Almost all our linear gradients have 2 stops.
Add a simple shader for that case.

If the current clip is entirely contained in
the outline of an outset shadow, we don't need
to draw anything.

Recognize the rounded-clip-with-color-inside situation
and do manual nine-slicing for it to minimize the number
of pixels send through clipping shaders.

This roughly counts how many pixels we feed through
each fragment shader.

inspector: Fix surface transform regression

See merge request GNOME/gtk!3280

Ever since we added surface-to-widget transforms,
the autofading of the fps overlay did not work anymore,
since it was given the transient transform node, most
of the time.

Fix this by passing both the root of the node tree and
the node for the toplevel widget to prepare_render, and
hande the widget node to the overlays. Update the
affected overlays that need to have their positioning
adjusted.

(cherry picked from commit f33a2febc7df6ec9c7721361f94121c2db079057)

Wip/otte/for master

See merge request GNOME/gtk!3279

We were leaking buffers. This wasn't caught by valgrind and friends
because it was shared memory (with the compositor), but top(1) would
instantly see memory consumption of the app and the shell go through the
roof.

We were calling _gdk_surface_update_size() every frame, even if the
window size didn't change. This would cause us to discard all cached
buffers and redraw the whole screen.

This was BAD.