getting visible area of Tk::Scrolled?

halley has asked for the wisdom of the Perl Monks concerning the following question:

I am playing around some more with Tk::Canvas, and in particular, the scrolled variety. The scrollbar mechanisms seem really primitive.

    my $c = $parent->Scrolled('Canvas',
                  -width  => $width,
                  -height => $height,
                  -background => 'beige',
                  -scrollbars => 'osoe',
                  -scrollregion => [ 0, 0, $width, $height ]);
[download]

I've constructed a Scrolled Canvas, which apparently returns a ref of type Tk::Frame. That must have the children, including a Canvas and a couple of Scrollbars.

I also found the Tk::Autoscroll class, which didn't come with my build of Perl/Tk, but was easy enough to add.

When dragging around an item in a large scrolled canvas, I want to auto-scroll to keep the dragged item in view. This doesn't seem so hard, except knowing where the scroller is viewing at the current time.

I can't figure out the way to go from a blessed Canvas ref (given in the drag events), to calculate or query the area of the scrollregion that is currently visible.

Before I go digging farther, I bet someone already has some code that calculates the visible area.

--
[ e d @ h a l l e y . c c ]

Comment on getting visible area of Tk::Scrolled? Download Code

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Re: getting visible area of Tk::Scrolled? by zentara (Archbishop) on Sep 16, 2011 at 20:21 UTC
You may be looking for $canvas->bbox('all'), also see Two questions regarding -tk-canvas #!/usr/bin/perl use Tk; use Tk::Canvas; use Tk::Label; my $mw = tkinit(-title, 'Canvas'); $mw->geometry('250x500'); my $frame = $mw->Frame(-width, 250, -height, 250)->pack(-fill, 'both', + -expand,1); my $canvas = $frame->Scrolled('Canvas', -width, 300, -height, 300, -bg=>'white', -scrollbars, 'osoe' )->pack(-fill,'both',-expand,1); my $btn = $mw->Button(-text, "Add Stuff", -command,\&addStuff) ->pack(); my $btn1 = $mw->Button(-text, "Add More Stuff", -command,\&addmoreStuf +f) ->pack(); MainLoop; sub addStuff{ $canvas->createText(500, 500, -text, "Some text @ 500, 500." ); $canvas->createRectangle( 50, 50, 110, 110, -fill, 'red'); $canvas->createRectangle( 150, 150, 210, 210, -fill, 'green'); $canvas->createRectangle( 250, 250, 310, 310, -fill, 'blue'); $canvas->createText(20, 20, -text, "Some text @ 20, 20." ); # # Your can use an array for your bounding box # commented out to show both ways to set the scrollregion # Just make sure you are 1 less on lower right and bottom # Or you will have out of bounds array... easy to forget # if you don't use a frame with your canvas $canvas->configure(-scrollregion => [ 0, 0, 599, 599]); # $canvas->configure(-scrollregion => [$canvas->bbox('all')]); } sub addmoreStuff{ $canvas->createText(1500, 1500, -text, "Some text @ 1500, 1500." ); $canvas->createRectangle( 5000, 5000, 1100, 1100, -fill, 'red'); $canvas->createRectangle( 1500, 1500, 2100, 2100, -fill, 'green'); $canvas->createRectangle( 2500, 2500, 3100, 3100, -fill, 'blue'); $canvas->createText(2000, 10, -text, "Some text @ 2000, 10." ); # # Your can use an array for your bounding box # commented out to show both ways to set the scrollregion # Just make sure you are 1 less on lower right and bottom # Or you will have out of bounds array... easy to forget # if you don't use a frame with your canvas #$canvas->configure(-scrollregion => [ 0, 0, 599, 599]); $canvas->configure(-scrollregion => [$canvas->bbox('all')]); } [download] I'm not really a human, but I play one on earth. Old Perl Programmer Haiku ................... flash japh	[reply] [d/l]
Re: getting visible area of Tk::Scrolled? by BrowserUk (Patriarch) on Sep 16, 2011 at 19:05 UTC
To find the canvas coordinate that is currently being displayed at the top left corner of the canvas window, use: `my $canvasTLx = $canvas->canvasx( 0 ); my $canvasTLy = $canvas->canvasy( 0 );` [download] See also the `-confine` & `-scrollregion` options to the canvas widget. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re^2: getting visible area of Tk::Scrolled? by halley (Prior) on Sep 17, 2011 at 12:52 UTC
Partly there. What are the screen X, Y of the lower right corner of the canvas window? Accurately taking into account whether scrollbars have appeared or not? -- `[ e d @ h a l l e y . c c ]`	[reply]
Re^3: getting visible area of Tk::Scrolled? by BrowserUk (Patriarch) on Sep 17, 2011 at 13:06 UTC
Use `$canvas->get_corners` to obtain the bounding box of the visible portion of the canvas. See also the return lists from the `->xview()` & `->yview()` methods which are useful for manipulating the scrollbars. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re^4: getting visible area of Tk::Scrolled? by halley (Prior) on Sep 19, 2011 at 20:42 UTC


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