Currently the DRM backend ends up picking the bottom-most view which meets all the checks for eligibility, for direct scanout usage. If more than one such view exists, we get a visual result counter to expectations -- it should be the highest-sorted such view that the user sees.
The big loop in drm_assign_planes() that assigns views to planes iterates top-down through the weston_layer's, and the particular way that the results are progressively stored in variables means that if more than one pass through the loop encounters a view which is fullscreen and opaque then the last (bottom-most) of these passes is the one whose results are preserved upon exit from the loop. This normally isn't a problem because mostly only the desktop shell has a notion of fullscreen surfaces. desktop-shell takes care (whether intentionally or not I can't tell) that when running full-screen only the logical topmost view is actively left in a visible weston_layer. Is it informally expected that the shell must not allow more than one fullscreen view at a time? Would there be interest in a patch to drm_assign_planes() that adds a bit more awareness to the plane assignment so that only the topmost fullscreen opaque view is picked for scanout?
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