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);

tinywl/tinywl.c

@@ -449,8 +449,7 @@ static void process_cursor_motion(struct tinywl_server *server, uint32_t time) {
 		/* If there's no view under the cursor, set the cursor image to a
 		 * default. This is what makes the cursor image appear when you move it
 		 * around the screen, not over any views. */
-		wlr_xcursor_manager_set_cursor_image(
-				server->cursor_mgr, "default", server->cursor);
+		wlr_cursor_set_xcursor(server->cursor, server->cursor_mgr, "default");
 	}
 	if (surface) {
 		/*
@@ -927,9 +926,8 @@ int main(int argc, char *argv[]) {
 	/* Creates an xcursor manager, another wlroots utility which loads up
 	 * Xcursor themes to source cursor images from and makes sure that cursor
 	 * images are available at all scale factors on the screen (necessary for
-	 * HiDPI support). We add a cursor theme at scale factor 1 to begin with. */
+	 * HiDPI support). */
 	server.cursor_mgr = wlr_xcursor_manager_create(NULL, 24);
-	wlr_xcursor_manager_load(server.cursor_mgr, 1);
 
 	/*
 	 * wlr_cursor *only* displays an image on screen. It does not move around

types/wlr_cursor.c

@@ -11,6 +11,7 @@
 #include <wlr/types/wlr_compositor.h>
 #include <wlr/types/wlr_tablet_tool.h>
 #include <wlr/types/wlr_touch.h>
+#include <wlr/types/wlr_xcursor_manager.h>
 #include <wlr/util/box.h>
 #include <wlr/util/log.h>
 #include "types/wlr_output.h"
@@ -65,6 +66,9 @@ struct wlr_cursor_output_cursor {
 	struct wl_listener surface_commit;
 	struct wl_listener surface_destroy;
 	struct wl_listener output_commit;
+
+	// only when using an XCursor as the cursor image
+	struct wlr_xcursor *xcursor;
 };
 
 struct wlr_cursor_state {
@@ -380,6 +384,8 @@ static void cursor_output_cursor_reset_image(
 	wl_list_init(&output_cursor->surface_commit.link);
 	wl_list_init(&output_cursor->output_commit.link);
 	output_cursor->surface = NULL;
+
+	output_cursor->xcursor = NULL;
 }
 
 static void output_cursor_output_commit_surface(
@@ -419,6 +425,27 @@ void wlr_cursor_set_image(struct wlr_cursor *cur, const uint8_t *pixels,
 	}
 }
 
+void wlr_cursor_set_xcursor(struct wlr_cursor *cur,
+		struct wlr_xcursor_manager *manager, const char *name) {
+	struct wlr_cursor_output_cursor *output_cursor;
+	wl_list_for_each(output_cursor, &cur->state->output_cursors, link) {
+		float scale = output_cursor->output_cursor->output->scale;
+		wlr_xcursor_manager_load(manager, scale);
+		struct wlr_xcursor *xcursor = wlr_xcursor_manager_get_xcursor(manager, name, scale);
+		if (xcursor == NULL || output_cursor->xcursor == xcursor) {
+			continue;
+		}
+
+		cursor_output_cursor_reset_image(output_cursor);
+		output_cursor->xcursor = xcursor;
+
+		struct wlr_xcursor_image *image = xcursor->images[0];
+		wlr_output_cursor_set_image(output_cursor->output_cursor,
+			image->buffer, 4 * image->width, image->width, image->height,
+			image->hotspot_x, image->hotspot_y);
+	}
+}
+
 static void output_cursor_output_handle_surface_destroy(
 		struct wl_listener *listener, void *data) {
 	struct wlr_cursor_output_cursor *output_cursor =