As discussed in the following thread:
https://lists.freedesktop.org/archives/wayland-devel/2017-August/034755.html
the existing plane assignment in the DRM backend is vulnerable to
accidental masking of the intended fullscreen surface. This change
adds a simple stateful memory to the plane assignment algorithm
to prevent that.
---
libweston/compositor-drm.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/libweston/compositor-drm.c b/libweston/compositor-drm.c
index 8e1e788f..81dc8fe6 100644
--- a/libweston/compositor-drm.c
+++ b/libweston/compositor-drm.c
@@ -1495,6 +1495,7 @@ drm_assign_planes(struct weston_output *output_base, void
*repaint_data)
struct weston_view *ev, *next;
pixman_region32_t overlap, surface_overlap;
struct weston_plane *primary, *next_plane;
+ bool picked_scanout;
/*
* Find a surface for each sprite in the output using some heuristics:
@@ -1516,6 +1517,8 @@ drm_assign_planes(struct weston_output *output_base, void
*repaint_data)
output->cursor_plane.x = INT32_MIN;
output->cursor_plane.y = INT32_MIN;
+ picked_scanout = false;
+
wl_list_for_each_safe(ev, next, &output_base->compositor->view_list,
link) {
struct weston_surface *es = ev->surface;
@@ -1545,10 +1548,22 @@ drm_assign_planes(struct weston_output *output_base,
void *repaint_data)
next_plane = primary;
if (next_plane == NULL)
next_plane = drm_output_prepare_cursor_view(output, ev);
- if (next_plane == NULL)
+
+ /* If a higher-stacked view already got assigned to scanout,
it's incorrect to
+ * assign a subsequent (lower-stacked) view to scanout.
+ */
+ if (next_plane == NULL && !picked_scanout) {
next_plane = drm_output_prepare_scanout_view(output,
ev);
- if (next_plane == NULL)
+ if (next_plane)
+ picked_scanout = true;
+ }
+
+ /* Similarly, it's incorrect to elevate a view to an overlay if
some higher-stacked
+ * view is already identified as full-screen scanout.
+ */
+ if (next_plane == NULL && !picked_scanout)
next_plane = drm_output_prepare_overlay_view(output,
ev);
+
if (next_plane == NULL)
next_plane = primary;
--
2.13.3
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