output: add wlr_output_set_layers()

include/wlr/types/wlr_output.h

@@ -434,6 +434,16 @@ uint32_t wlr_output_preferred_read_format(struct wlr_output *output);
  */
 void wlr_output_set_damage(struct wlr_output *output,
 	const pixman_region32_t *damage);
+/**
+ * Set the output layers state.
+ *
+ * See struct wlr_output_layer for more details on output layers.
+ *
+ * This state is double-buffered, see wlr_output_commit(). The layers array
+ * must remain valid until the wlr_output_test() or wlr_output_commit() call.
+ */
+void wlr_output_set_layers(struct wlr_output *output,
+	struct wlr_output_layer_state *layers, size_t layers_len);
 /**
  * Test whether the pending output state would be accepted by the backend. If
  * this function returns true, wlr_output_commit() can only fail due to a

include/wlr/types/wlr_output_layer.h

@@ -21,7 +21,8 @@
  *
  * To configure output layers, callers should call wlr_output_layer_create() to
  * create layers, attach struct wlr_output_layer_state onto
- * struct wlr_output_state to describe their new state, and commit the output.
+ * struct wlr_output_state via wlr_output_set_layers() to describe their new
+ * state, and commit the output via wlr_output_commit().
  *
  * Backends may have arbitrary limitations when it comes to displaying output
  * layers. Backends indicate whether or not a layer can be displayed via

types/output/output.c

@@ -486,6 +486,13 @@ void wlr_output_set_damage(struct wlr_output *output,
 	output->pending.committed |= WLR_OUTPUT_STATE_DAMAGE;
 }
 
+void wlr_output_set_layers(struct wlr_output *output,
+		struct wlr_output_layer_state *layers, size_t layers_len) {
+	output->pending.committed |= WLR_OUTPUT_STATE_LAYERS;
+	output->pending.layers = layers;
+	output->pending.layers_len = layers_len;
+}
+
 static void output_state_clear_gamma_lut(struct wlr_output_state *state) {
 	free(state->gamma_lut);
 	state->gamma_lut = NULL;