# graph_runner.rs - source
Source of the Rust file `maplibre/src/render/graph_runner.rs`.

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    46
    47
    48
    49
    50
    51
    52
    53
    54
    55
    56
    57
    58
    59
    60
    61
    62
    63
    64
    65
    66
    67
    68
    69
    70
    71
    72
    73
    74
    75
    76
    77
    78
    79
    80
    81
    82
    83
    84
    85
    86
    87
    88
    89
    90
    91
    92
    93
    94
    95
    96
    97
    98
    99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223

    //! Executes a [`RenderGraph`]

    use std::{
        borrow::Cow,
        collections::{HashMap, VecDeque},
    };

    use log::error;
    use smallvec::{smallvec, SmallVec};
    use thiserror::Error;

    use crate::{
        render::{
            graph::{
                Edge, NodeId, NodeRunError, NodeState, RenderContext, RenderGraph, RenderGraphContext,
                SlotLabel, SlotType, SlotValue,
            },
            RenderResources,
        },
        tcs::world::World,
    };

    pub(crate) struct RenderGraphRunner;

    #[derive(Error, Debug)]
    pub enum RenderGraphRunnerError {
        #[error(transparent)]
        NodeRunError(#[from] NodeRunError),
        #[error("node output slot not set (index {slot_index}, name {slot_name})")]
        EmptyNodeOutputSlot {
            type_name: &'static str,
            slot_index: usize,
            slot_name: Cow<'static, str>,
        },
        #[error("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: Option<Cow<'static, str>>,
        },
        #[error("attempted to use the wrong type for input slot")]
        MismatchedInputSlotType {
            slot_index: usize,
            label: SlotLabel,
            expected: SlotType,
            actual: SlotType,
        },
    }

    impl RenderGraphRunner {
        pub fn run(
            graph: &RenderGraph,
            device: &wgpu::Device,
            queue: &wgpu::Queue,
            state: &RenderResources,
            world: &World,
        ) -> Result<(), RenderGraphRunnerError> {
            let command_encoder =
                device.create_command_encoder(&wgpu::CommandEncoderDescriptor::default());
            let mut render_context = RenderContext {
                device,
                command_encoder,
            };

            Self::run_graph(graph, None, &mut render_context, state, world, &[])?;
            {
                #[cfg(feature = "trace")]
                let _span = tracing::info_span!("submit_graph_commands").entered();
                queue.submit(vec![render_context.command_encoder.finish()]);
            }
            Ok(())
        }

        fn run_graph(
            graph: &RenderGraph,
            graph_name: Option<Cow<'static, str>>,
            render_context: &mut RenderContext,
            state: &RenderResources,
            world: &World,
            inputs: &[SlotValue],
        ) -> Result<(), RenderGraphRunnerError> {
            let mut node_outputs: HashMap<NodeId, SmallVec<[SlotValue; 4]>> = HashMap::default();
            #[cfg(feature = "trace")]
            let span = if let Some(name) = &graph_name {
                tracing::info_span!("run_graph", name = name.as_ref())
            } else {
                tracing::info_span!("run_graph", name = "main_graph")
            };
            #[cfg(feature = "trace")]
            let _guard = span.enter();

            // Queue up nodes without inputs, which can be run immediately
            let mut node_queue: VecDeque<&NodeState> = graph
                .iter_nodes()
                .filter(|node| node.input_slots.is_empty())
                .collect();

            // pass inputs into the graph
            if let Some(input_node) = graph.input_node() {
                let mut input_values: SmallVec<[SlotValue; 4]> = SmallVec::new();
                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(RenderGraphRunnerError::MismatchedInputSlotType {
                                slot_index: i,
                                actual: input_value.slot_type(),
                                expected: input_slot.slot_type,
                                label: input_slot.name.clone().into(),
                            });
                        } else {
                            input_values.push(input_value.clone());
                        }
                    } else {
                        return Err(RenderGraphRunnerError::MissingInput {
                            slot_index: i,
                            slot_name: input_slot.name.clone(),
                            graph_name: graph_name.clone(),
                        });
                    }
                }

                node_outputs.insert(input_node.id, input_values);

                for (_, node_state) in graph.iter_node_outputs(input_node.id).expect("node exists") {
                    node_queue.push_front(node_state);
                }
            }

            'handle_node: while let Some(node_state) = node_queue.pop_back() {
                // skip nodes that are already processed
                if node_outputs.contains_key(&node_state.id) {
                    continue;
                }

                let mut slot_indices_and_inputs: SmallVec<[(usize, SlotValue); 4]> = SmallVec::new();
                // check if all dependencies have finished running
                for (edge, input_node) in graph
                    .iter_node_inputs(node_state.id)
                    .expect("node is in graph")
                {
                    match edge {
                        Edge::SlotEdge {
                            output_index,
                            input_index,
                            ..
                        } => {
                            if let Some(outputs) = node_outputs.get(&input_node.id) {
                                slot_indices_and_inputs
                                    .push((*input_index, outputs[*output_index].clone()));
                            } else {
                                node_queue.push_front(node_state);
                                continue 'handle_node;
                            }
                        }
                        Edge::NodeEdge { .. } => {
                            if !node_outputs.contains_key(&input_node.id) {
                                node_queue.push_front(node_state);
                                continue 'handle_node;
                            }
                        }
                    }
                }

                // construct final sorted input list
                slot_indices_and_inputs.sort_by_key(|(index, _)| *index);
                let inputs: SmallVec<[SlotValue; 4]> = slot_indices_and_inputs
                    .into_iter()
                    .map(|(_, value)| value)
                    .collect();

                assert_eq!(inputs.len(), node_state.input_slots.len());

                let mut outputs: SmallVec<[Option<SlotValue>; 4]> =
                    smallvec![None; node_state.output_slots.len()];
                {
                    let mut context = RenderGraphContext::new(graph, node_state, &inputs, &mut outputs);
                    {
                        #[cfg(feature = "trace")]
                        let _span = tracing::info_span!("node", name = node_state.type_name).entered();

                        node_state
                            .node
                            .run(&mut context, render_context, state, world)?;
                    }

                    for run_sub_graph in context.finish() {
                        let sub_graph = graph
                            .get_sub_graph(&run_sub_graph.name)
                            .expect("sub graph exists because it was validated when queued.");
                        Self::run_graph(
                            sub_graph,
                            Some(run_sub_graph.name),
                            render_context,
                            state,
                            world,
                            &run_sub_graph.inputs,
                        )?;
                    }
                }

                let mut values: SmallVec<[SlotValue; 4]> = SmallVec::new();
                for (i, output) in outputs.into_iter().enumerate() {
                    if let Some(value) = output {
                        values.push(value);
                    } else {
                        let empty_slot = node_state.output_slots.get_slot(i).unwrap();
                        return Err(RenderGraphRunnerError::EmptyNodeOutputSlot {
                            type_name: node_state.type_name,
                            slot_index: i,
                            slot_name: empty_slot.name.clone(),
                        });
                    }
                }
                node_outputs.insert(node_state.id, values);

                for (_, node_state) in graph.iter_node_outputs(node_state.id).expect("node exists") {
                    node_queue.push_front(node_state);
                }
            }

            Ok(())
        }
    }