output: add backend docs

include/wlr/interfaces/wlr_output.h

@@ -14,31 +14,128 @@
 #include <wlr/types/wlr_box.h>
 #include <wlr/types/wlr_output.h>
 
+/**
+ * A backend implementation of wlr_output.
+ *
+ * The functions commit, attach_render and rollback_render are mandatory. Other
+ * functions are optional.
+ */
 struct wlr_output_impl {
+	/**
+	 * Set the output cursor plane image.
+	 *
+	 * The parameters describe the image texture, its scale and its transform.
+	 * If the scale and transform doesn't match the output's, the backend is
+	 * responsible for scaling and transforming the texture appropriately.
+	 * If texture is NULL, the cursor should be hidden.
+	 *
+	 * The hotspot indicates the offset that needs to be applied to the
+	 * top-left corner of the image to match the cursor position. In other
+	 * words, the image should be displayed at (x - hotspot_x, y - hotspot_y).
+	 *
+	 * If update_texture is true, all parameters need to be taken into account.
+	 * If update_texture is false, only the hotspot is to be updated.
+	 */
 	bool (*set_cursor)(struct wlr_output *output, struct wlr_texture *texture,
 		float scale, enum wl_output_transform transform,
 		int32_t hotspot_x, int32_t hotspot_y, bool update_texture);
+	/**
+	 * Set the output cursor plane position.
+	 *
+	 * The position is relative to the cursor hotspot, see set_cursor.
+	 */
 	bool (*move_cursor)(struct wlr_output *output, int x, int y);
+	/**
+	 * Cleanup backend-specific resources tied to the output.
+	 */
 	void (*destroy)(struct wlr_output *output);
+	/**
+	 * Make the output's back-buffer current for the renderer.
+	 *
+	 * buffer_age must be set to the buffer age in number of frames, or -1 if
+	 * unknown.
+	 */
 	bool (*attach_render)(struct wlr_output *output, int *buffer_age);
+	/**
+	 * Unset the current renderer's buffer.
+	 *
+	 * This is the opposite of attach_render.
+	 */
+	void (*rollback_render)(struct wlr_output *output);
+	/**
+	 * Check that the pending output state is a valid configuration.
+	 *
+	 * If this function returns true, commit can only fail due to a runtime
+	 * error.
+	 */
 	bool (*test)(struct wlr_output *output);
+	/**
+	 * Commit the pending output state.
+	 *
+	 * If a buffer has been attached, a frame event is scheduled.
+	 */
 	bool (*commit)(struct wlr_output *output);
-	void (*rollback_render)(struct wlr_output *output);
+	/**
+	 * Get the maximum number of gamma LUT elements for each channel.
+	 *
+	 * Zero can be returned if the output doesn't support gamma LUTs.
+	 */
 	size_t (*get_gamma_size)(struct wlr_output *output);
+	/**
+	 * Export the output's current back-buffer as a DMA-BUF.
+	 */
 	bool (*export_dmabuf)(struct wlr_output *output,
 		struct wlr_dmabuf_attributes *attribs);
 };
 
+/**
+ * Initialize a new output.
+ */
 void wlr_output_init(struct wlr_output *output, struct wlr_backend *backend,
 	const struct wlr_output_impl *impl, struct wl_display *display);
+/**
+ * Update the current output mode.
+ *
+ * The backend must call this function when the mode is updated to notify
+ * compositors about the change.
+ */
 void wlr_output_update_mode(struct wlr_output *output,
 	struct wlr_output_mode *mode);
+/**
+ * Update the current output custom mode.
+ *
+ * The backend must call this function when the mode is updated to notify
+ * compositors about the change.
+ */
 void wlr_output_update_custom_mode(struct wlr_output *output, int32_t width,
 	int32_t height, int32_t refresh);
+/**
+ * Update the current output status.
+ *
+ * The backend must call this function when the status is updated to notify
+ * compositors about the change.
+ */
 void wlr_output_update_enabled(struct wlr_output *output, bool enabled);
+/**
+ * Notify compositors that they need to submit a new frame in order to apply
+ * output changes.
+ */
 void wlr_output_update_needs_frame(struct wlr_output *output);
+/**
+ * Notify compositors that the output needs to be fully repainted.
+ */
 void wlr_output_damage_whole(struct wlr_output *output);
+/**
+ * Send a frame event.
+ *
+ * See wlr_output.events.frame.
+ */
 void wlr_output_send_frame(struct wlr_output *output);
+/**
+ * Send a present event.
+ *
+ * See wlr_output.events.present.
+ */
 void wlr_output_send_present(struct wlr_output *output,
 	struct wlr_output_event_present *event);