Hi;
On 30 December 2016 at 11:15, Sergei Kolomeeyets <kolomeeyets@xxxxxxxxx> wrote:
> Hi, everyone
> I'm struggling with migration from gtk2. Well gtk_cairo_create is deprecated
> in gtk3. And it looks the changes are very serious (or I'm sach silly that
> even do not understand what should I do instead of it ). Is there anybody
> who use Drawing Area in GTK3 and can explain the right way of its cairo
> context creation and drawing on it to me. It would be so appreciated.
Connect to the GtkWidget::draw signal (or subclass GtkDrawingArea and
override the GtkWidgetClass.draw virtual function, which is
essentially the same) and use the Cairo context that's given to you.
Drawing *on widgets* outside of their rendering cycle is not possible
in GTK+ 3.x.
If you want to draw something off screen and then composite it inside
your widget, you'll need to create a Cairo surface yourself, using
something like:
GdkWindow *window = gtk_widget_get_window (widget);
cairo_surface_t *surface = gdk_window_create_similar_surface
(window, CAIRO_CONTENT_COLOR_ALPHA, width, height);
then create a Cairo context from it, and draw:
cairo_t *cr = cairo_create (surface);
// draw
cairo_destroy (cr);
Now you can use the surface as a source on the Cairo context that
GtkWIdget::draw gives you:
static gboolean
on_draw (GtkWidget *widget, cairo_t *cr)
{
// render your surface on the widget's context
cairo_set_source_surface (cr, surface, x, y);
cairo_paint (cr);
// do your own drawing
}
> Documentation says the following:
> ***gtk_cairo_create
> gdk_cairo_create has been deprecated since version 3.22 and should not be
> used in newly-written code. Use gdk_window_begin_draw_frame() and
> gdk_drawing_context_get_cairo_context() instead.
This is only needed if you're literally implementing a toolkit (like
GTK) on top of GDK.
> gboolean draw_callback(GtkWidget *area, GdkEventExpose *event, GArray
> *ptLinePoints) {
> ...
> cairo_t *cr = gdk_drawing_context_get_cairo_context (area);
> ...
> }
This is *not* a GtkWidget::draw callback. You should read the API reference:
https://developer.gnome.org/gtk3/stable/GtkWidget.html#GtkWidget-draw
The second argument of the callback is a Cairo context; use it.
> But linker (gcc package) writes "undefined reference to
> `gdk_drawing_context_get_cairo_context"... :-(
> Everything indicated that I missed several lines of code before
> gdk_drawing_context_get_cairo_context. But what lines exactly? Googling
> gives nothing...
It means you're not using GTK+ 3.22, but likely an earlier version.
In any case, you should just forget about the drawing context, and use
the Cairo context that GTK itself gives you.
Ciao,
Emmanuele.
--
https://www.bassi.io
[@] ebassi [@gmail.com]
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