From 167e31655b63aa4d4548532cf0410cea9fd145ca Mon Sep 17 00:00:00 2001
From: Kai Stevenson <kai@kaistevenson.com>
Date: Sun, 9 Aug 2026 16:30:29 -0700
Subject: drawing

---
 src/sim/board.rs     | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/sim/materials.rs | 22 ++++++++++++++++
 src/sim/mod.rs       |  4 +++
 src/sim/overlay.rs   | 50 ++++++++++++++++++++++++++++++++++++
 src/sim/sim.rs       |  3 +++
 5 files changed, 151 insertions(+)
 create mode 100644 src/sim/board.rs
 create mode 100644 src/sim/materials.rs
 create mode 100644 src/sim/mod.rs
 create mode 100644 src/sim/overlay.rs
 create mode 100644 src/sim/sim.rs

(limited to 'src/sim')

diff --git a/src/sim/board.rs b/src/sim/board.rs
new file mode 100644
index 0000000..4cc5756
--- /dev/null
+++ b/src/sim/board.rs
@@ -0,0 +1,72 @@
+use crate::config::{PIXEL_BUFFER_HEIGHT, PIXEL_BUFFER_WIDTH};
+
+type MaterialId = u16;
+
+#[derive(Clone, Copy)]
+pub struct Cell {
+    pub material: MaterialId,
+    pub velocity_x: i8,
+    pub velocity_y: i8,
+    pub flags: u8,
+}
+
+impl Cell {
+    fn empty() -> Cell {
+        Cell {
+            material: 0,
+            velocity_x: 0,
+            velocity_y: 0,
+            flags: 0,
+        }
+    }
+}
+
+pub struct Board {
+    pub size_x: u32,
+    pub size_y: u32,
+    pub cells: Vec<Cell>,
+}
+
+impl Board {
+    pub fn index_to_position(&self, idx: usize) -> (i32, i32) {
+        let y = idx / self.size_x as usize;
+        let x = idx % self.size_x as usize;
+        let board_x = x as i32 - self.size_x as i32 / 2;
+        let board_y = y as i32 - self.size_x as i32 / 2;
+        return (board_x, board_y);
+    }
+    pub fn set_cell_at_position(&mut self, x: i32, y: i32, c: Cell) {
+        // TODO: option?
+        let idx = self.position_to_index(x, y).unwrap();
+        self.cells[idx] = c;
+    }
+    pub fn cell_at_position(&self, x: i32, y: i32) -> Option<&Cell> {
+        Some(&self.cells[self.position_to_index(x, y)?])
+    }
+    pub fn position_to_index(&self, x: i32, y: i32) -> Option<usize> {
+        let board_x = x + self.size_x as i32 / 2;
+        let board_y = y + self.size_y as i32 / 2;
+
+        let on_board = board_x >= 0
+            && board_x < self.size_x as i32
+            && board_y >= 0
+            && board_y < self.size_y as i32;
+
+        if !on_board {
+            return None;
+        }
+
+        return Some((board_y * self.size_x as i32 + board_x) as usize);
+    }
+    pub fn empty() -> Board {
+        let size_x = PIXEL_BUFFER_WIDTH * 2;
+        let size_y = PIXEL_BUFFER_HEIGHT * 2;
+        let cells: Vec<Cell> = vec![Cell::empty(); (size_x * size_y) as usize];
+
+        Board {
+            size_x,
+            size_y,
+            cells,
+        }
+    }
+}
diff --git a/src/sim/materials.rs b/src/sim/materials.rs
new file mode 100644
index 0000000..13a45f3
--- /dev/null
+++ b/src/sim/materials.rs
@@ -0,0 +1,22 @@
+#[derive(Clone, Copy)]
+pub struct Material<'a> {
+    pub name: &'a str,
+    pub r: u8,
+    pub g: u8,
+    pub b: u8,
+}
+
+pub static MATERIALS: [Material; 2] = [
+    Material {
+        name: "Void",
+        r: 0x00,
+        g: 0x00,
+        b: 0x00,
+    },
+    Material {
+        name: "Sand",
+        r: 0xFF,
+        g: 0x00,
+        b: 0xFF,
+    },
+];
diff --git a/src/sim/mod.rs b/src/sim/mod.rs
new file mode 100644
index 0000000..2b29628
--- /dev/null
+++ b/src/sim/mod.rs
@@ -0,0 +1,4 @@
+pub mod board;
+pub mod materials;
+pub mod overlay;
+pub mod sim;
diff --git a/src/sim/overlay.rs b/src/sim/overlay.rs
new file mode 100644
index 0000000..36a810b
--- /dev/null
+++ b/src/sim/overlay.rs
@@ -0,0 +1,50 @@
+use crate::{Config, Input, sim::board::Board};
+
+pub fn create_compute_combined_overlay_offset(
+    board: &Board,
+    config: &Config,
+    input: &Input,
+) -> impl Fn(i32, i32) -> (u8, u8, u8, u8) {
+    |x: i32, y: i32| {
+        // could allow negative offsets too
+        let mut offset: (u8, u8, u8, u8) = (0x00, 0x00, 0x00, 0x00);
+
+        // bounds
+        // left
+        let xl = -((board.size_x / 2 + 1) as i32);
+        // right
+        let xu = (board.size_x / 2 + 1) as i32;
+        // bottom
+        let yl = -((board.size_y / 2 + 1) as i32);
+        // top
+        let yu = (board.size_y / 2 + 1) as i32;
+
+        if ((x == xl || x == xu) && (y <= yu && y >= yl))
+            || (y == yl || y == yu) && (x <= xu && x >= xl)
+        {
+            offset.0 = offset.0.saturating_add(0xFF);
+            offset.1 = offset.1.saturating_add(0xFF);
+            offset.2 = offset.2.saturating_add(0xFF);
+        }
+
+        // grid
+        if x % 30 == 0 || y % 30 == 0 {
+            offset.0 = offset.0.saturating_add(0x10);
+            offset.1 = offset.1.saturating_add(0x10);
+            offset.2 = offset.2.saturating_add(0x10);
+        }
+
+        // brush/selection
+        if (((x - input.last_mouse_pos_on_board.0).pow(2)
+            + (y - input.last_mouse_pos_on_board.1).pow(2)) as f32)
+            .sqrt()
+            < config.brush_size as f32
+        {
+            offset.0 = offset.0.saturating_add(0xAA);
+            offset.1 = offset.1.saturating_add(0x00);
+            offset.2 = offset.2.saturating_add(0xAA);
+        }
+
+        return offset;
+    }
+}
diff --git a/src/sim/sim.rs b/src/sim/sim.rs
new file mode 100644
index 0000000..bb68306
--- /dev/null
+++ b/src/sim/sim.rs
@@ -0,0 +1,3 @@
+use crate::Board;
+
+fn sim_tick(board: Board, seqno: u64) {}
-- 
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