compositor: add wlr_surface_set_preferred_buffer_transform()

References: https://gitlab.freedesktop.org/wayland/wayland/-/merge_requests/220

include/wlr/types/wlr_compositor.h

@@ -165,6 +165,8 @@ struct wlr_surface {
 	bool opaque;
 
 	int32_t preferred_buffer_scale;
+	bool preferred_buffer_transform_sent;
+	enum wl_output_transform preferred_buffer_transform;
 };
 
 struct wlr_renderer;
@@ -330,6 +332,15 @@ void wlr_surface_unlock_cached(struct wlr_surface *surface, uint32_t seq);
 void wlr_surface_set_preferred_buffer_scale(struct wlr_surface *surface,
 	int32_t scale);
 
+/**
+ * Set the preferred buffer transform for the surface.
+ *
+ * This sends an event to the client indicating the preferred transform to use
+ * for buffers attached to this surface.
+ */
+void wlr_surface_set_preferred_buffer_transform(struct wlr_surface *surface,
+	enum wl_output_transform transform);
+
 /**
  * Create the wl_compositor global, which can be used by clients to create
  * surfaces and regions.

types/wlr_compositor.c

@@ -1106,6 +1106,23 @@ void wlr_surface_set_preferred_buffer_scale(struct wlr_surface *surface,
 	surface->preferred_buffer_scale = scale;
 }
 
+void wlr_surface_set_preferred_buffer_transform(struct wlr_surface *surface,
+		enum wl_output_transform transform) {
+	if (wl_resource_get_version(surface->resource) <
+			WL_SURFACE_PREFERRED_BUFFER_TRANSFORM_SINCE_VERSION) {
+		return;
+	}
+
+	if (surface->preferred_buffer_transform == transform &&
+			surface->preferred_buffer_transform_sent) {
+		return;
+	}
+
+	wl_surface_send_preferred_buffer_transform(surface->resource, transform);
+	surface->preferred_buffer_transform_sent = true;
+	surface->preferred_buffer_transform = transform;
+}
+
 static const struct wl_compositor_interface compositor_impl;
 
 static struct wlr_compositor *compositor_from_resource(