We're about the merge the Direct3D backend into package gpu. Extract the
raw Direct3D API to its own package, just like package glimpl.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
NewDevice creates a Device given an API, which is the necessary GPU
resources for a backend.
Convert gpu.New to take an API instead of a backend.Device directly.
In turn, this frees us to later unexport the backend package along with
the backend implementations (for now just gioui.org/gpu/gl for OpenGL).
It also allows programs that embed Gio (such as gioui.org/example/glfw)
to freely choose a backend, not just OpenGL.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Completing the goal of allowing foreign Direct3D contexts for our
D3D backend, slim down the constructor to take only the device handle.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Elias Naur