Fix direct scan-out flickering

Sometimes when using direct scan-out, some flickering between the
fullscreen app and the regular desktop could be seen.

This happened because we called wlr_output_attach_render and then
wlr_output_attach_buffer for direct scan-out. wlr_output_attach_render
makes the OpenGL context current but also attaches the OpenGL buffer to
the primary plane apparently (all of this happens inside
eglMakeCurrent).

This patch moves the scan-out logic outside of output_render, before
wlr_output_attach_render. This lines it up with rootston's
implementation. This also makes more sense since no rendering is
involved when using direct scan-out.

Sorry about that, I should've tested this with more clients. The new
code has been tested with mpv and a GLFW demo.

1 files changed, 96 insertions, 0 deletions

diff --git a/sway/desktop/output.c b/sway/desktop/output.c
index 4bfc3b77..7f250542 100644
--- a/sway/desktop/output.c
+++ b/sway/desktop/output.c
@@ -412,6 +412,72 @@ static void send_frame_done(struct sway_output *output, struct timespec *when) {
         output_for_each_surface(output, send_frame_done_iterator, when);
 }
 
+static void count_surface_iterator(struct sway_output *output,
+                struct wlr_surface *surface, struct wlr_box *_box, float rotation,
+                void *data) {
+        size_t *n = data;
+        (*n)++;
+}
+
+static bool scan_out_fullscreen_view(struct sway_output *output,
+                struct sway_view *view) {
+        struct wlr_output *wlr_output = output->wlr_output;
+        struct sway_workspace *workspace = output->current.active_workspace;
+        if (!sway_assert(workspace, "Expected an active workspace")) {
+                return false;
+        }
+
+        if (view->saved_buffer) {
+                return false;
+        }
+
+        for (int i = 0; i < workspace->current.floating->length; ++i) {
+                struct sway_container *floater =
+                        workspace->current.floating->items[i];
+                if (container_is_transient_for(floater, view->container)) {
+                        return false;
+                }
+        }
+
+#if HAVE_XWAYLAND
+        if (!wl_list_empty(&root->xwayland_unmanaged)) {
+                return false;
+        }
+#endif
+
+        if (!wl_list_empty(&output->layers[ZWLR_LAYER_SHELL_V1_LAYER_OVERLAY])) {
+                return false;
+        }
+        if (!wl_list_empty(&root->drag_icons)) {
+                return false;
+        }
+
+        struct wlr_surface *surface = view->surface;
+        if (surface == NULL) {
+                return false;
+        }
+        size_t n_surfaces = 0;
+        output_view_for_each_surface(output, view,
+                count_surface_iterator, &n_surfaces);
+        if (n_surfaces != 1) {
+                return false;
+        }
+
+        if (surface->buffer == NULL) {
+                return false;
+        }
+
+        if ((float)surface->current.scale != wlr_output->scale ||
+                        surface->current.transform != wlr_output->transform) {
+                return false;
+        }
+
+        if (!wlr_output_attach_buffer(wlr_output, surface->buffer)) {
+                return false;
+        }
+        return wlr_output_commit(wlr_output);
+}
+
 static void damage_handle_frame(struct wl_listener *listener, void *data) {
         struct sway_output *output =
                 wl_container_of(listener, output, damage_frame);
@@ -422,6 +488,35 @@ static void damage_handle_frame(struct wl_listener *listener, void *data) {
         struct timespec now;
         clock_gettime(CLOCK_MONOTONIC, &now);
 
+        struct sway_workspace *workspace = output->current.active_workspace;
+        if (workspace == NULL) {
+                return;
+        }
+
+        struct sway_container *fullscreen_con = root->fullscreen_global;
+        if (!fullscreen_con) {
+                fullscreen_con = workspace->current.fullscreen;
+        }
+
+        if (fullscreen_con && fullscreen_con->view) {
+                // Try to scan-out the fullscreen view
+                static bool last_scanned_out = false;
+                bool scanned_out =
+                        scan_out_fullscreen_view(output, fullscreen_con->view);
+
+                if (scanned_out && !last_scanned_out) {
+                        sway_log(SWAY_DEBUG, "Scanning out fullscreen view");
+                }
+                if (last_scanned_out && !scanned_out) {
+                        sway_log(SWAY_DEBUG, "Stopping fullscreen view scan out");
+                }
+                last_scanned_out = scanned_out;
+
+                if (scanned_out) {
+                        goto frame_done;
+                }
+        }
+
         bool needs_frame;
         pixman_region32_t damage;
         pixman_region32_init(&damage);
@@ -436,6 +531,7 @@ static void damage_handle_frame(struct wl_listener *listener, void *data) {
 
         pixman_region32_fini(&damage);
 
+frame_done:
         // Send frame done to all visible surfaces
         send_frame_done(output, &now);
 }