cursor: add wlr_cursor_set_xcursor()

This keeps track of the last set XCursor. If it hasn't changed,
skip the texture upload.

In the future, support for animated XCursors can be added.

Closes: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3436

include/wlr/types/wlr_cursor.h

@@ -14,6 +14,7 @@
 #include <wlr/types/wlr_output.h>
 
 struct wlr_input_device;
+struct wlr_xcursor_manager;
 
 /**
  * wlr_cursor implements the behavior of the "cursor", that is, the image on the
@@ -146,6 +147,14 @@ void wlr_cursor_set_image(struct wlr_cursor *cur, const uint8_t *pixels,
 	int32_t stride, uint32_t width, uint32_t height, int32_t hotspot_x,
 	int32_t hotspot_y, float scale);
 
+/**
+ * Set the cursor image from an XCursor theme.
+ *
+ * The image will be loaded from the struct wlr_xcursor_manager.
+ */
+void wlr_cursor_set_xcursor(struct wlr_cursor *cur,
+	struct wlr_xcursor_manager *manager, const char *name);
+
 /**
  * Set the cursor surface. The surface can be committed to update the cursor
  * image. The surface position is subtracted from the hotspot. A NULL surface

include/wlr/types/wlr_xcursor_manager.h

@@ -62,6 +62,8 @@ struct wlr_xcursor *wlr_xcursor_manager_get_xcursor(
  * scale factors. struct wlr_cursor will take over from this point and ensure
  * the correct cursor is used on each output, assuming a
  * struct wlr_output_layout is attached to it.
+ *
+ * Deprecated: wlr_cursor_set_xcursor() should be used instead.
  */
 void wlr_xcursor_manager_set_cursor_image(struct wlr_xcursor_manager *manager,
 	const char *name, struct wlr_cursor *cursor);