Re: Gtk::Image, Gtk::ImageSurface, Cairo::Context, Gtk::Pixbuf : how to combine?

[Yann Leydier <yann leydier info>]

Hi,

as there is a version of Gdk::Pixbuf::create_from_data() that takes a 
destroyer for the data as argument, it is highly probable that you have 
to make sure that the data is not destroyed before the pixbuf. In this 
case, the data is destroyed at the end of paint_image() and not 
available anymore when the expose event is thrown.

Usually, people use a DrawingArea with Cairo, not an Image. This allows 
to draw directly on the DrawingArea's Gdk::Window via Cairo.

yann

On 08/02/13 16:08, jody wrote:
> Hi
>
> What i want to do is to get a cairo context to draw in, and then
> somehow get a pixbuf which i can use to fill a Gtk::Image.
> Here's how i do it:
> - create an ImageSurface,
> - get its Cairo::Context,
> - draw into the Context
> - create a Pixbuf from th ImageSurface (which now should hold the
> drawing made via the Context
> - call the Gtk::Image's set-method with the PixBuf
> But that way i get a Segmenrtation fault.
>
> In particular, I have an application with a Gtk::Window containing a
> Gtk::Image (m_imgMain).
> When a button is pressed, i call the window's method paint_image
> (which does the steps described above):
>
> void XLoopWin::paint_image() {
>      // get current size of image
>      Gtk::Allocation allocation = m_imgMain.get_allocation();
>      const int iW = allocation.get_width();
>      const int iH = allocation.get_height();
>
>      // create  image surface
>      Cairo::RefPtr<Cairo::ImageSurface> surface =
>          Cairo::ImageSurface::create(Cairo::FORMAT_ARGB32, iW, iH);
>
>      // create a context to draw on
>      Cairo::RefPtr<Cairo::Context> cr = Cairo::Context::create(surface);
>
>      // here i would draw in the cr, but have crash without drawing
>
>       // create a Pixbuf from the ImageSurface
>       Glib::RefPtr<Gdk::Pixbuf> pixbuf = Gdk::Pixbuf::create_from_data(
>           surface->get_data(), Gdk::COLORSPACE_RGB, true, 8, iW, iH,
> surface->get_stride());
>
>      // set the drawing
>      m_imgMain.set(pixbuf);
>
>      // make sure image is redrawn
>      m_imgMain.queue_draw();
> }
>
>
> This method completes, but immediately afterwards i have a
> Segmentation fault deep down
>
> #0  0x00007ffff5fb9227 in gdk_cairo_set_source_pixbuf ()
>     from /usr/lib64/libgdk-3.so.0
> #1  0x00007ffff68c51d7 in gtk_theming_engine_render_icon ()
>     from /usr/lib64/libgtk-3.so.0
> #2  0x00007ffff6888333 in gtk_render_icon () from /usr/lib64/libgtk-3.so.0
> #3  0x00007ffff67e88ef in _gtk_icon_helper_draw ()
>     from /usr/lib64/libgtk-3.so.0
> #4  0x00007ffff67f72c9 in gtk_image_draw () from /usr/lib64/libgtk-3.so.0
> #5  0x00007ffff7a8372c in
> Gtk::Widget_Class::draw_callback(_GtkWidget*, _cairo*) () from
> /usr/lib64/libgtkmm-3.0.so.1
> ...
> #43 0x00007ffff478c3ac in g_main_loop_run () from /usr/lib64/libglib-2.0.so.0
> #44 0x00007ffff680eda2 in gtk_main () from /usr/lib64/libgtk-3.so.0
> #45 0x00007ffff7a2b047 in Gtk::Main::run(Gtk::Window&) ()
>     from /usr/lib64/libgtkmm-3.0.so.1
> #46 0x0000000000406897 in main (iArgC=1, apArgV=0x7fffffffddd8) at XLoop.cpp:18
>
>
> Can anybody tell me the correct way to do this?
>
> Thank You
>    Jody
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