silly cairo surface scaling example (dd 2017-07-03 requires patched pycairo)

cairo_surface_scaling.py

import gi
gi.require_version("Gtk", "3.0")
from gi.repository import Gtk
import cairo

class IconWindow(Gtk.Window):
    def __init__(self, *args, **kwargs):
        super().__init__(default_width=150, default_height=150, **kwargs)

        self.icon_name = "thunderbird-icon"
        self._image = Gtk.Image()
        self.grid = Gtk.Grid()
        self.add(self.grid)
        self.grid.add(self._image)

        
        self._icon_theme = Gtk.IconTheme.get_default()
        self.connect("style-set", self._on_style_set)
        self._set_icon()

        self.connect("delete-event", Gtk.main_quit)

    @property
    def device_scale(self):
        scale = self.get_scale_factor()
        return (scale, scale)

    def _get_icon_surface(self, icon_name, size=48):
        surface = self._icon_theme.load_surface(
            icon_name, size, 1, self.get_window(),
            Gtk.IconLookupFlags.FORCE_SIZE
        )
        surface.set_device_scale(*self.device_scale)
        return surface
        
    def _set_icon(self):
        x_scale, y_scale = self.device_scale
        
        surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, 48, 48)
        surface.set_device_scale(x_scale, y_scale)
        context = cairo.Context(surface)
        
        main_surface = self._get_icon_surface(self.icon_name)
        context.set_source_surface(main_surface, 0, 0)
        context.paint()

        mini_one = self._get_icon_surface(self.icon_name, 16)
        context.set_source_surface(mini_one, 1 / x_scale, 1 / y_scale)
        context.paint()
        
        mini_two = self._get_icon_surface(self.icon_name, 16)

        # Paint one pixel from the bottom
        height = surface.get_height()
        mini_height = mini_two.get_height()
        y = height / y_scale - mini_height / y_scale - 1 / y_scale
        print("height: %s / mini height: %s / y: %s" % (height, mini_height, y))

        # Paint one pixel from the right
        width = surface.get_width()
        mini_width = mini_two.get_width()
        x = width / x_scale - mini_height / x_scale - 1 / x_scale
        print("width: %s / mini width: %s / x: %s" % (width, mini_width, x))
        
        context.set_source_surface(mini_two, x, y)
        context.paint()

        self._image.set_from_surface(surface)

    def _on_style_set(self, *args, **kwargs):
        print(*args, **kwargs)

my_win = IconWindow()
my_win.show_all()

Gtk.main()