The current approach makes use of
- A tiled rendering to work around gdk_texture_diff only doing pointer
comparaison
- Assumes that we would only recieve a scanout cmd followed by multiple
flush ones
In reality, with virtio-gpu at least, the scanout cmd is always
submitted followed by a flush one containing the damaged region.
With the assumption currently made, we end up creating a new paintable
for every scanout cmd causing a full redraw instead
of only redrawing the damaged areas.
Isntead we create the paintable once and call import whenever
we receive a flush cmd (UpdateDMABUF) so we can properly
pass the damage area when creating a GdkGLTexture making
the tiled rendering no longer needed.
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