Creating the Snake
Let's take a look at the main component of the game: The snake. There are several ways to implement one.
To keep things tidy, I recommend you'd create a new file called snake.ts. This file contains two classes:
- The
Point- Holding X and Y coordinates - The
Snake- The actual snake implementation
The content is rather simple:
export class Point { constructor( public x: i32, public y: i32 ) {}
equals(other: Point): bool { return this.x == other.x && this.y == other.y }}
export class Snake { body: Array<Point> = [ new Point(2, 0), new Point(1, 0), new Point(0, 0) ] direction: Point = new Point(1, 0)}The snake class contains the body and the current direction of the snake instance. But it lacks any functionality for now.
In this section we will define a structure to hold our snake.
Create a new file called snake.h and fill it with the code-snippet below.
#pragma once
#include <stdint.h>
struct point { int16_t x; int16_t y;};
struct snake { struct point* body; struct point direction; uint16_t length;};The snake type contains the body and the current direction of the snake instance. We also need to define a point struct to hold the x and y coordinates of our snake body parts.
We need to fill out the implementation of the snake. Function declarations will be added to snake.h and the definitions to a new file called snake.c.
We will work on two functions, one to create the snake, and one to add a body part to the snake.
Add the following declarations to the bottom of the snake.h file:
void snake_create(struct snake *snake);void snake_push(struct snake *snake, struct point p);Then in the snake.c file, we need to include our header files:
#include "snake.h"#include "wasm4.h"#include <stdlib.h>The file stdlib.h is required for realloc. The snake_create function frees any previous snake body that may have been allocated and initializes the snake struct body pointer to NULL, and the length to 0.
void snake_create(struct snake *snake){ if(snake->body != NULL) { free(snake->body); snake->body = NULL; } snake->length = 0;}The snake_push function will use the realloc function to allocate memory for each snake body part and assign the passed point struct value to it. When realloc is passed a NULL pointer it behaves the same as malloc so we can forego a NULL pointer check and just use realloc. The result of realloc is stored in a temporary body variable, when it succeeds the snake->body pointer is updated and the point value set.
void snake_push(struct snake *snake, struct point p){ struct point* body = realloc(snake->body, sizeof body * (snake->length+1)); if(body) { snake->body = body; snake->body[snake->length++] = p; }}// TODO
If you've used Go in the past, this next section won't be too surprising for you. You'll create a new type for the snake with the required properties.
For this, create a new file an call it snake.go. Then fill it with the code-snippet below.
package main
type Point struct { X int Y int}
type Snake struct { Body []Point Direction Point}The snake type contains the body and the current direction of the snake instance. But it lacks any functionality for now.
BuiltIn Type
Go offers a buildIn type for points. It's in image.
Creating our own type reduces the size of the cart.
To keep things tidy, I recommend you'd create a new file called snake.nelua. This file contains two records:
- The
Point- Holding X and Y coordinates - The
Snake- The actual snake implementation
The content is rather simple:
require "wasm4"local sequence = require "sequence"
local snake = @record{}
local snake.Point = @record{ x: int32, y: int32,}
local Point = snake.Point
local snake.Snake = @record{ body: sequence(Point), direction: Point,}
local Snake = snake.Snake
function Snake.init(): Snake return Snake{ body = { { x = 2, y = 0 }, { x = 1, y = 0 }, { x = 0, y = 0 }, }, direction = { x = 1, y = 0 }, }end
return snakeThe snake record contains the body and the current direction of the snake instance. But it lacks any functionality for now.
// TODO
// TODO
// TODO
To keep things tidy, I recommend to create a new file called snake.rs.
This file contains two structs:
- The
Point- Holdsxandycoordinates. - The
Snake- The actual snake implementation.
Snake has an associated function new that returns a brand new snake.
We have also defined few derivable traits to Point:
PartialEqandEqadd the==operator to perform an equality checks betweenPointinstances.CloneandCopysimplify use ofPointinstance.
You can learn more about these traits in the rust-book:
#[derive(Clone, Copy, PartialEq, Eq)]pub struct Point { pub x: i32, pub y: i32,}
pub struct Snake { pub body: Vec<Point>, pub direction: Point,}
impl Snake { pub fn new() -> Self { Self { body: vec![ Point { x: 2, y: 0 }, Point { x: 1, y: 0 }, Point { x: 0, y: 0 }, ], direction: Point { x: 1, y: 0 }, } }}note
Don't forget to declare this module in lib.rs.
mod snake;Unfortunately, the WebAssembly text format has no way to create classes or structs. The only way to lay out the stack structure is by manually allocating memory for the snake structure.
We'll pretend as though we have the following types. Note that they are not valid WebAssembly text definitions:
(; = 8 bytes typedef struct { i32 x; i32 y; } Point;
= 3200 bytes typedef Point Body[400];
= 3212 bytes typedef { Point direction; i32 body_length; Body body; } Snake;;)We'll place these values in linear memory starting at 0x19a0, which is the start of the region mapped for use by the game:
;; snake.direction = 0x19a0;; snake.body_length = 0x19a8;; snake.body = 0x19acLet's start the snake with 3 points: (2, 0), (1, 0), (0, 0). The snake's initial direction will be moving left, (1, 0).
(data (i32.const 0x19a0) "\01\00\00\00" "\00\00\00\00" ;; direction (1, 0) "\03\00\00\00" ;; body_length 3 "\02\00\00\00" "\00\00\00\00" ;; body[0] = (2, 0) "\01\00\00\00" "\00\00\00\00" ;; body[1] = (1, 0) "\00\00\00\00" "\00\00\00\00" ;; body[2] = (0, 0))To keep things tidy, I recommend you'd create a new file called snake.zig. This file contains two structs:
- The
Point- Holding X and Y coordinates - The
Snake- The actual snake implementation
The content is rather simple:
const std = @import("std");
pub const Point = struct { x: i32, y: i32,
pub fn init(x: i32, y: i32) Point { return .{ .x = x, .y = y, }; }
pub fn equals(this: Point, other: Point) bool { return this.x == other.x and this.y == other.y; }};
pub const Snake = struct { body: std.BoundedArray(Point, 400), direction: Point,
pub fn init() Snake { return .{ .body = std.BoundedArray(Point, 400).fromSlice(&.{ Point.init(2, 0), Point.init(1, 0), Point.init(0, 0), }) catch @panic("couldn't init snake body"), .direction = Point.init(1, 0), }; }};The snake class contains the body and the current direction of the snake instance. But it lacks any functionality for now.