This is useful for debugging offloading without having to rely
on gstreamer giving us dmabufs. To use it, set
GDK_DEBUG=force-offload
in the environment.
Allow to specify a D₂ transform when attaching a texture to a
subsurface, to handle flipped and rotated content. The Wayland
implementation handles these transforms by setting a buffer
transform on the subsurface.
All callers have been updated to pass GDK_TEXTURE_TRANSFORM_NORMAL.
This will let us use a subset of the full texture, which can
be necessary in the case that converters put padding around
content in dmabufs. The naming follows the Wayland viewporter
spec.
For now, make all callers pass the full texture rect.
We are going to introduce another rect, so better to be clear in
naming. We are following the naming of the Wayland viewporter spec
and call the rectangle that we drawing into the dest(ination).
We accept transparent subsurfaces for passthrough now, when they are
above the surface.
But we did not unset the opaque region to empty when the texture is
transprent.
Sadly, subsurface positioning is undefined in this case. We'll
trust the compositor to not mess up if the device coordinates
after applying the scale are integral, but otherwise, we'll
decline.
Instead, do it all in attach(), which becomes more and more like
ConfigureWindow. This is good, because it will let us take the
above-ness into account when making decisions about attaching.
There was one branch in the success case that turned it into a failure,
yet we were still reporting a success (and discarding the buffer).
Don't do that.
