# node.rs - source
Source of the Rust file `maplibre/src/render/graph/node.rs`.
Keywords: rust, rustlang, rust-lang

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    use super::{
        Edge, InputSlotError, OutputSlotError, RenderGraphContext, RenderGraphError, RunSubGraphError,
        SlotInfo, SlotInfos,
    };
    use crate::render::RenderState;
    use downcast_rs::{impl_downcast, Downcast};
    use std::{borrow::Cow, fmt::Debug};
    use thiserror::Error;

    /// The context with all information required to interact with the GPU.
    ///
    /// The [`Device`] is used to create render resources and the
    /// the [`CommandEncoder`] is used to record a series of GPU operations.
    pub struct RenderContext<'d> {
        pub device: &'d wgpu::Device,
        pub command_encoder: wgpu::CommandEncoder,
    }

    /// A [`Node`] identifier.
    /// It automatically generates its own random uuid.
    ///
    /// This id is used to reference the node internally (edges, etc).
    #[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
    pub struct NodeId(usize);

    impl NodeId {
        #[allow(clippy::new_without_default)]
        pub fn new(id: usize) -> Self {
            NodeId(id)
        }
    }

    /// A render node that can be added to a [`RenderGraph`](super::RenderGraph).
    ///
    /// Nodes are the fundamental part of the graph and used to extend its functionality, by
    /// generating draw calls and/or running subgraphs.
    /// They are added via the `render_graph::add_node(my_node)` method.
    ///
    /// To determine their position in the graph and ensure that all required dependencies (inputs)
    /// are already executed, [`Edges`](Edge) are used.
    ///
    /// A node can produce outputs used as dependencies by other nodes.
    /// Those inputs and outputs are called slots and are the default way of passing render data
    /// inside the graph. For more information see [`SlotType`](super::SlotType).
    pub trait Node: Downcast + Send + Sync + 'static {
        /// Specifies the required input slots for this node.
        /// They will then be available during the run method inside the [`RenderGraphContext`].
        fn input(&self) -> Vec<SlotInfo> {
            Vec::new()
        }

        /// Specifies the produced output slots for this node.
        /// They can then be passed one inside [`RenderGraphContext`] during the run method.
        fn output(&self) -> Vec<SlotInfo> {
            Vec::new()
        }

        /// Updates internal node state using the current [`RenderState`] prior to the run method.
        fn update(&mut self, _state: &mut RenderState) {}

        /// Runs the graph node logic, issues draw calls, updates the output slots and
        /// optionally queues up subgraphs for execution. The graph data, input and output values are
        /// passed via the [`RenderGraphContext`].
        fn run(
            &self,
            graph: &mut RenderGraphContext,
            render_context: &mut RenderContext,
            state: &RenderState,
        ) -> Result<(), NodeRunError>;
    }

    impl_downcast!(Node);

    #[derive(Error, Debug, Eq, PartialEq)]
    pub enum NodeRunError {
        #[error("encountered an input slot error")]
        InputSlotError(#[from] InputSlotError),
        #[error("encountered an output slot error")]
        OutputSlotError(#[from] OutputSlotError),
        #[error("encountered an error when running a sub-graph")]
        RunSubGraphError(#[from] RunSubGraphError),
    }

    /// A collection of input and output [`Edges`](Edge) for a [`Node`].
    #[derive(Debug)]
    pub struct Edges {
        id: NodeId,
        input_edges: Vec<Edge>,
        output_edges: Vec<Edge>,
    }

    impl Edges {
        /// Returns all "input edges" (edges going "in") for this node .
        #[inline]
        pub fn input_edges(&self) -> &[Edge] {
            &self.input_edges
        }

        /// Returns all "output edges" (edges going "out") for this node .
        #[inline]
        pub fn output_edges(&self) -> &[Edge] {
            &self.output_edges
        }

        /// Returns this node's id.
        #[inline]
        pub fn id(&self) -> NodeId {
            self.id
        }

        /// Adds an edge to the `input_edges` if it does not already exist.
        pub(crate) fn add_input_edge(&mut self, edge: Edge) -> Result<(), RenderGraphError> {
            if self.has_input_edge(&edge) {
                return Err(RenderGraphError::EdgeAlreadyExists(edge));
            }
            self.input_edges.push(edge);
            Ok(())
        }

        /// Removes an edge from the `input_edges` if it exists.
        pub(crate) fn remove_input_edge(&mut self, edge: Edge) -> Result<(), RenderGraphError> {
            if let Some((index, _)) = self
                .input_edges
                .iter()
                .enumerate()
                .find(|(_i, e)| **e == edge)
            {
                self.input_edges.swap_remove(index);
                Ok(())
            } else {
                Err(RenderGraphError::EdgeDoesNotExist(edge))
            }
        }

        /// Adds an edge to the `output_edges` if it does not already exist.
        pub(crate) fn add_output_edge(&mut self, edge: Edge) -> Result<(), RenderGraphError> {
            if self.has_output_edge(&edge) {
                return Err(RenderGraphError::EdgeAlreadyExists(edge));
            }
            self.output_edges.push(edge);
            Ok(())
        }

        /// Removes an edge from the `output_edges` if it exists.
        pub(crate) fn remove_output_edge(&mut self, edge: Edge) -> Result<(), RenderGraphError> {
            if let Some((index, _)) = self
                .output_edges
                .iter()
                .enumerate()
                .find(|(_i, e)| **e == edge)
            {
                self.output_edges.swap_remove(index);
                Ok(())
            } else {
                Err(RenderGraphError::EdgeDoesNotExist(edge))
            }
        }

        /// Checks whether the input edge already exists.
        pub fn has_input_edge(&self, edge: &Edge) -> bool {
            self.input_edges.contains(edge)
        }

        /// Checks whether the output edge already exists.
        pub fn has_output_edge(&self, edge: &Edge) -> bool {
            self.output_edges.contains(edge)
        }

        /// Searches the `input_edges` for a [`Edge::SlotEdge`],
        /// which `input_index` matches the `index`;
        pub fn get_input_slot_edge(&self, index: usize) -> Result<&Edge, RenderGraphError> {
            self.input_edges
                .iter()
                .find(|e| {
                    if let Edge::SlotEdge { input_index, .. } = e {
                        *input_index == index
                    } else {
                        false
                    }
                })
                .ok_or(RenderGraphError::UnconnectedNodeInputSlot {
                    input_slot: index,
                    node: self.id,
                })
        }

        /// Searches the `output_edges` for a [`Edge::SlotEdge`],
        /// which `output_index` matches the `index`;
        pub fn get_output_slot_edge(&self, index: usize) -> Result<&Edge, RenderGraphError> {
            self.output_edges
                .iter()
                .find(|e| {
                    if let Edge::SlotEdge { output_index, .. } = e {
                        *output_index == index
                    } else {
                        false
                    }
                })
                .ok_or(RenderGraphError::UnconnectedNodeOutputSlot {
                    output_slot: index,
                    node: self.id,
                })
        }
    }

    /// The internal representation of a [`Node`], with all data required
    /// by the [`RenderGraph`](super::RenderGraph).
    ///
    /// The `input_slots` and `output_slots` are provided by the `node`.
    pub struct NodeState {
        pub id: NodeId,
        pub name: Option<Cow<'static, str>>,
        /// The name of the type that implements [`Node`].
        pub type_name: &'static str,
        pub node: Box<dyn Node>,
        pub input_slots: SlotInfos,
        pub output_slots: SlotInfos,
        pub edges: Edges,
    }

    impl Debug for NodeState {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            writeln!(f, "{:?} ({:?})", self.id, self.name)
        }
    }

    impl NodeState {
        /// Creates an [`NodeState`] without edges, but the `input_slots` and `output_slots`
        /// are provided by the `node`.
        pub fn new<T>(id: NodeId, node: T) -> Self
        where
            T: Node,
        {
            NodeState {
                id,
                name: None,
                input_slots: node.input().into(),
                output_slots: node.output().into(),
                node: Box::new(node),
                type_name: std::any::type_name::<T>(),
                edges: Edges {
                    id,
                    input_edges: Vec::new(),
                    output_edges: Vec::new(),
                },
            }
        }

        /// Retrieves the [`Node`].
        pub fn node<T>(&self) -> Result<&T, RenderGraphError>
        where
            T: Node,
        {
            self.node
                .downcast_ref::<T>()
                .ok_or(RenderGraphError::WrongNodeType)
        }

        /// Retrieves the [`Node`] mutably.
        pub fn node_mut<T>(&mut self) -> Result<&mut T, RenderGraphError>
        where
            T: Node,
        {
            self.node
                .downcast_mut::<T>()
                .ok_or(RenderGraphError::WrongNodeType)
        }

        /// Validates that each input slot corresponds to an input edge.
        pub fn validate_input_slots(&self) -> Result<(), RenderGraphError> {
            for i in 0..self.input_slots.len() {
                self.edges.get_input_slot_edge(i)?;
            }

            Ok(())
        }

        /// Validates that each output slot corresponds to an output edge.
        pub fn validate_output_slots(&self) -> Result<(), RenderGraphError> {
            for i in 0..self.output_slots.len() {
                self.edges.get_output_slot_edge(i)?;
            }

            Ok(())
        }
    }

    /// A [`NodeLabel`] is used to reference a [`NodeState`] by either its name or [`NodeId`]
    /// inside the [`RenderGraph`](super::RenderGraph).
    #[derive(Debug, Clone, Eq, PartialEq)]
    pub enum NodeLabel {
        Id(NodeId),
        Name(Cow<'static, str>),
    }

    impl From<&NodeLabel> for NodeLabel {
        fn from(value: &NodeLabel) -> Self {
            value.clone()
        }
    }

    impl From<String> for NodeLabel {
        fn from(value: String) -> Self {
            NodeLabel::Name(value.into())
        }
    }

    impl From<&'static str> for NodeLabel {
        fn from(value: &'static str) -> Self {
            NodeLabel::Name(value.into())
        }
    }

    impl From<NodeId> for NodeLabel {
        fn from(value: NodeId) -> Self {
            NodeLabel::Id(value)
        }
    }

    /// A [`Node`] without any inputs, outputs and subgraphs, which does nothing when run.
    /// Used (as a label) to bundle multiple dependencies into one inside
    /// the [`RenderGraph`](super::RenderGraph).
    pub struct EmptyNode;

    impl Node for EmptyNode {
        fn run(
            &self,
            _graph: &mut RenderGraphContext,
            _render_context: &mut RenderContext,
            _state: &RenderState,
        ) -> Result<(), NodeRunError> {
            Ok(())
        }
    }