[perl-win32-gui-users] Drawing (Part 1) [Was: Refreshing the Window]

[Robert M. <rob...@us...>]

On 30/05/07, George <sir...@ya...> wrote:
> thanks for the response,  but where should we  insert the invalidate
> function,
>  i am lost completely. and many discussions in the forum are complicated and
> for experts only, i have tried many variations with no success. the
> available examples in the forum are calling a sub paint which includes the
> drawing functions inside it ,and it happend the drawing functions are
> speedy, but suppose a function are drawing a fractal and this is a time
> consuming, then we will see that this approach is unpractical,  we just want
> to refresh the points of color ,and not to recalculate the code everytime we
> move or hide the window.

Unfortunately drawing using the Win32 API, and understanding all the
gotchas is not trivial.  This is not helped by the way that Win32::GUI
exposes the 'Paint' event.  I've had it on my list of things to
investigate further for some time, and you've spurred me into looking
at it in a bit more detail.  As a result, I'm not sure how to improve
things in a backewards-compatible way.  While I think about it some
more, here's the first of 2 examples.  This example takes the
traditional approach of doing all the painting in the 'Paint' handler,
determining what to draw, and drawing it, each time the handler is
called.

I'll follow-up with a second example showing how to create a memory DC
as a backing store that you only need to draw into when things change.

Hope it is useful.
Regards,
Rob.

#!perl -w
use strict;
use warnings;

use Win32::GUI qw( CW_USEDEFAULT RDW_VALIDATE RDW_NOCHILDREN );

my $do_drawing = 0;

my $mw = Win32::GUI::Window->new(
	-title => 'Draw on click example',
    -left => CW_USEDEFAULT,
	-size  => [ 400, 300 ],
    -onPaint => \&paint,
);

$mw->AddButton(
    -text => _get_button_text(),
    -pos  => [150,150],
    -onClick => \&click,
);

$mw->Show();
Win32::GUI::Dialog();
$mw->Hide();
exit(0);

sub paint {
	my ($self, $dc) = @_;

    # This Save() and the final Restore() are one way
    # to ensure the DC is returned to Win32 in the same
    # state as when we got it.
    my $saved = $dc->Save();

    # Win32::GUI doesnt use BeginPaint()/EndPaint() for the
    # DC it passes to its Paint handler.  Here we approximate
    # what BeginPaint does:
    # (1) Calling GetUpdateRect with FLAG=1 causes the background
    #     of the invalidated area t be cleared (WM_ERASEBKGND sent),
    #     and invalid non-client area to be repainted (WM_NCPAINT sent).
    # (2) Convert the update rect to a region and select it into the
    #     DC - set up the correct clipping area for us (this is not strictly
    #     necessary, but will help reduce re-draw flicker
    # (3) We validate the DC.  We do this using Window->Redraw() rather than
    #     DC->Validate(), as validating the entire DC validates child windows,
    #     stopping them being repainted (unless we give the main window
    #     the WS_CLIPCHILDREN style).
    {
        # Erase background, repaint non-client area and get update rect
        my($l, $t, $r, $b) = $dc->GetUpdateRect(1);

        # GetUpdateRect can return undef if there is no update region -
        # generally a Paint event only happens if there is a non-empty
        # update region, but it can happen if there are 'internal' paint
        # events being generated.
        if(defined $l) {
            my $clip_rgn = Win32::GUI::Region->CreateRectRgn($l, $t, $r, $b);
            $dc->SelectClipRgn($clip_rgn);
        }

        # Validate the whole window
        $self->Redraw(RDW_VALIDATE | RDW_NOCHILDREN);
    }

    # Eventually .... do our drawing
    if($do_drawing) {
        $dc->Rectangle(10,10,100,100);
    }

    # Restore the DC to the state it was in before we got it
    $dc->Restore();

	return 1;
}

sub click {
    my ($self) = @_;

    $do_drawing = !$do_drawing;

    $self->Text(_get_button_text());

    $self->GetParent->InvalidateRect(1);

    return 1;
}

sub _get_button_text {
    return $do_drawing ? 'Hide ...' : 'Draw ...';
}
__END__