Improve dragging scene into 3D viewport

* When there's nothing to collide with:
    * Place the new scene on XZ plane when possible.
    * When the camera does not point toward the XZ plane or the
      intersection is too far away, place the new scene on a plane that
      is in front of the camera and parallel to the frame.
* Fixes positioning when in orthogonal view.
    * Place on physical collision point or the XZ plane when possible.
    * Otherwise, place it on the plane in front of the camera as if the
      camera was perspective.
* Makes use of snap settings when placing the new scene.

1 files changed, 28 insertions, 7 deletions

diff --git a/editor/plugins/node_3d_editor_plugin.cpp b/editor/plugins/node_3d_editor_plugin.cpp
index 3c9d93f13a..f29d546df0 100644
--- a/editor/plugins/node_3d_editor_plugin.cpp
+++ b/editor/plugins/node_3d_editor_plugin.cpp
@@ -2664,7 +2664,7 @@ void Node3DEditorViewport::_notification(int p_what) {
 				return;
 			}
 			if (preview_node->is_inside_tree()) {
-				preview_node_pos = _get_instance_position(preview_node_viewport_pos);
+				preview_node_pos = spatial_editor->snap_point(_get_instance_position(preview_node_viewport_pos));
 				Transform3D preview_gl_transform = Transform3D(Basis(), preview_node_pos);
 				preview_node->set_global_transform(preview_gl_transform);
 				if (!preview_node->is_visible()) {
@@ -3748,24 +3748,45 @@ void Node3DEditorViewport::assign_pending_data_pointers(Node3D *p_preview_node,
 
 Vector3 Node3DEditorViewport::_get_instance_position(const Point2 &p_pos) const {
 	const float MAX_DISTANCE = 50.0;
+	const float FALLBACK_DISTANCE = 5.0;
 
 	Vector3 world_ray = _get_ray(p_pos);
 	Vector3 world_pos = _get_ray_pos(p_pos);
 
-	Vector3 point = world_pos + world_ray * MAX_DISTANCE;
-
 	PhysicsDirectSpaceState3D *ss = get_tree()->get_root()->get_world_3d()->get_direct_space_state();
 
 	PhysicsDirectSpaceState3D::RayParameters ray_params;
 	ray_params.from = world_pos;
-	ray_params.to = world_pos + world_ray * MAX_DISTANCE;
+	ray_params.to = world_pos + world_ray * camera->get_far();
 
 	PhysicsDirectSpaceState3D::RayResult result;
 	if (ss->intersect_ray(ray_params, result)) {
-		point = result.position;
+		return result.position;
+	}
+
+	const bool is_orthogonal = camera->get_projection() == Camera3D::PROJECTION_ORTHOGONAL;
+
+	// The XZ plane.
+	Vector3 intersection;
+	Plane plane(Vector3(0, 1, 0));
+	if (plane.intersects_ray(world_pos, world_ray, &intersection)) {
+		if (is_orthogonal || world_pos.distance_to(intersection) <= MAX_DISTANCE) {
+			return intersection;
+		}
+	}
+
+	// Plane facing the camera using fallback distance.
+	if (is_orthogonal) {
+		plane = Plane(world_ray, cursor.pos - world_ray * (cursor.distance - FALLBACK_DISTANCE));
+	} else {
+		plane = Plane(world_ray, world_pos + world_ray * FALLBACK_DISTANCE);
+	}
+	if (plane.intersects_ray(world_pos, world_ray, &intersection)) {
+		return intersection;
 	}
 
-	return point;
+	// Not likely, but just in case...
+	return world_pos + world_ray * FALLBACK_DISTANCE;
 }
 
 AABB Node3DEditorViewport::_calculate_spatial_bounds(const Node3D *p_parent, bool p_exclude_top_level_transform) {
@@ -4045,7 +4066,7 @@ bool Node3DEditorViewport::_create_instance(Node *parent, String &path, const Po
 			gl_transform = parent_node3d->get_global_gizmo_transform();
 		}
 
-		gl_transform.origin = spatial_editor->snap_point(preview_node_pos);
+		gl_transform.origin = preview_node_pos;
 		gl_transform.basis *= node3d->get_transform().basis;
 
 		editor_data->get_undo_redo()->add_do_method(instantiated_scene, "set_global_transform", gl_transform);