Own drag icon with same color and font settings as the default drag icon in a Gtk.TreeView - pygobject

Question

The Gtk.TreeView implements a default drag icon. It use the background color of the TreeView, it's font and the complete row-content as string.
I want the same (background-color, font-face, font-size, font-color) but with a shorter string (only the second of three columns).
In the example below create my own cairo.Surface to create such an icon. But color and font is a problem. I don't know how to set them up or (much more important) to ask the TreeView or Gtk itself for the current color and font values.
How does the TreeView get this values?
#!/usr/bin/env python3
import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk
from gi.repository import Gdk
import cairo
class MainWindow(Gtk.Window):
def __init__(self):
Gtk.Window.__init__(self, title="TreeView Drag and Drop")
self.connect("delete-event", Gtk.main_quit)
self.box = Gtk.Box()
self.add(self.box)
# "model" with dummy data
self.store = Gtk.TreeStore(int, str, int)
for i in range(5):
self.store.append(None, [i, 'Item {}'.format(i), i]) # treeview
self.tree = Gtk.TreeView(model=self.store)
self.box.pack_start(self.tree, True, True, 0)
# build columns
colA = Gtk.TreeViewColumn('Col A', Gtk.CellRendererText(), text=0)
self.tree.append_column(colA)
colB = Gtk.TreeViewColumn('Col B', Gtk.CellRendererText(), text=1)
self.tree.append_column(colB)
colC = Gtk.TreeViewColumn('Col C', Gtk.CellRendererText(), text=2)
self.tree.append_column(colC)
# enable default drag and drop
self.tree.set_reorderable(True)
# DnD events
self.tree.connect_after("drag-begin", self.drag_begin)
def drag_begin(self, widget, context):
model, path = widget.get_selection().get_selected_rows()
text = model[path][1]
# dummy surface/context
surface = cairo.ImageSurface(cairo.Format.RGB24, 0, 0)
cr = cairo.Context(surface)
# calculate text size
txtext = cr.text_extents(text)
width = int(txtext.width)
height = int(txtext.height)
offset = 10
# creal surface/context
surface = cairo.ImageSurface(cairo.Format.RGB24,
width + (offset*2),
height + (offset*2))
cr = cairo.Context(surface)
cr.set_source_rgb(1, 1, 1) # text color: white
cr.move_to(0+offset, height+offset)
cr.show_text(text)
# use the surface as drag icon
Gtk.drag_set_icon_surface(context, surface)
win = MainWindow()
win.show_all()
Gtk.main()
What I tried (but not worked) was cairo.Surface.create_similar()',cairo.Surface.create_similar_image()andGtk.TreeView.create_row_drag_icon()`.

Answer 1

This answer is based on a foreign mailing list posting.
The widget has a Gtk.StyleContext. A Pango.Layout is used to render the text based on the style informations in the Gtk.StyleContext.
def drag_begin(self, widget, context):
model, path = widget.get_selection().get_selected_rows()
text = model[path][1]
stylecontext = widget.get_style_context()
# new pango layout
pl = widget.create_pango_layout(text)
ink_rec, log_rect = pl.get_pixel_extents()
padding = 5
# create surface/context
surface = cairo.ImageSurface(cairo.Format.RGB24,
log_rect.width + (padding*2),
log_rect.height + (padding*2))
cr = cairo.Context(surface)
Gtk.render_background(stylecontext, cr, 0, 0,
log_rect.width + (padding*2),
log_rect.height + (padding*2))
Gtk.render_layout(stylecontext, cr, padding, padding, pl)
# border
line_width = cr.get_line_width()
cr.rectangle(-1+line_width, -1+line_width,
log_rect.width+(padding*2)-line_width,
log_rect.height+(padding*2)-line_width)
cr.stroke()
# use the surface as drag icon
Gtk.drag_set_icon_surface(context, surface)