GTK: paint_with_z_index is broken

[xStrom]

paint_with_z_index internally calls into piet render_ctx.current_transform() which returns an unexpected value when running on Wayland. This can be seen in the anim example.

Piet internally seems to just call cairo_get_matrix so is this an issue with cairo on Wayland or what?

The returned matrix seems to have a static +26x / +60y translation added to it on Wayland. Indeed the GTK connect_draw handler receives a cairo context which has the following transform applied to it already: Affine([1.0, 0.0, 0.0, 1.0, 26.0, 60.0]).

Faulty behavior originally discovered by @Finnerale in #876.

[xStrom]

Okay I managed to reproduce the issue even with GTK on X11, so this isn't a Wayland specific issue or a GTK library bug. The issue can be reproduced on GTK/X11 by enabling debug_widget_id() on the multiwin example. The GTK menu system also applies a translate on the cairo context.

The current paint_with_z_index implementation doesn't work when there is a non-druid transform applied.

[xStrom]

This issue was fixed in piet#195. Druid will start behaving correctly whenever we update to piet 0.0.14.

[xStrom]

We've updated to piet 0.1.0 so this should be fixed now.