[PATCH 2/3] compositor: recompute output position on mode switch

[David Fort]

When an output permanently changes its resolution, the output on the right
should be moved accordingly. We also add an event for output resizing so that
plugins can react when an output is resized.

Signed-off-by: David Fort <contact at hardening-consulting.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
---
 src/compositor.c | 35 +++++++++++++++++++++++++----------
 src/compositor.h |  1 +
 2 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/src/compositor.c b/src/compositor.c
index b6ef7f3..37fdd0c 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -143,6 +143,11 @@ static void weston_mode_switch_finish(struct weston_output *output,
 	}
 }
 
+
+static void
+weston_compositor_reflow_outputs(struct weston_compositor *compositor,
+				struct weston_output *resized_output, int delta_width);
+
 WL_EXPORT int
 weston_output_mode_set_native(struct weston_output *output,
 			      struct weston_mode *mode,
@@ -150,6 +155,7 @@ weston_output_mode_set_native(struct weston_output *output,
 {
 	int ret;
 	int mode_changed = 0, scale_changed = 0;
+	int32_t old_width;
 
 	if (!output->switch_mode)
 		return -1;
@@ -165,11 +171,17 @@ weston_output_mode_set_native(struct weston_output *output,
 		}
 	}
 
+	old_width = output->width;
 	output->native_mode = mode;
 	output->native_scale = scale;
 
 	weston_mode_switch_finish(output, mode_changed, scale_changed);
 
+	if (mode_changed || scale_changed) {
+		weston_compositor_reflow_outputs(output->compositor, output, output->width - old_width);
+
+		wl_signal_emit(&output->compositor->output_resized_signal, output);
+	}
 	return 0;
 }
 
@@ -4062,23 +4074,25 @@ bind_output(struct wl_client *client,
 		wl_output_send_done(resource);
 }
 
-/* Move other outputs when one is removed so the space remains contiguos. */
+/* Move other outputs when one is resized so the space remains contiguous. */
 static void
-weston_compositor_remove_output(struct weston_compositor *compositor,
-				struct weston_output *remove_output)
+weston_compositor_reflow_outputs(struct weston_compositor *compositor,
+				struct weston_output *resized_output, int delta_width)
 {
 	struct weston_output *output;
-	int offset = 0;
+	bool start_resizing = false;
+
+	if (!delta_width)
+		return;
 
 	wl_list_for_each(output, &compositor->output_list, link) {
-		if (output == remove_output) {
-			offset = output->width;
+		if (output == resized_output) {
+			start_resizing = true;
 			continue;
 		}
 
-		if (offset > 0) {
-			weston_output_move(output,
-					   output->x - offset, output->y);
+		if (start_resizing) {
+			weston_output_move(output, output->x + delta_width, output->y);
 			output->dirty = 1;
 		}
 	}
@@ -4101,7 +4115,7 @@ weston_output_destroy(struct weston_output *output)
 
 	weston_presentation_feedback_discard_list(&output->feedback_list);
 
-	weston_compositor_remove_output(output->compositor, output);
+	weston_compositor_reflow_outputs(output->compositor, output, output->width);
 	wl_list_remove(&output->link);
 
 	wl_signal_emit(&output->compositor->output_destroyed_signal, output);
@@ -4704,6 +4718,7 @@ weston_compositor_create(struct wl_display *display, void *user_data)
 	wl_signal_init(&ec->output_created_signal);
 	wl_signal_init(&ec->output_destroyed_signal);
 	wl_signal_init(&ec->output_moved_signal);
+	wl_signal_init(&ec->output_resized_signal);
 	wl_signal_init(&ec->session_signal);
 	ec->session_active = 1;
 
diff --git a/src/compositor.h b/src/compositor.h
index 0bbf458..7c6d7d9 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -744,6 +744,7 @@ struct weston_compositor {
 	struct wl_signal output_created_signal;
 	struct wl_signal output_destroyed_signal;
 	struct wl_signal output_moved_signal;
+	struct wl_signal output_resized_signal; /* callback argument: resized output */
 
 	struct wl_signal session_signal;
 	int session_active;
-- 
2.7.4