Nodes are the base bricks with which Godot games are developed. They can be set as children of other nodes, resulting in a tree arrangement. A given node can contain any number of nodes as children (but there is only one scene tree root node) with the requirement that all siblings (direct children of a node) should have unique names.
Any tree of nodes is called a [i]scene[/i]. Scenes can be saved to the disk and then instanced into other scenes. This allows for very high flexibility in the architecture and data model of the projects. Nodes can optionally be added to groups. This makes it easy to reach a number of nodes from the code (for example an "enemies" group) to perform grouped actions.
[b]Scene tree:[/b] The [SceneTree] contains the active tree of nodes. When a node is added to the scene tree, it receives the NOTIFICATION_ENTER_TREE notification and its [method _enter_tree] callback is triggered. Children nodes are always added [i]after[/i] their parent node, i.e. the [method _enter_tree] callback of a parent node will be triggered before its child's.
Once all nodes have been added in the scene tree, they receive the NOTIFICATION_READY notification and their respective [method _ready] callbacks are triggered. For groups of nodes, the [method _ready] callback is called in reverse order, from the children up to the parent nodes.
It means that when adding a scene to the scene tree, the following order will be used for the callbacks: [method _enter_tree] of the parent, [method _enter_tree] of the children, [method _ready] of the children and finally [method _ready] of the parent (and that recursively for the whole scene).
[b]Processing:[/b] Nodes can be set to the "process" state, so that they receive a callback on each frame requesting them to process (do something). Normal processing (callback [method _process], toggled with [method set_process]) happens as fast as possible and is dependent on the frame rate, so the processing time [i]delta[/i] is variable. Physics processing (callback [method _physics_process], toggled with [method set_physics_process]) happens a fixed amount of times per second (by default 60) and is useful to link itself to the physics.
Nodes can also process input events. When set, the [method _input] function will be called for each input that the program receives. In many cases, this can be overkill (unless used for simple projects), and the [method _unhandled_input] function might be preferred; it is called when the input event was not handled by anyone else (typically, GUI [Control] nodes), ensuring that the node only receives the events that were meant for it.
To keep track of the scene hierarchy (especially when instancing scenes into other scenes), an "owner" can be set for the node with [method set_owner]. This keeps track of who instanced what. This is mostly useful when writing editors and tools, though.
Finally, when a node is freed with [method free] or [method queue_free], it will also free all its children.
[b]Networking with nodes:[/b] After connecting to a server (or making one, see [NetworkedMultiplayerENet]) it is possible to use the built-in RPC (remote procedure call) system to easily communicate over the network. By calling [method rpc] with a method name, it will be called locally, and in all connected peers (peers = clients and the server that accepts connections), with behaviour varying depending on the network mode ([method set_network_mode]) on the receiving peer. To identify which [code]Node[/code] receives the RPC call Godot will use its [NodePath] (make sure node names are the same on all peers).
Called when the node enters the [SceneTree] (e.g. upon instancing, scene changing or after calling [method add_child] in a script). If the node has children, its [method _enter_tree] callback will be called first, and then that of the children.
Corresponds to the NOTIFICATION_ENTER_TREE notification in [method Object._notification].
</description>
</method>
<methodname="_exit_tree"qualifiers="virtual">
<returntype="void">
</return>
<description>
Called when the node leaves the [SceneTree] (e.g. upon freeing, scene changing or after calling [method remove_child] in a script). If the node has children, its [method _exit_tree] callback will be called last, after all its children have left the tree.
Corresponds to the NOTIFICATION_EXIT_TREE notification in [method Object._notification].
It is only called if input processing is enabled, which is done automatically if this method is overriden, and can be toggled with [method set_process_input].
Called during the physics processing step of the main loop. Physics processing means that the frame rate is synced to the physics, i.e. the [code]delta[/code] variable should be constant.
It is only called if physics processing is enabled, which is done automatically if this method is overriden, and can be toggled with [method set_physics_process].
Called during the processing step of the main loop. Processing happens at every frame and as fast as possible, so the [code]delta[/code] time since the previous frame is not constant.
Corresponds to the NOTIFICATION_PROCESS notification in [method Object._notification].
</description>
</method>
<methodname="_ready"qualifiers="virtual">
<returntype="void">
</return>
<description>
Called when the node is "ready", i.e. when both the node and its children have entered the scene tree. If the node has children, their [method _ready] callback gets triggered first, and the node will receive the ready notification only afterwards.
Corresponds to the NOTIFICATION_READY notification in [method Object._notification].
It is only called if unhandled input processing is enabled, which is done automatically if this method is overriden, and can be toggled with [method set_process_unhandled_input].
Add a child [code]Node[/code]. Nodes can have as many children as they want, but every child must have a unique name. Children nodes are automatically deleted when the parent node is deleted, so deleting a whole scene is performed by deleting its topmost node.
The optional boolean argument enforces creating child nodes with human-readable names, based on the name of the node being instanced instead of its type only.
Add a node to a group. Groups are helpers to name and organize a subset of nodes, like for example "enemies" or "collectables". A [code]Node[/code] can be in any number of groups. Nodes can be assigned a group at any time, but will not be added to it until they are inside the scene tree (see [method is_inside_tree]).
Return true if the node can process, i.e. whether its pause mode allows processing while the scene tree is paused (see [method set_pause_mode]). Always returns true if the scene tree is not paused, and false if the node is not in the tree. FIXME: Why FAIL_COND?
Finds a descendant of this node whose name matches [code]mask[/code] as in [method String.match] (i.e. case sensitive, but '*' matches zero or more characters and '?' matches any single character except '.'). Note that it does not match against the full path, just against individual node names.
Returns a filename that may be contained by the node. When a scene is instanced from a file, it topmost node contains the filename from where it was loaded (see [method set_filename]).
Fetches a node. The [NodePath] must be valid (or else an error will be raised) and can be either the path to child node, a relative path (from the current node to another node), or an absolute path to a node.
Returns the relative path from the current node to the specified node in "node" argument. Both nodes must be in the same scene, or else the function will fail.
Returns the time elapsed since the last physics-bound frame (see [method _physics_process]). This is always a constant value in physics processing unless the frames per second is changed in [OS].
Moves a child node to a different position (order) amongst the other children. Since calls, signals, etc are performed by tree order, changing the order of children nodes may be useful.
Calls the method (if present) with the arguments given in "args" on this Node and recursively on all children. If the parent_first argument is true then the method will be called on the current [code]Node[/code] first, then on all children. If it is false then the children will get called first.
Notify the current node and all its children recursively by calling notification() in all of them.
</description>
</method>
<methodname="queue_free">
<returntype="void">
</return>
<description>
Queues a node for deletion at the end of the current frame. When deleted, all of its children nodes will be deleted as well. This method ensures it's safe to delete the node, contrary to [method Object.free]. Use [method Object.is_queued_for_deletion] to know whether a node will be deleted at the end of the frame.
Moves this node to the top of the array of nodes of the parent node. This is often useful on GUIs ([Control]), because their order of drawing fully depends on their order in the tree.
Removes a node and set all its children as children of the parent node (if exists). All even subscriptions that pass by the removed node will be unsubscribed.
Sends a remote procedure call request to all peers on the network (and locally), optionally sending additional data as arguments. Call request will be received by nodes with the same [NodePath].
A node can contain a filename. This filename should not be changed by the user, unless writing editors and tools. When a scene is instanced from a file, it topmost node contains the filename from where it was loaded.
Sets the name of the [code]Node[/code]. Name must be unique within parent, and setting an already existing name will cause for the node to be automatically renamed.
Sets the node network master to the peer with the given peer ID. The network master is the peer that has authority over it on the network. Inherited from the parent node by default, which ultimately defaults to peer ID 1 (the server).
Sets the node owner. A node can have any other node as owner (as long as a valid parent, grandparent, etc ascending in the tree). When saving a node (using SceneSaver) all the nodes it owns will be saved with it. This allows to create complex SceneTrees, with instancing and subinstancing.
Enables or disables the node's physics (alias fixed framerate) processing. When a node is being processed, it will receive a NOTIFICATION_PHYSICS_PROCESS at a fixed (usually 60 fps, check [OS] to change that) interval (and the [method _physics_process] callback will be called if exists). Enabled automatically if [method _physics_process] is overriden. Any calls to this before [method _ready] will be ignored.
Enables or disables node processing. When a node is being processed, it will receive a NOTIFICATION_PROCESS on every drawn frame (and the [method _process] callback will be called if exists). Enabled automatically if [method _process] is overriden. Any calls to this before [method _ready] will be ignored.
Enables input processing for node. This is not required for GUI controls! It hooks up the node to receive all input (see [method _input]). Enabled automatically if [method _input] is overriden. Any calls to this before [method _ready] will be ignored.
Enables unhandled input processing for node. This is not required for GUI controls! It hooks up the node to receive all input that was not previously handled before (usually by a [Control]). Enabled automatically if [method _unhandled_input] is overriden. Any calls to this before [method _ready] will be ignored.
Enables unhandled key input processing for node. Enabled automatically if [method _unhandled_key_input] is overriden. Any calls to this before [method _ready] will be ignored.
