Nodes are Godot's building blocks. They can be assigned as the child of another node, resulting in a tree arrangement. A given node can contain any number of nodes as children with the requirement that all siblings (direct children of a node) should have unique names.
A 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 Godot projects. Nodes can also optionally be added to groups. This makes it possible to access a number of nodes from code (an "enemies" group, for example) 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. Child 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, starting with the children and moving up to the parent nodes.
This means that when adding a node 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 (recursively for the entire scene tree).
[b]Processing:[/b] Nodes can override 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 passed as an argument. Physics processing (callback [method _physics_process], toggled with [method set_physics_process]) happens a fixed number of times per second (60 by default) and is useful for code related to the physics engine.
Nodes can also process input events. When present, 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 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]) of the receiving peer. To identify which node 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.
Called when the node is about to leave 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] and signal [signal tree_exiting]. To get notified when the node has already left the active tree, connect to the [signal tree_exited]
It is only called if input processing is enabled, which is done automatically if this method is overridden, 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 overridden, 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.
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] callbacks get triggered first, and the parent node will receive the ready notification afterwards.
It is only called if unhandled input processing is enabled, which is done automatically if this method is overridden, and can be toggled with [method set_process_unhandled_input].
Adds a child node. Nodes can have any number of children, but every child must have a unique name. Child nodes are automatically deleted when the parent node is deleted, so an entire scene can be removed by deleting its topmost node.
Setting "legible_unique_name" [code]true[/code] creates child nodes with human-readable names, based on the name of the node being instanced instead of its type.
Adds a child node. The child is placed below the given node in the list of children.
Setting "legible_unique_name" [code]true[/code] creates child nodes with human-readable names, based on the name of the node being instanced instead of its type.
Adds the node to a group. Groups are helpers to name and organize a subset of nodes, for example "enemies" or "collectables". A node can be in any number of groups. Nodes can be assigned a group at any time, but will not be added until they are inside the scene tree (see [method is_inside_tree]).
Returns [code]true[/code] if the node can process while the scene tree is paused (see [method set_pause_mode]). Always returns [code]true[/code] if the scene tree is not paused, and [code]false[/code] 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.
Fetches a node. The [NodePath] can be either a relative path (from the current node) or an absolute path (in the scene tree) to a node. If the path does not exist, a [code]null instance[/code] is returned and attempts to access it will result in an "Attempt to call <method> on a null instance." error.
Returns the relative path from the current node to the specified node in "node" argument. Both nodes must be in the same scene, or 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 given method (if present) with the arguments given in [code]args[/code] on this node and recursively on all its children. If the parent_first argument is [code]true[/code] then the method will be called on the current node first, then on all children. If it is [code]false[/code] then the children will be called first.
Queues a node for deletion at the end of the current frame. When deleted, all of its child 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 check 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 in GUIs ([Control] nodes), because their order of drawing depends on their order in the tree.
Removes a node and sets all its children as children of the parent node (if it exists). All event 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].
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).
Enables or disables physics (i.e. fixed framerate) processing. When a node is being processed, it will receive a NOTIFICATION_PHYSICS_PROCESS at a fixed (usually 60 fps, see [OS] to change) interval (and the [method _physics_process] callback will be called if exists). Enabled automatically if [method _physics_process] is overridden. Any calls to this before [method _ready] will be ignored.
Enables or disables 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 overridden. Any calls to this before [method _ready] will be ignored.
Enables or disables input processing. This is not required for GUI controls! Enabled automatically if [method _input] is overridden. Any calls to this before [method _ready] will be ignored.
Enables unhandled input processing. This is not required for GUI controls! It enables the node to receive all input that was not previously handled (usually by a [Control]). Enabled automatically if [method _unhandled_input] is overridden. Any calls to this before [method _ready] will be ignored.
Enables unhandled key input processing. Enabled automatically if [method _unhandled_key_input] is overridden. Any calls to this before [method _ready] will be ignored.
The node owner. A node can have any other node as owner (as long as it is 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 for the creation of complex [SceneTree]s, with instancing and subinstancing.
