Center image area on window about drawing HOT 7 OPEN

	def on_draw(self, area, cairo_context):
		"""Signal callback. Executed when self.drawing_area is redrawn."""

		surface = self.get_surface()

		allocation = self.get_allocation()
		width = allocation.width
		height = allocation.height
		image_width = surface.get_width()
		image_height = surface.get_height()

		# Fill background with a color
		cairo_context.new_path()
		cairo_context.set_source_rgb(1, 0, 0)
		cairo_context.move_to(0, 0)
		cairo_context.rel_line_to(height, 0)
		cairo_context.rel_line_to(height, width)
		cairo_context.rel_line_to(0, width)
		cairo_context.close_path()
		cairo_context.fill()
		cairo_context.paint()

		# Draw the image on top
		cairo_context.translate((width / 2) - (image_width / 2), (height / 2) - (image_height / 2))
		cairo_context.scale(self.zoom_level, self.zoom_level)
		cairo_context.set_source_surface(surface, \
		                                 -1 * self.scroll_x, -1 * self.scroll_y)
		cairo_context.paint()

		self.active_tool().on_draw(area, cairo_context)

		event_x, event_y = self.get_event_coords(event)
		allocation = self.get_allocation()
		width = allocation.width
		height = allocation.height
		surface_width = self.surface.get_width()
		surface_height = self.surface.get_height()
		event_x -= (width - surface_width) / 2
		event_y -= (height - surface_height) / 2