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Array view instead of direct wasm memory access #53

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Array view instead of direct wasm memory access #53

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c1f0959
use js_sys::Uint8Array instead of as_ptr()
mike-kfed May 17, 2020
ce4efde
import of linear memory is not needed
mike-kfed May 17, 2020
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1 change: 1 addition & 0 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@ default = ["console_error_panic_hook"]
[dependencies]
cfg-if = "0.1.2"
wasm-bindgen = "0.2"
js-sys = "0.3"

# The `console_error_panic_hook` crate provides better debugging of panics by
# logging them with `console.error`. This is great for development, but requires
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20 changes: 8 additions & 12 deletions src/lib.rs
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Expand Up @@ -5,6 +5,7 @@ extern crate web_sys;
mod utils;

use std::fmt;
use std::mem;
use wasm_bindgen::prelude::*;
use web_sys::console;

Expand Down Expand Up @@ -71,17 +72,9 @@ impl Universe {
fn live_neighbor_count(&self, row: u32, column: u32) -> u8 {
let mut count = 0;

let north = if row == 0 {
self.height - 1
} else {
row - 1
};
let north = if row == 0 { self.height - 1 } else { row - 1 };

let south = if row == self.height - 1 {
0
} else {
row + 1
};
let south = if row == self.height - 1 { 0 } else { row + 1 };

let west = if column == 0 {
self.width - 1
Expand Down Expand Up @@ -208,8 +201,11 @@ impl Universe {
self.cells = (0..self.width * height).map(|_i| Cell::Dead).collect();
}

pub fn cells(&self) -> *const Cell {
self.cells.as_ptr()
pub fn cells(&self) -> js_sys::Uint8Array {
unsafe {
let u8_cells = mem::transmute::<&Vec<Cell>, &Vec<u8>>(&self.cells);
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I think this can avoid transmute here and instead cast the slice to pointer, convert the pointer, and construct a new slice from that:

    let u8_cells: &[u8] = unsafe {
        let ptr = self.cells.as_ptr() as *const u8;
        let bytelen = self.cells.len() * std::mem::size_of::<Cell>();
        std::slice::from_raw_parts(ptr, bytelen)
    };

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=98b83b545fce22aec8fdf4a5e2ed5c55

js_sys::Uint8Array::view(&u8_cells)
}
}

pub fn toggle_cell(&mut self, row: u32, column: u32) {
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4 changes: 1 addition & 3 deletions www/index.js
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@@ -1,5 +1,4 @@
import { Universe, Cell } from "wasm-game-of-life";
import { memory } from "wasm-game-of-life/wasm_game_of_life_bg";

const CELL_SIZE = 5; // px
const GRID_COLOR = "#CCCCCC";
Expand Down Expand Up @@ -126,8 +125,7 @@ const getIndex = (row, column) => {
};

const drawCells = () => {
const cellsPtr = universe.cells();
const cells = new Uint8Array(memory.buffer, cellsPtr, width * height);
const cells = universe.cells();

ctx.beginPath();

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