From f9becb31e14e9ede8dc4c077d2ee76d450680357 Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Fri, 16 Feb 2024 13:40:39 +0100
Subject: [PATCH] scene: add wlr_scene_node_snapshot()

---
 include/wlr/types/wlr_scene.h |  9 ++++
 types/scene/wlr_scene.c       | 80 +++++++++++++++++++++++++++++++++++
 2 files changed, 89 insertions(+)

diff --git a/include/wlr/types/wlr_scene.h b/include/wlr/types/wlr_scene.h
index 253de1695..c742b2096 100644
--- a/include/wlr/types/wlr_scene.h
+++ b/include/wlr/types/wlr_scene.h
@@ -301,6 +301,15 @@ void wlr_scene_node_for_each_buffer(struct wlr_scene_node *node,
  */
 struct wlr_scene_node *wlr_scene_node_at(struct wlr_scene_node *node,
 	double lx, double ly, double *nx, double *ny);
+/**
+ * Create a new scene node which represents a snapshot of another node.
+ *
+ * The snapshot displays the same contents as the source node at the time of
+ * its creation. The snapshot is completely independent from the source node:
+ * when the source node is updated, the snapshot will stay as-is.
+ */
+struct wlr_scene_node *wlr_scene_node_snapshot(struct wlr_scene_node *node,
+	struct wlr_scene_tree *parent);
 
 /**
  * Create a new scene-graph.
diff --git a/types/scene/wlr_scene.c b/types/scene/wlr_scene.c
index 7e5b31363..aa993fd29 100644
--- a/types/scene/wlr_scene.c
+++ b/types/scene/wlr_scene.c
@@ -2008,3 +2008,83 @@ void wlr_scene_output_for_each_buffer(struct wlr_scene_output *scene_output,
 	scene_output_for_each_scene_buffer(&box, &scene_output->scene->tree.node, 0, 0,
 		iterator, user_data);
 }
+
+static bool scene_node_snapshot(struct wlr_scene_node *node, int lx, int ly,
+		struct wlr_scene_tree *snapshot_tree) {
+	if (!node->enabled) {
+		return true;
+	}
+
+	lx += node->x;
+	ly += node->y;
+
+	struct wlr_scene_node *snapshot_node = NULL;
+	switch (node->type) {
+	case WLR_SCENE_NODE_TREE:;
+		struct wlr_scene_tree *scene_tree = wlr_scene_tree_from_node(node);
+
+		struct wlr_scene_node *child;
+		wl_list_for_each(child, &scene_tree->children, link) {
+			scene_node_snapshot(node, lx, ly, snapshot_tree);
+		}
+		break;
+	case WLR_SCENE_NODE_RECT:;
+		struct wlr_scene_rect *scene_rect = wlr_scene_rect_from_node(node);
+
+		struct wlr_scene_rect *snapshot_rect = wlr_scene_rect_create(snapshot_tree,
+			scene_rect->width, scene_rect->height, scene_rect->color);
+		if (snapshot_rect == NULL) {
+			return false;
+		}
+		snapshot_node = &snapshot_rect->node;
+		break;
+	case WLR_SCENE_NODE_BUFFER:;
+		struct wlr_scene_buffer *scene_buffer = wlr_scene_buffer_from_node(node);
+
+		struct wlr_scene_buffer *snapshot_buffer = wlr_scene_buffer_create(snapshot_tree, NULL);
+		if (snapshot_buffer == NULL) {
+			return false;
+		}
+		snapshot_node = &snapshot_buffer->node;
+
+		wlr_scene_buffer_set_dest_size(snapshot_buffer, scene_buffer->dst_width, scene_buffer->dst_height);
+		wlr_scene_buffer_set_opaque_region(snapshot_buffer, &scene_buffer->opaque_region);
+		wlr_scene_buffer_set_source_box(snapshot_buffer, &scene_buffer->src_box);
+		wlr_scene_buffer_set_transform(snapshot_buffer, scene_buffer->transform);
+
+		struct wlr_scene_surface *scene_surface = wlr_scene_surface_try_from_buffer(scene_buffer);
+		if (scene_surface != NULL && scene_surface->surface->buffer != NULL) {
+			wlr_scene_buffer_set_buffer(snapshot_buffer, &scene_surface->surface->buffer->base);
+		} else {
+			wlr_scene_buffer_set_buffer(snapshot_buffer, scene_buffer->buffer);
+		}
+		break;
+	}
+
+	if (snapshot_node != NULL) {
+		wlr_scene_node_set_position(snapshot_node, lx, ly);
+	}
+
+	return true;
+}
+
+struct wlr_scene_node *wlr_scene_node_snapshot(struct wlr_scene_node *node,
+		struct wlr_scene_tree *parent) {
+	struct wlr_scene_tree *snapshot = wlr_scene_tree_create(parent);
+	if (snapshot == NULL) {
+		return NULL;
+	}
+
+	// Disable and enable the snapshot tree like so to atomically update
+	// the scene-graph. This will prevent over-damaging or other weirdness.
+	wlr_scene_node_set_enabled(&snapshot->node, false);
+
+	if (!scene_node_snapshot(node, 0, 0, snapshot)) {
+		wlr_scene_node_destroy(&snapshot->node);
+		return NULL;
+	}
+
+	wlr_scene_node_set_enabled(&snapshot->node, true);
+
+	return &snapshot->node;
+}