output: atomic mode, enabled, scale and transform

This commit makes more output properties (mode, enabled, scale and transform)
atomic. This means that they are double-buffered and only applied on commit.

Compositors now need to call wlr_output_commit after setting any of those
properties.

Internally, backends still apply properties sequentially. The behaviour should
be exactly the same as before. Future commits will update some backends to take
advantage of the atomic interface. Some backends are non-atomic by design, e.g.
the X11 backend or the legacy DRM backend.

Updates: https://github.com/swaywm/wlroots/issues/1640

2 files changed, 42 insertions, 10 deletions

diff --git a/include/wlr/interfaces/wlr_output.h b/include/wlr/interfaces/wlr_output.h
index a9a89c34..8d4a3fd8 100644
--- a/include/wlr/interfaces/wlr_output.h
+++ b/include/wlr/interfaces/wlr_output.h
@@ -15,10 +15,6 @@
 #include <wlr/types/wlr_output.h>
 
 struct wlr_output_impl {
-	bool (*enable)(struct wlr_output *output, bool enable);
-	bool (*set_mode)(struct wlr_output *output, struct wlr_output_mode *mode);
-	bool (*set_custom_mode)(struct wlr_output *output, int32_t width,
-		int32_t height, int32_t refresh);
 	bool (*set_cursor)(struct wlr_output *output, struct wlr_texture *texture,
 		int32_t scale, enum wl_output_transform transform,
 		int32_t hotspot_x, int32_t hotspot_y, bool update_texture);
diff --git a/include/wlr/types/wlr_output.h b/include/wlr/types/wlr_output.h
index 281f7daf..be04ec3b 100644
--- a/include/wlr/types/wlr_output.h
+++ b/include/wlr/types/wlr_output.h
@@ -49,6 +49,10 @@ struct wlr_output_cursor {
 enum wlr_output_state_field {
 	WLR_OUTPUT_STATE_BUFFER = 1 << 0,
 	WLR_OUTPUT_STATE_DAMAGE = 1 << 1,
+	WLR_OUTPUT_STATE_MODE = 1 << 2,
+	WLR_OUTPUT_STATE_ENABLED = 1 << 3,
+	WLR_OUTPUT_STATE_SCALE = 1 << 4,
+	WLR_OUTPUT_STATE_TRANSFORM = 1 << 5,
 };
 
 enum wlr_output_state_buffer_type {
@@ -56,16 +60,32 @@ enum wlr_output_state_buffer_type {
 	WLR_OUTPUT_STATE_BUFFER_SCANOUT,
 };
 
+enum wlr_output_state_mode_type {
+	WLR_OUTPUT_STATE_MODE_FIXED,
+	WLR_OUTPUT_STATE_MODE_CUSTOM,
+};
+
 /**
  * Holds the double-buffered output state.
  */
 struct wlr_output_state {
 	uint32_t committed; // enum wlr_output_state_field
 	pixman_region32_t damage; // output-buffer-local coordinates
+	bool enabled;
+	float scale;
+	enum wl_output_transform transform;
 
 	// only valid if WLR_OUTPUT_STATE_BUFFER
 	enum wlr_output_state_buffer_type buffer_type;
 	struct wlr_buffer *buffer; // if WLR_OUTPUT_STATE_BUFFER_SCANOUT
+
+	// only valid if WLR_OUTPUT_STATE_MODE
+	enum wlr_output_state_mode_type mode_type;
+	struct wlr_output_mode *mode;
+	struct {
+		int32_t width, height;
+		int32_t refresh; // mHz, may be zero
+	} custom_mode;
 };
 
 struct wlr_output_impl;
@@ -183,8 +203,11 @@ struct wlr_surface;
 /**
  * Enables or disables the output. A disabled output is turned off and doesn't
  * emit `frame` events.
+ *
+ * Whether an output is enabled is double-buffered state, see
+ * `wlr_output_commit`.
  */
-bool wlr_output_enable(struct wlr_output *output, bool enable);
+void wlr_output_enable(struct wlr_output *output, bool enable);
 void wlr_output_create_global(struct wlr_output *output);
 void wlr_output_destroy_global(struct wlr_output *output);
 /**
@@ -194,17 +217,31 @@ void wlr_output_destroy_global(struct wlr_output *output);
 struct wlr_output_mode *wlr_output_preferred_mode(struct wlr_output *output);
 /**
  * Sets the output mode. Enables the output if it's currently disabled.
+ *
+ * Mode is double-buffered state, see `wlr_output_commit`.
  */
-bool wlr_output_set_mode(struct wlr_output *output,
+void wlr_output_set_mode(struct wlr_output *output,
 	struct wlr_output_mode *mode);
 /**
  * Sets a custom mode on the output. If modes are available, they are preferred.
  * Setting `refresh` to zero lets the backend pick a preferred value.
+ *
+ * Custom mode is double-buffered state, see `wlr_output_commit`.
  */
-bool wlr_output_set_custom_mode(struct wlr_output *output, int32_t width,
+void wlr_output_set_custom_mode(struct wlr_output *output, int32_t width,
 	int32_t height, int32_t refresh);
+/**
+ * Sets a transform for the output.
+ *
+ * Transform is double-buffered state, see `wlr_output_commit`.
+ */
 void wlr_output_set_transform(struct wlr_output *output,
 	enum wl_output_transform transform);
+/**
+ * Sets a scale for the output.
+ *
+ * Scale is double-buffered state, see `wlr_output_commit`.
+ */
 void wlr_output_set_scale(struct wlr_output *output, float scale);
 void wlr_output_set_subpixel(struct wlr_output *output,
 	enum wl_output_subpixel subpixel);
@@ -262,9 +299,8 @@ void wlr_output_set_damage(struct wlr_output *output,
 	pixman_region32_t *damage);
 /**
  * Commit the pending output state. If `wlr_output_attach_render` has been
- * called, the pending frame will be submitted for display.
- *
- * This function schedules a `frame` event.
+ * called, the pending frame will be submitted for display and a `frame` event
+ * will be scheduled.
  */
 bool wlr_output_commit(struct wlr_output *output);
 /**