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

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    //! The main render pass for this application.
    //!
    //! Right now there is only one render graph. A use case for multiple render passes would be
    //! [shadows](https://www.raywenderlich.com/books/metal-by-tutorials/v2.0/chapters/14-multipass-deferred-rendering).

    use std::ops::Deref;

    use wgpu::StoreOp;

    use crate::{
        render::{
            draw_graph,
            graph::{Node, NodeRunError, RenderContext, RenderGraphContext, SlotInfo},
            render_phase::{LayerItem, RenderPhase, TileMaskItem},
            resource::TrackedRenderPass,
            Eventually::Initialized,
            RenderResources,
        },
        tcs::world::World,
    };

    pub struct MainPassNode {}

    impl MainPassNode {
        pub fn new() -> Self {
            Self {}
        }
    }

    impl Node for MainPassNode {
        fn input(&self) -> Vec<SlotInfo> {
            vec![]
        }

        fn update(&mut self, _state: &mut RenderResources) {}

        fn run(
            &self,
            _graph: &mut RenderGraphContext,
            render_context: &mut RenderContext,
            state: &RenderResources,
            world: &World,
        ) -> Result<(), NodeRunError> {
            let Initialized(render_target) = &state.render_target else {
                return Ok(());
            };
            let Initialized(multisampling_texture) = &state.multisampling_texture else {
                return Ok(());
            };
            let Initialized(depth_texture) = &state.depth_texture else {
                return Ok(());
            };

            let color_attachment = if let Some(texture) = multisampling_texture {
                wgpu::RenderPassColorAttachment {
                    view: &texture.view,
                    ops: wgpu::Operations {
                        load: wgpu::LoadOp::Clear(wgpu::Color::WHITE),
                        store: StoreOp::Store,
                    },
                    resolve_target: Some(render_target.deref()),
                }
            } else {
                wgpu::RenderPassColorAttachment {
                    view: render_target.deref(),
                    ops: wgpu::Operations {
                        load: wgpu::LoadOp::Clear(wgpu::Color::WHITE),
                        store: StoreOp::Store,
                    },
                    resolve_target: None,
                }
            };

            let render_pass =
                render_context
                    .command_encoder
                    .begin_render_pass(&wgpu::RenderPassDescriptor {
                        label: Some("main_pass"),
                        color_attachments: &[Some(color_attachment)],
                        depth_stencil_attachment: Some(wgpu::RenderPassDepthStencilAttachment {
                            view: &depth_texture.view,
                            depth_ops: Some(wgpu::Operations {
                                load: wgpu::LoadOp::Clear(0.0),
                                store: StoreOp::Store,
                            }),
                            stencil_ops: Some(wgpu::Operations {
                                load: wgpu::LoadOp::Clear(0),
                                store: StoreOp::Store,
                            }),
                        }),
                        timestamp_writes: None,
                        occlusion_query_set: None,
                    });

            let mut tracked_pass = TrackedRenderPass::new(render_pass);

            if let Some(mask_items) = world.resources.get::<RenderPhase<TileMaskItem>>() {
                log::trace!("RenderPhase<TileMaskItem>::size() = {}", mask_items.size());
                for item in mask_items {
                    item.draw_function.draw(&mut tracked_pass, world, item);
                }
            }

            if let Some(layer_items) = world.resources.get::<RenderPhase<LayerItem>>() {
                log::trace!("RenderPhase<LayerItem>::size() = {}", layer_items.size());
                for item in layer_items {
                    item.draw_function.draw(&mut tracked_pass, world, item);
                }
            }

            Ok(())
        }
    }

    pub struct MainPassDriverNode;

    impl Node for MainPassDriverNode {
        fn run(
            &self,
            graph: &mut RenderGraphContext,
            _render_context: &mut RenderContext,
            _resources: &RenderResources,
            _world: &World,
        ) -> Result<(), NodeRunError> {
            graph.run_sub_graph(draw_graph::NAME, vec![])?;

            Ok(())
        }
    }