Question

I am new in pygtk. I am looking a way how to create custom widget which uses parent backgorund as its own background
something like this https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-prn1/31617_421363141269410_1875576801_n.jpg

How can I get parent bitmap and use it as its own bitmap?

class RoundRectPanel(gtk.DrawingArea, PanelBase):
    """
    Panel That represents
    """
    def __init__(self):
        super(ProximityPanel, self).__init__()

    def initialize(self):
        super(RoundRectPanel, self).initialize()

        self.set_size_request(340, 300)
        self.connect('expose-event', self.expose)

    def terminate(self):
        pass

    def rounded_rectangle(self, cr, x, y, w, h, r=20):
        #   A****BQ
        #  H      C
        #  *      *
        #  G      D
        #   F****E

        cr.move_to(x+r,y)                      # Move to A
        cr.line_to(x+w-r,y)                    # Straight line to B
        cr.curve_to(x+w,y,x+w,y,x+w,y+r)       # Curve to C, Control points are both at Q
        cr.line_to(x+w,y+h-r)                  # Move to D
        cr.curve_to(x+w,y+h,x+w,y+h,x+w-r,y+h) # Curve to E
        cr.line_to(x+r,y+h)                    # Line to F
        cr.curve_to(x,y+h,x,y+h,x,y+h-r)       # Curve to G
        cr.line_to(x,y+r)                      # Line to H
        cr.curve_to(x,y,x,y,x+r,y)             # Curve to A

    def expose(self, canvas, event):
        # Create cairo context
        cr = canvas.window.cairo_create()

        # TODO: 1. GET PARENT background
        # 2. set it as canvas background

        # 3. draw on it
        self.rounded_rectangle(cr, 0, 0, 340, 300)
        cr.stroke_preserve()
        cr.set_source_rgba(1.0, 1.0, 1.0, 0.5)
        cr.fill()

Answer 1

Currently found the workaround, which requires custom widget to communicate with his parent window (where the background image is drawn).
CustomWidget requires from parent information about background image (filename and imge location on the window)

class CustomWidget(gtk.DrawingArea):
def __init__(self, parent):
    super(CustomWidget, self).__init__()
    self.set_size_request(340, 300)
    self._parent = parent

    self.connect('expose-event', self._expose_event)

def _expose_event(self, widget, event):
    cr = widget.window.cairo_create()

    self.draw_context(cr, widget)

def draw_context(self, cr, widget):
    ctx = cr
    x, y, width, height = widget.allocation

    # parent window should have file name that is used as a background
    pixbuf = gtk.gdk.pixbuf_new_from_file(self._parent.file)
    ctx.save()
    # copy particular image region where your custom widget is located
    ctx.set_source_pixbuf(pixbuf, (-x) + self._parent.image.allocation.x, (-y) + self._parent.image.allocation.y)

    # draw background for custom widget
    ctx.paint()
    ctx.restore()

    # now draw what ever you want
    self.rounded_rectangle(cr, 0, 0, width, height)
    cr.set_line_width(1.0)
    cr.set_source_color(gtk.gdk.color_parse('grey'))
    cr.stroke_preserve()

    gradient = cairo.LinearGradient(width/2, 0, width/2, height)
    gradient.add_color_stop_rgba(0.00, 1, 1, 1, 0.9)
    gradient.add_color_stop_rgba(1.00, 0.4, 0.4, 0.4, 0.5)
    cr.set_source(gradient)
    cr.fill()