Is that QtWebKit using WebKit1 or WebKit2?

> cairo is able to draw to SVG vectorized too, but the surface types
> need to be set correctly when drawing, I took a very light look at
> webkit-gtk cairo usage and cairo surface types are image types / aka
> bitmap so it draws stuff already to bitmap, and once in bitmap there
> is no way back :( but maybe I am reading this wrong, not sure
> 
> *I do not know why this is done the way it is done in webkit-gtk,
> maybe it would be possible to just internally use svg surfaces?* 
> 
> would be epic if webkit-gtk could do something like that as Qt Webkit
> is dead and there are so many projects using this ... 
> 
> Thanks
> Ivan
> 
> 
> On Fri, Aug 21, 2020 at 1:57 AM Carlos Alberto Lopez Perez <
> clopez at igalia.com> wrote:
> > On 20/08/2020 12:24, Ivan Klimek wrote:
> > > Dear webkit-gtk developers,
> > > 
> > > I am trying to render a webpage to SVG, I am successful in doing
> > so
> > > using Qt webkit - but as you all know Qt webkit has been
> > discontinued
> > > thus I am trying to migrate my code to webkit GTK
> > > 
> > > the problem I am facing is that the generated SVG is only a
> > wrapped PNG
> > > image of the rendered webpage, on Qt the webpage is rendered "all
> > > vector" texts etc all is "vectorized" an example of using this
> > approach
> > > are apps like: http://cutycapt.sourceforge.net/ or 
> > https://wkhtmltopdf.org/
> > > 
> > > my code is as follows (parts omitted for brevity):
> > > 
> > > g_signal_connect(main_window, "damage-event",
> > G_CALLBACK(capture),
> > > main_window);
> > > 
> > > static gboolean capture(GtkWidget *widget, GdkEvent *event,
> > gpointer
> > > user_data)
> > > {
> > >    
> > >   fprintf(stderr, "damage event callback called..\n");
> > > 
> > >   cairo_surface_t *surface =
> > >
> > gtk_offscreen_window_get_surface(GTK_OFFSCREEN_WINDOW(user_data));
> > > 
> > 
> > Instead of getting the cairo surface from GTK, you can use the
> > WebKitGTK
> > API directly with the functions webkit_web_view_get_snapshot*
> > 
> > Years ago I wrote a simple program that generates a png image from
> > a
> > webpage with that. Check it here: https://github.com/clopez/wksnap
> > 
> > I tried now to use your example code to generate a svg image
> > instead of
> > a png one [1], but I'm getting the same issue you comment of it
> > generating a svg image that is embedding a png one.
> > 
> > I'm unsure how to fix that. My limited understanding is that once
> > you
> > get the cairo surface from webkit, that surface is already a bitmap
> > surface.. so I'm unsure if is possible to convert that back to a
> > vector
> > surface. I wonder how QtWebKit did this??
> > 
> > 
> > Hope this helps.
> > Regards
> > 
> > 
> > [1] test patch to apply over wksnap: http://ix.io/2uLb
> > 
> 
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-- 
Carlos Garcia Campos
http://pgp.rediris.es:11371/pks/lookup?op=get&search=0xF3D322D0EC4582C3
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