compositor: add wlr_surface_state_has_buffer()

include/wlr/types/wlr_compositor.h

@@ -283,6 +283,19 @@ void wlr_surface_unmap(struct wlr_surface *surface);
  */
 bool wlr_surface_has_buffer(struct wlr_surface *surface);
 
+/**
+ * Check whether this surface state has an attached buffer.
+ *
+ * A surface has an attached buffer when the client commits with a non-null
+ * buffer. A surface will not have a buffer if the client never committed one,
+ * or committed a null buffer.
+ *
+ * Note that wlr_surface_state.buffer may be NULL even if this function returns
+ * true: the buffer field is reset after commit, to allow the buffer to be
+ * released to the client. Additionally, the buffer import or upload may fail.
+ */
+bool wlr_surface_state_has_buffer(const struct wlr_surface_state *state);
+
 /**
  * Get the texture of the buffer currently attached to this surface. Returns
  * NULL if no buffer is currently attached or if something went wrong with

types/wlr_compositor.c

@@ -720,7 +720,11 @@ struct wlr_texture *wlr_surface_get_texture(struct wlr_surface *surface) {
 }
 
 bool wlr_surface_has_buffer(struct wlr_surface *surface) {
-	return surface->current.buffer_width > 0 && surface->current.buffer_height > 0;
+	return wlr_surface_state_has_buffer(&surface->current);
+}
+
+bool wlr_surface_state_has_buffer(const struct wlr_surface_state *state) {
+	return state->buffer_width > 0 && state->buffer_height > 0;
 }
 
 void wlr_surface_map(struct wlr_surface *surface) {