2 files changed, 93 insertions, 69 deletions

diff --git a/src/proc_gen/herringbone.rs b/src/proc_gen/herringbone.rs
index e8569c8..0a67b0c 100644
--- a/src/proc_gen/herringbone.rs
+++ b/src/proc_gen/herringbone.rs
@@ -3,22 +3,27 @@ use glam::IVec2;
 
 use crate::proc_gen::tileset_loader::TileOrientation;
 
-fn tile_starting_at(grid: IVec2) -> Option<TileOrientation> {
+pub fn split_position(pixel: IVec2, short: i32) -> (IVec2, IVec2, TileOrientation) {
+    let grid = pixel.div_euclid(IVec2::splat(short));
+    let local = pixel.rem_euclid(IVec2::splat(short));
+
     match (grid.x - grid.y).rem_euclid(4) {
-        // 1 is the right half of the horizontal tile starting at 0,
-        // 2 is the bottom half of the vertical tile starting at 3
-        0 => Some(TileOrientation::Horizontal),
-        3 => Some(TileOrientation::Vertical),
-        _ => None,
+        0 => (grid, local, TileOrientation::Horizontal),
+        1 => (
+            grid - IVec2::X,
+            local + IVec2::new(short, 0),
+            TileOrientation::Horizontal,
+        ),
+        3 => (grid, local, TileOrientation::Vertical),
+        2 => (
+            grid - IVec2::Y,
+            local + IVec2::new(0, short),
+            TileOrientation::Vertical,
+        ),
+        _ => unreachable!(),
     }
 }
 
-pub fn tiles_overlapping(min: IVec2, max: IVec2) -> impl Iterator<Item = (IVec2, TileOrientation)> {
-    ((min.y - 1)..max.y)
-        .flat_map(move |y| ((min.x - 1)..max.x).map(move |x| IVec2::new(x, y)))
-        .filter_map(|grid| tile_starting_at(grid).map(|orientation| (grid, orientation)))
-}
-
 // better "%" for hashes since it prefers the high bits
 #[inline]
 fn reduce(h: u32, n: usize) -> usize {
diff --git a/src/proc_gen/mod.rs b/src/proc_gen/mod.rs
index caec241..4a1003a 100644
--- a/src/proc_gen/mod.rs
+++ b/src/proc_gen/mod.rs
@@ -6,92 +6,111 @@ use glam::IVec2;
 use crate::{
     config::{CHUNK_SIZE, TILESET_SCALING},
     proc_gen::{
-        herringbone::{tiles_overlapping, variant_index},
-        tileset_loader::{Tile, TileOrientation, Tileset, load_tileset},
+        herringbone::{split_position, variant_index},
+        tileset_loader::{Tile, TileOrientation, Tileset, TilesetPixelType, load_tileset},
     },
     sim::{cell::Cell, cell_manager::chunk::Chunk, entity::EntityDef},
 };
 
-pub struct TileCells {
-    pub size: IVec2,
-    pub cells: Vec<Cell>,
+#[inline]
+fn lerp(a: f32, b: f32, t: f32) -> f32 {
+    a + (b - a) * t
+}
+
+const CHUNK_PIXELS: i32 = CHUNK_SIZE / TILESET_SCALING;
+const PIXELS_NEIGHBOURHOOD_SIZE: i32 = CHUNK_PIXELS + 2;
+
+// 2d slice of solidity; chunk + 1 margin
+struct BiomeChunkContext {
+    instantaneous_solidity: [f32; (PIXELS_NEIGHBOURHOOD_SIZE * PIXELS_NEIGHBOURHOOD_SIZE) as usize],
+}
+
+impl BiomeChunkContext {
+    fn lerped_solidity_at(&self, local: IVec2) -> f32 {
+        // pixel coord centre of cell coord local
+        let pixel_position = (local.as_vec2() + 0.5) / TILESET_SCALING as f32 + 0.5;
+        let pixel = pixel_position.floor();
+        // distance from the current pixel to the centre of the cell
+        let frac = pixel_position - pixel;
+        let pixel = pixel.as_ivec2();
+
+        let at = |dx, dy| {
+            self.instantaneous_solidity
+                [((pixel.x + dx) + (pixel.y + dy) * PIXELS_NEIGHBOURHOOD_SIZE) as usize]
+        };
+
+        // linearly interpolate between the solidity of the horizontal cells above and below according to the fractional x component
+        let top = lerp(at(0, 0), at(1, 0), frac.x);
+        let bottom = lerp(at(0, 1), at(1, 1), frac.x);
+
+        // and then interpolate between those according to the y component
+        lerp(top, bottom, frac.y) - 0.5
+    }
 }
 
 pub trait Biome {
-    fn derive_world_from_tile(&self, tile: &Tile) -> TileCells;
-    fn derive_entities_from_tile(&self, tile: &Tile) -> Vec<EntityDef> {
+    fn cell(&self, solidity: f32, world: IVec2) -> Cell;
+
+    fn derive_entities_from_tile(&self, _tile: &Tile) -> Vec<EntityDef> {
         Vec::new()
     }
 }
 
 pub struct TilesetWorldGenerator {
     tileset: Tileset,
-    horizontal_tiles: Vec<TileCells>,
-    vertical_tiles: Vec<TileCells>,
+    biome: Box<dyn Biome>,
 }
 
 impl TilesetWorldGenerator {
-    pub fn new(tileset_path: &str, biome: &dyn Biome) -> Self {
-        let tileset = load_tileset(tileset_path);
-
-        let horizontal_tiles = tileset
-            .horizontal_tiles
-            .iter()
-            .map(|tile| biome.derive_world_from_tile(tile))
-            .collect();
-        let vertical_tiles = tileset
-            .vertical_tiles
-            .iter()
-            .map(|tile| biome.derive_world_from_tile(tile))
-            .collect();
-
+    pub fn new(tileset_path: &str, biome: Box<dyn Biome>) -> Self {
         TilesetWorldGenerator {
-            tileset,
-            horizontal_tiles,
-            vertical_tiles,
+            tileset: load_tileset(tileset_path),
+            biome,
         }
     }
 
-    fn grid_size(&self) -> IVec2 {
-        IVec2::splat(self.tileset.dimensions.short as i32 * TILESET_SCALING)
-    }
+    fn pixel_at(&self, pixel: IVec2) -> TilesetPixelType {
+        let (grid, local, orientation) =
+            split_position(pixel, self.tileset.dimensions.short as i32);
 
-    fn tile_at(&self, grid: IVec2, orientation: TileOrientation) -> &TileCells {
         let tiles = match orientation {
-            TileOrientation::Horizontal => &self.horizontal_tiles,
-            TileOrientation::Vertical => &self.vertical_tiles,
+            TileOrientation::Horizontal => &self.tileset.horizontal_tiles,
+            TileOrientation::Vertical => &self.tileset.vertical_tiles,
         };
-        &tiles[variant_index(grid, tiles.len())]
+
+        tiles[variant_index(grid, tiles.len())].pixel_at(local)
     }
 
-    pub fn generate_chunk(&self, chunk_position: IVec2) -> Chunk {
-        let mut chunk = Chunk::void();
+    fn structure_around(&self, chunk_position: IVec2) -> BiomeChunkContext {
+        let origin = chunk_position * CHUNK_PIXELS - 1;
+        let mut occupancy = [0.0; (PIXELS_NEIGHBOURHOOD_SIZE * PIXELS_NEIGHBOURHOOD_SIZE) as usize];
 
-        let chunk_min = chunk_position * CHUNK_SIZE;
-        let chunk_max = chunk_min + CHUNK_SIZE;
-
-        let grid = self.grid_size();
-        let tiles = tiles_overlapping(
-            chunk_min.div_euclid(grid),
-            (chunk_max - 1).div_euclid(grid) + 1,
-        );
+        for y in 0..PIXELS_NEIGHBOURHOOD_SIZE {
+            for x in 0..PIXELS_NEIGHBOURHOOD_SIZE {
+                occupancy[(x + y * PIXELS_NEIGHBOURHOOD_SIZE) as usize] =
+                    match self.pixel_at(origin + IVec2::new(x, y)) {
+                        TilesetPixelType::Void => 0.0,
+                        TilesetPixelType::Terrain => 1.0,
+                    };
+            }
+        }
 
-        for (grid_position, orientation) in tiles {
-            let tile = self.tile_at(grid_position, orientation);
-            let tile_min = grid_position * grid;
+        BiomeChunkContext {
+            instantaneous_solidity: occupancy,
+        }
+    }
 
-            // subset of tile in chunk
-            let min = tile_min.max(chunk_min);
-            let max = (tile_min + tile.size).min(chunk_max);
-            if min.x >= max.x {
-                continue;
-            }
-            let width = (max.x - min.x) as usize;
+    pub fn generate_chunk(&self, chunk_position: IVec2) -> Chunk {
+        let mut chunk = Chunk::void();
+        let structure = self.structure_around(chunk_position);
+        let chunk_min = chunk_position * CHUNK_SIZE;
 
-            for y in min.y..max.y {
-                let src = ((y - tile_min.y) * tile.size.x + (min.x - tile_min.x)) as usize;
-                let dst = ((y - chunk_min.y) * CHUNK_SIZE + (min.x - chunk_min.x)) as usize;
-                chunk.cells[dst..dst + width].copy_from_slice(&tile.cells[src..src + width]);
+        for y in 0..CHUNK_SIZE {
+            for x in 0..CHUNK_SIZE {
+                let local = IVec2::new(x, y);
+                chunk.cells[(x + y * CHUNK_SIZE) as usize] = self
+                    .biome
+                    .cell(structure.lerped_solidity_at(local), chunk_min + local);
             }
         }