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

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    //! Utility for generating a tile pattern which can be used for masking.

    use crate::coords::{ViewRegion, WorldTileCoords, Zoom};
    use crate::render::camera::ViewProjection;
    use crate::render::resource::{BackingBufferDescriptor, BufferPool, Queue};
    use crate::render::shaders::{ShaderFeatureStyle, ShaderLayerMetadata, ShaderTileMetadata};
    use cgmath::Matrix4;

    use crate::render::ShaderVertex;
    use crate::tessellation::IndexDataType;
    use std::marker::PhantomData;
    use std::mem::size_of;
    use std::ops::Range;

    /// The tile mask pattern assigns each tile a value which can be used for stencil testing.
    pub struct TileViewPattern<Q, B> {
        in_view: Vec<TileInView>,
        buffer: BackingBuffer<B>,
        phantom_q: PhantomData<Q>,
    }

    #[derive(Clone)]
    pub struct TileShape {
        pub zoom_factor: f64,

        pub coords: WorldTileCoords,

        pub transform: Matrix4<f64>,
        pub buffer_range: Range<wgpu::BufferAddress>,
    }

    impl TileShape {
        fn new(coords: WorldTileCoords, zoom: Zoom, index: u64) -> Self {
            const STRIDE: u64 = size_of::<ShaderTileMetadata>() as u64;
            Self {
                coords,
                zoom_factor: zoom.scale_to_tile(&coords),
                transform: coords.transform_for_zoom(zoom),
                buffer_range: index as u64 * STRIDE..(index as u64 + 1) * STRIDE,
            }
        }
    }

    #[derive(Clone)]
    pub struct TileInView {
        pub shape: TileShape,

        pub fallback: Option<TileShape>,
    }

    #[derive(Debug)]
    struct BackingBuffer<B> {
        /// The internal structure which is used for storage
        inner: B,
        /// The size of the `inner` buffer
        inner_size: wgpu::BufferAddress,
    }

    impl<B> BackingBuffer<B> {
        fn new(inner: B, inner_size: wgpu::BufferAddress) -> Self {
            Self { inner, inner_size }
        }
    }

    impl<Q: Queue<B>, B> TileViewPattern<Q, B> {
        pub fn new(buffer: BackingBufferDescriptor<B>) -> Self {
            Self {
                in_view: Vec::with_capacity(64),
                buffer: BackingBuffer::new(buffer.buffer, buffer.inner_size),
                phantom_q: Default::default(),
            }
        }

        #[tracing::instrument(skip_all)]
        pub fn update_pattern(
            &mut self,
            view_region: &ViewRegion,
            buffer_pool: &BufferPool<
                wgpu::Queue,
                wgpu::Buffer,
                ShaderVertex,
                IndexDataType,
                ShaderLayerMetadata,
                ShaderFeatureStyle,
            >,
            zoom: Zoom,
        ) {
            self.in_view.clear();

            let mut index = 0;

            let pool_index = buffer_pool.index();

            for coords in view_region.iter() {
                if coords.build_quad_key().is_none() {
                    continue;
                }

                let shape = TileShape::new(coords, zoom, index);

                index += 1;

                let fallback = {
                    if !pool_index.has_tile(&coords) {
                        if let Some(fallback_coords) = pool_index.get_tile_coords_fallback(&coords) {
                            tracing::trace!(
                                "Could not find data at {coords}. Falling back to {fallback_coords}"
                            );

                            let shape = TileShape::new(fallback_coords, zoom, index);

                            index += 1;
                            Some(shape)
                        } else {
                            None
                        }
                    } else {
                        None
                    }
                };

                self.in_view.push(TileInView { shape, fallback });
            }
        }

        pub fn iter(&self) -> impl Iterator<Item = &TileInView> + '_ {
            self.in_view.iter()
        }

        pub fn buffer(&self) -> &B {
            &self.buffer.inner
        }

        #[tracing::instrument(skip_all)]
        pub fn upload_pattern(&self, queue: &Q, view_proj: &ViewProjection) {
            let mut buffer = Vec::with_capacity(self.in_view.len());

            for tile in &self.in_view {
                buffer.push(ShaderTileMetadata {
                    // We are casting here from 64bit to 32bit, because 32bit is more performant and is
                    // better supported.
                    transform: view_proj
                        .to_model_view_projection(tile.shape.transform)
                        .downcast()
                        .into(),
                    zoom_factor: tile.shape.zoom_factor as f32,
                });

                if let Some(fallback_shape) = &tile.fallback {
                    buffer.push(ShaderTileMetadata {
                        // We are casting here from 64bit to 32bit, because 32bit is more performant and is
                        // better supported.
                        transform: view_proj
                            .to_model_view_projection(fallback_shape.transform)
                            .downcast()
                            .into(),
                        zoom_factor: fallback_shape.zoom_factor as f32,
                    });
                }
            }

            queue.write_buffer(
                &self.buffer.inner,
                0,
                bytemuck::cast_slice(buffer.as_slice()),
            );
        }

        pub fn stencil_reference_value(&self, world_coords: &WorldTileCoords) -> u8 {
            match (world_coords.x, world_coords.y) {
                (x, y) if x % 2 == 0 && y % 2 == 0 => 2,
                (x, y) if x % 2 == 0 && y % 2 != 0 => 1,
                (x, y) if x % 2 != 0 && y % 2 == 0 => 4,
                (x, y) if x % 2 != 0 && y % 2 != 0 => 3,
                _ => unreachable!(),
            }
        }
    }