Re: Dragging a TreeViewItem painted with custom CellRenderer

[Dirk Vanden Boer <dirk vdb gmail com>]

On Mon, Apr 6, 2009 at 2:43 PM, Dirk Vanden Boer <dirk vdb gmail com> wrote:
> Hi,
>
> I have written a custom CellRenderer that displays a Gdk::Pixbuf and
> some text using Pango::Layout.
> Everything seems to work fine but when I try to drag an item in the
> TreeView I see assertion failures in the console and no text is
> displayed in the item that gets dragged around.
>
> Assertion failures:
> (gejengel:9508): Gdk-CRITICAL **: gdk_drawable_get_depth: assertion
> `GDK_IS_DRAWABLE (drawable)' failed
> (gejengel:9508): Gtk-CRITICAL **: gtk_paint_layout: assertion
> `style->depth == gdk_drawable_get_depth (window)' failed
>
> Is there something I am missing here? Do I need to do something
> special when a drag is initiated?
>
> The source code of my CellRenderer can be found at:
> http://code.google.com/p/gejengel/source/browse/trunk/src/ui/cellrendererplayqueue.cpp
>
> Best Regards,
> Dirk
>

I did some more digging and have found the cause of the problem:
In the render function I cast the Gdk::Drawable that is passed as a
function argument to a Gdk::Window because the paint_layout method of
the current style requires Gdk::Window.

Now I noticed that when I start dragging a cell the dynamic cast to
Gdk::Window fails, I then tried to cast it to a Gdk::Pixmap and that
worked like a charm. So during a drag the cell is not rendered to a
Gdk::Window but to a Gdk::Pixmap.

So in stead of calling widget.get_style()->paint_layout I call
pixmap->draw_layout to draw directly to the pixmap.

But isn't there an api call missing in Gtk::Style of Gtkmm that
accepts a Gdk::Pixmap in stead of Gdk::Window, because painting the
text on a pixmap using the widget style is possible using the c api.

gtk_paint_layout (widget.get_style()->gobj(), window->gobj(),
GTK_STATE_NORMAL, TRUE, const_cast<GdkRectangle*>(exposeArea.gobj()),
widget.gobj(), "cellrendererplayqueue", cellArea.get_x() + (3 * xPad)
+ ALBUM_ART_WIDTH + xOffset, cellArea.get_y() + yPad, layout->gobj());

Regards,
Dirk