I'm getting a headache working with Gtk2::DrawingAreas. Seven headaches, to be
precise. Perhaps someone can offer some Perl paracetemol?
(As always, "Go away and read this document" or "Go away and read that code
example" would be terrific.)
I cobbled together a working example (drawarea.pl, attached). It opens a
Gtk2::Window with a Gtk2::DrawingArea inside it. There's a subroutine to draw a
rectangle inside the drawing area, and another to draw some pango markup text.
So far, so good.
1. I want to be able to detect mouse clicks. Specifically, I want to know when
the user clicks on one of the rectangles, so I can write some code to 'select'
the rectangle by changing its colour.
The example does half the job. The 'button-press-event' signal causes the
example to print the x/y coordinates of every mouse click.
Now, I need the user to be able to select *multiple* rectangles by clicking on
them while holding down the SHIFT or CTRL key. I don't know how to detect the
combination of mouse click + SHIFT/CTRL.
It's a pretty standard job - there must be an easy way to do it, right?
2. The 'button-press-event' signal doesn't help me with detecting
double-clicks. Is there a different signal for this?
3. I also want the user to be able to select multiple rectangles by dragging
the mouse across a portion of the DrawingArea.
Don't know what the technical term for this is - but the sequence is 'click on
position, hold down left mouse button, move mouse, release left mouse button'.
Again, a fairly standard job in graphics editing software, in which a rectangle
gets drawn (and updated) showing the area selected so far, before the mouse
button has been release.
The Gtk-Perl docs promise a simple graphic editor code example, but it's still
at the 'not written yet' stage. Can anyone point me in the right direction?
4. The call to Gtk2::Gdk::Drawable->draw_rectangle produces a rectangle that's
a different size, depending on whether it's filled in, or not.
(In the example, the filled-in blue rectangle is 1 pixel smaller in width and
in height, than the black rectangle. Actually, the blue rectangle is the one
that's the correct size.)
Is this really the expected behaviour of Gtk2::Gdk::Drawable->draw_rectangle?
It seems pretty odd to me.
5. I'm confused about how the pango text is drawn. Specifically, I want to be
able to draw in a font of a fixed size.
In the example, the line...
my $fontDescrip = Gtk2::Pango::FontDescription->from_string("Arial
12");
...doesn't cause text of 12 pixels to be drawn, not even if we change the call
to &drawPangoText to remove the 'size' attribute:
&drawPangoText(
$drawingArea,
150, 10,
"<span background = '#000000' foreground = '#FF0000'"
# . " size = '20000' weight = 'heavy'>Hello world!</span>" # This line
commented out
. " weight = 'heavy'>Hello world!</span>" # Replaced by this line
);
I can't find anything in the Gtk2-perl docs that give a clue about what 'size'
is doing. A value of about 500 seems to produce roughly the right size
characters, but heaven knows why. Where should I go from here?
6. Let's say that I use this code to draw a rectangle, and then draw some pango
text nearby.
Now let's say that the user clicks on the rectangle to 'select it', and I've
written some nice code to change the rectangle's colour. If, by any chance, the
pango text has been drawn ON TOP of the rectangle, I need to re-draw the pango
text, too.
It would be easy to do, if I knew that the pango text has filled a rectangle
starting at (x,y) of size (width, height). In the example, this is the area
that has been overdrawn with a black background.
I have not the slightest idea how to get these values. I wonder if anyone has
any ideas?
7. It's pretty easy to set up tooltips for a Gtk2::Button or Gtk2::Label, but I
haven't had any luck with the drawing area yet. I found a 'query_tooltip'
signal but I can't get it to work, nor can I find any perl scripts which do
this job.
Specifically, this modification to the example doesn't work:
# Drawing area signals
$drawingArea->set_events ([
'exposure-mask',
'leave-notify-mask',
'button-press-mask',
'pointer-motion-mask',
'pointer-motion-hint-mask',
]);
$drawingArea->signal_connect(query_tooltip => sub {
...
I'd like some kind of notification just before the tooltip appears, so I can
decide what text to display (namely, 'this is a blue rectangle!' or 'this is a
black rectangle!')
drawarea.pl
Description: Binary data
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