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

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    use super::{NodeState, RenderGraph, SlotInfos, SlotLabel, SlotType, SlotValue};
    use crate::render::resource::TextureView;
    use std::borrow::Cow;
    use thiserror::Error;

    /// A command that signals the graph runner to run the sub graph corresponding to the `name`
    /// with the specified `inputs` next.
    pub struct RunSubGraph {
        pub name: Cow<'static, str>,
        pub inputs: Vec<SlotValue>,
    }

    /// The context with all graph information required to run a [`Node`](super::Node).
    /// This context is created for each node by the `RenderGraphRunner`.
    ///
    /// The slot input can be read from here and the outputs must be written back to the context for
    /// passing them onto the next node.
    ///
    /// Sub graphs can be queued for running by adding a [`RunSubGraph`] command to the context.
    /// After the node has finished running the graph runner is responsible for executing the sub graphs.
    pub struct RenderGraphContext<'a> {
        graph: &'a RenderGraph,
        node: &'a NodeState,
        inputs: &'a [SlotValue],
        outputs: &'a mut [Option<SlotValue>],
        run_sub_graphs: Vec<RunSubGraph>,
    }

    impl<'a> RenderGraphContext<'a> {
        /// Creates a new render graph context for the `node`.
        pub fn new(
            graph: &'a RenderGraph,
            node: &'a NodeState,
            inputs: &'a [SlotValue],
            outputs: &'a mut [Option<SlotValue>],
        ) -> Self {
            Self {
                graph,
                node,
                inputs,
                outputs,
                run_sub_graphs: Vec::new(),
            }
        }

        /// Returns the input slot values for the node.
        #[inline]
        pub fn inputs(&self) -> &[SlotValue] {
            self.inputs
        }

        /// Returns the [`SlotInfos`] of the inputs.
        pub fn input_info(&self) -> &SlotInfos {
            &self.node.input_slots
        }

        /// Returns the [`SlotInfos`] of the outputs.
        pub fn output_info(&self) -> &SlotInfos {
            &self.node.output_slots
        }

        /// Retrieves the input slot value referenced by the `label`.
        pub fn get_input(&self, label: impl Into<SlotLabel>) -> Result<&SlotValue, InputSlotError> {
            let label = label.into();
            let index = self
                .input_info()
                .get_slot_index(label.clone())
                .ok_or(InputSlotError::InvalidSlot(label))?;
            Ok(&self.inputs[index])
        }

        /// Retrieves the input slot value referenced by the `label` as a [`TextureView`].
        pub fn get_input_texture(
            &self,
            label: impl Into<SlotLabel>,
        ) -> Result<&TextureView, InputSlotError> {
            let label = label.into();
            match self.get_input(label.clone())? {
                SlotValue::TextureView(value) => Ok(value),
                value => Err(InputSlotError::MismatchedSlotType {
                    label,
                    actual: value.slot_type(),
                    expected: SlotType::TextureView,
                }),
            }
        }

        /// Retrieves the input slot value referenced by the `label` as a [`Sampler`].
        pub fn get_input_sampler(
            &self,
            label: impl Into<SlotLabel>,
        ) -> Result<&wgpu::Sampler, InputSlotError> {
            let label = label.into();
            match self.get_input(label.clone())? {
                SlotValue::Sampler(value) => Ok(value),
                value => Err(InputSlotError::MismatchedSlotType {
                    label,
                    actual: value.slot_type(),
                    expected: SlotType::Sampler,
                }),
            }
        }

        /// Retrieves the input slot value referenced by the `label` as a [`Buffer`].
        pub fn get_input_buffer(
            &self,
            label: impl Into<SlotLabel>,
        ) -> Result<&wgpu::Buffer, InputSlotError> {
            let label = label.into();
            match self.get_input(label.clone())? {
                SlotValue::Buffer(value) => Ok(value),
                value => Err(InputSlotError::MismatchedSlotType {
                    label,
                    actual: value.slot_type(),
                    expected: SlotType::Buffer,
                }),
            }
        }

        /// Sets the output slot value referenced by the `label`.
        pub fn set_output(
            &mut self,
            label: impl Into<SlotLabel>,
            value: impl Into<SlotValue>,
        ) -> Result<(), OutputSlotError> {
            let label = label.into();
            let value = value.into();
            let slot_index = self
                .output_info()
                .get_slot_index(label.clone())
                .ok_or_else(|| OutputSlotError::InvalidSlot(label.clone()))?;
            let slot = self
                .output_info()
                .get_slot(slot_index)
                .expect("slot is valid");
            if value.slot_type() != slot.slot_type {
                return Err(OutputSlotError::MismatchedSlotType {
                    label,
                    actual: slot.slot_type,
                    expected: value.slot_type(),
                });
            }
            self.outputs[slot_index] = Some(value);
            Ok(())
        }

        /// Queues up a sub graph for execution after the node has finished running.
        pub fn run_sub_graph(
            &mut self,
            name: impl Into<Cow<'static, str>>,
            inputs: Vec<SlotValue>,
        ) -> Result<(), RunSubGraphError> {
            let name = name.into();
            let sub_graph = self
                .graph
                .get_sub_graph(&name)
                .ok_or_else(|| RunSubGraphError::MissingSubGraph(name.clone()))?;
            if let Some(input_node) = sub_graph.input_node() {
                for (i, input_slot) in input_node.input_slots.iter().enumerate() {
                    if let Some(input_value) = inputs.get(i) {
                        if input_slot.slot_type != input_value.slot_type() {
                            return Err(RunSubGraphError::MismatchedInputSlotType {
                                graph_name: name,
                                slot_index: i,
                                actual: input_value.slot_type(),
                                expected: input_slot.slot_type,
                                label: input_slot.name.clone().into(),
                            });
                        }
                    } else {
                        return Err(RunSubGraphError::MissingInput {
                            slot_index: i,
                            slot_name: input_slot.name.clone(),
                            graph_name: name,
                        });
                    }
                }
            } else if !inputs.is_empty() {
                return Err(RunSubGraphError::SubGraphHasNoInputs(name));
            }

            self.run_sub_graphs.push(RunSubGraph { name, inputs });

            Ok(())
        }

        /// Finishes the context for this [`Node`](super::Node) by
        /// returning the sub graphs to run next.
        pub fn finish(self) -> Vec<RunSubGraph> {
            self.run_sub_graphs
        }
    }

    #[derive(Error, Debug, Eq, PartialEq)]
    pub enum RunSubGraphError {
        #[error("attempted to run sub-graph `{0}`, but it does not exist")]
        MissingSubGraph(Cow<'static, str>),
        #[error("attempted to pass inputs to sub-graph `{0}`, which has no input slots")]
        SubGraphHasNoInputs(Cow<'static, str>),
        #[error("sub graph (name: `{graph_name:?}`) could not be run because slot `{slot_name}` at index {slot_index} has no value")]
        MissingInput {
            slot_index: usize,
            slot_name: Cow<'static, str>,
            graph_name: Cow<'static, str>,
        },
        #[error("attempted to use the wrong type for input slot")]
        MismatchedInputSlotType {
            graph_name: Cow<'static, str>,
            slot_index: usize,
            label: SlotLabel,
            expected: SlotType,
            actual: SlotType,
        },
    }

    #[derive(Error, Debug, Eq, PartialEq)]
    pub enum OutputSlotError {
        #[error("output slot `{0:?}` does not exist")]
        InvalidSlot(SlotLabel),
        #[error("attempted to output a value of type `{actual}` to output slot `{label:?}`, which has type `{expected}`")]
        MismatchedSlotType {
            label: SlotLabel,
            expected: SlotType,
            actual: SlotType,
        },
    }

    #[derive(Error, Debug, Eq, PartialEq)]
    pub enum InputSlotError {
        #[error("input slot `{0:?}` does not exist")]
        InvalidSlot(SlotLabel),
        #[error("attempted to retrieve a value of type `{actual}` from input slot `{label:?}`, which has type `{expected}`")]
        MismatchedSlotType {
            label: SlotLabel,
            expected: SlotType,
            actual: SlotType,
        },
    }