Hi,
I'm fairly new at gtkmm, and wish to clarify what I think is happening when a
Gtk::DrawingArea is used.
The issue I've been prodding at is that the Cairo surface is obtained (as far
as I can make out) by using a RefPtr to the window being drawn on. When the
Cairo surface is the only object in that window, that works fine; however, if
there are any other objects created in the same class as the DrawingArea, they
get drawn over.
For example, if I modify the clock example, adding a button to the display
works fine if it is created and added in the main function.
If I modify the Clock class constructor to put the additional widgets in
there(see below for code), they seem to get drawn over when the on_expose_event
method is called.
My guess is that the DrawingArea selected within the on_expose_event is the
size of the widget the entire class is constructed in, as it appears to ignore
the widget the Drawing Area is created within if there are other widgets in the
class. I'm stumped as to whether it's determined within the Gtk::Allocation or
on creation of the Cairo::Context, and can't find any examples around giving an
alternative way of getting a context. The only way I can see to workaround it
is to ensure the Drawing Area is in a separate class of its own, as that seems
to keep the window the size of the widget it _should_ be assigned to.
Glib::RefPtr<Gdk::Window> window = get_window();
if(window){
Gtk::Allocation allocation = get_allocation(); //this appears to only
get dimensions after the window size has been passed. Is this right?
const int width = allocation.get_width();
const int height = allocation.get_height();
Cairo::RefPtr<Cairo::Context> cr = window->create_cairo_context();//
this appears to be where the drawing area obtains it's dimensions. So the
window size is determined where?
My questions:
Am I missing something obvious (yet again...)?
Is there another way of creating a DrawingArea that allows more explicit
defining of the surface?
Am I right about where the surface size comes from?
modified section of clock.h:
#ifndef GTKMM_EXAMPLE_CLOCK_H
#define GTKMM_EXAMPLE_CLOCK_H
#include <gtkmm/drawingarea.h>
#include <gtkmm/window.h>
#include <cairomm/context.h>
/*added to draw additional widgets: */
#include <gtkmm/box.h>
#include <gtkmm/button.h>
class Clock : public Gtk::Window
{
public:
Clock();
virtual ~Clock();
protected:
//Override default signal handler:
virtual bool on_expose_event(GdkEventExpose* event);
bool on_timeout();
double m_radius;
double m_line_width;
Gtk::DrawingArea clocksquare;
Gtk::HBox OuterBox, middlebox;
Gtk::Button button;
};
and then within clock.cc:
#include <ctime>
#include <math.h>
#include "clock.h"
Clock::Clock()
: m_radius(0.42), m_line_width(0.05),
middlebox(),
clocksquare(),
button("Hello!")
{
set_title("Cairomm Clock");
set_size_request(450,150);
middlebox.set_size_request(100, 150);
add(OuterBox);
OuterBox.pack_end(clocksquare, Gtk::PACK_SHRINK);
OuterBox.pack_start(button);
OuterBox.pack_start(middlebox, Gtk::PACK_SHRINK);
show_all_children();
NB this example simply shows what happens when things don't work.
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