Re: Getting the visible portion of a scrolled window

On Wed, 2008-05-21 at 12:29 -0400, Lindley M French wrote:
> I figured out what I needed, but it was bizarrely difficult. I first
> had to use gtk_bin_get_child on the scrolled window to get the
> viewport; then I had to use gdk_window_get_position() on
> viewport->bin_window to get the (negative) x and y coordinates of the
> visible region, then gdk_window_get_size() on viewport->view_window to
> get the width and height of the visible region.
> There *must* be a better way do get this information...

Not quite what you're up against, but a similar scenario: we've recently
been poking away at GtkTextView and friends; it turns out that there are
four optional GdkWindows surrounding the central one that displays the
text. You use functions like gtk_text_view_buffer_to_window_coords() to
take the GtkTextView's idea of where a point in the overall text canvas
and translate it into a vertical or horizontal component so you can
figure out what co-ordinates to move a child Widget you've placed in
that such a side GdkWindow.

As I was working with it, I found that the conversion would give
positive answers larger than the viewport if the location was scrolled
off the viewport below, and *negative* answers if the location was
scrolled off the thing above.

At first, I was surprised by this, but upon reflection it makes sense.
If you place a 30 pixel high widget at position -15, then you only want
to show half of it. GDK appears to clip it on this basis and properly
only showed half of it. If you get -300 back, well, you're scrolled
significantly further into your GtkTetxView, and so, surprise, you're
side bar child widget now needs to be off the screen - I was a bit wary
of passing said -300 along as a co-ordinate, but GDK seems smart enough
to Do The Right Thing™ and just not draw the child.

Anyway, this is all very voodoo, but it does seem another example of
negative co-ordinates showing up, and perhaps makes you feel you're not
the only one :)

In case you have no idea what I'm referring to, you might start with


Andrew Frederick Cowie

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