ggez游戏开发入门

内容来自github，介绍了ggez的基本使用和框架。还是比较简单明了的，就是有一个state保存游戏状态，以及update和draw两个方法函数。

完整代码如下：

use ggez::*;

struct State {
    dt: std::time::Duration,
}

impl ggez::event::EventHandler<GameError> for State {
  fn update(&mut self, ctx: &mut Context) -> GameResult {
    self.dt = timer::delta(ctx);
    Ok(())
  }
  fn draw(&mut self, _ctx: &mut Context) -> GameResult {
    println!("Hello ggez! dt = {}ns", self.dt.as_nanos());
    Ok(())
  }
}

fn main() {
    let state = State {
        dt: std::time::Duration::new(0, 0),
    };

    let c = conf::Conf::new();
    let (ctx, event_loop) = ContextBuilder::new("hello_ggez", "awesome_person")
        .default_conf(c)
        .build()
        .unwrap();

    event::run(ctx, event_loop, state);        
}

👋 Hello `ggez`!

This is a guide to create a program that prints Hello ggez! dt = 78986ns every frame.

At the end of this guide you will:

Have created a simple program using ggez
Know the basic scaffolding of a ggez program

⚠ Prerequisites

Rust

Rust will need to be installed. Follow Rust's guides for installing the latest stable version. You did know this was a Rust library right? 😉

🛠 Project Setup

Cargo Crate

Open up your terminal and make sure it is in the location where you want to create your new project folder.

cargo new --bin hello_ggez
cd hello_ggez

Open up Cargo.toml with a text editor and add ggez as a dependency:

[package]
name = "hello_ggez"
version = "0.1.0"
# Replace with your name and email
authors = ["Awesome Person [email protected]"]

[dependencies]
ggez = "0.6"

✔ Check Project Setup

Test to make sure everything is correct by running cargo run.

Be patient. This can take a while on the first run. Subsequent builds will be much faster. Be sure it says Hello, world! at the bottom before continuing.

ggez

We have successfully compiled ggez, but we haven't used it yet! What we have currently is the canonical Rust hello world. Let's change that and create a more appropriate hello world for ggez. It is why we're here after all.

First we'll tell Rust we want to use ggez. Add this to the top of your src/main.rs:

use ggez::*;

Now we're cooking with ggez.

Loop

All games have a loop. Often the loop is referred to as a game loop.

Game loops are responsible for:

Handling events such as keyboard, mouse, closing window, etc.
Updating state such as player position, health, etc.
Drawing shapes, images, etc.

ggez provides an EventHandler as the default recommended interface to its internal loop to use in our games. Thanks ggez!

You might have noticed EventHandler is a Rust Trait. This means it is intended to be implemented on a struct. There are quite a few callbacks defined on the Trait, but only 2 are required: update and draw.

Let's add EventHandler to our src/main.rs file:

struct State {}

impl ggez::event::EventHandler<GameError> for State {
  fn update(&mut self, ctx: &mut Context) -> GameResult {
      Ok(())
  }
  fn draw(&mut self, ctx: &mut Context) -> GameResult {
      Ok(())
  }
}

You'll notice a couple new things here: State, Context, and GameResult.

State is all of the data and information required to represent our game's current state. These could be player positions, scores, cards in your hand, etc.. What is included in your state is very dependent on the game you are making.

Context is how ggez gives you access to hardware such as mouse, keyboard, timers, graphics, sound, etc..

GameResult is a utility provided by ggez to signify if there was an error or not. Internally it's just a Result<(), GameError>, which is why we implement EventHandler with GameError, so that on_error knows what to expect. But, we're not going to write any bugs right? 😉

In your main, you will need to create an instance of State.

pub fn main() {
    let state = State {};
}

✔ Check Loop Setup

Test to make sure everything is correct by running cargo run.

You should see this:

warning: unused variable: `state`
  --> src\main.rs:15:9
   |
15 |     let state = &mut State {};
   |         ^^^^^ help: if this is intentional, prefix it with an underscore: `_state`
   |
   = note: `#[warn(unused_variables)]` on by default

warning: unused variable: `ctx`
 --> src\main.rs:6:26
  |
6 |     fn update(&mut self, ctx: &mut Context) -> GameResult {
  |                          ^^^ help: if this is intentional, prefix it with an underscore: `_ctx`

warning: unused variable: `ctx`
 --> src\main.rs:9:24
  |
9 |     fn draw(&mut self, ctx: &mut Context) -> GameResult {
  |                        ^^^ help: if this is intentional, prefix it with an underscore: `_ctx`

And then nothing should happen after it runs. If you saw the warnings and nothing happened, you can continue.

Context

Although we have created a loop, we haven't actually started using it yet. Also, don't mind the loop does nothing right now. We'll get to that soon.

Now is the time for us to interface with our hardware and do something fun. To do that, you need to create a Context courtesy of ggez.

Add this to the end of your main fn:

let c = conf::Conf::new();
let (ctx, event_loop) = ContextBuilder::new("hello_ggez", "awesome_person")
    .default_conf(c)
    .build()
    .unwrap();

This will create a Context with the game_id hello_ggez and the author awesome_person. It will also create an EventsLoop. We'll need it in a minute to call run. Feel free to replace the author with yourself. You are awesome after all.

Now you're ready to kick off the loop!

event::run(ctx, event_loop, state);

✔ Check Context

Once again run cargo run

You should get 2 warnings:

warning: unused variable: `ctx`
 --> src\main.rs:6:26
  |
6 |     fn update(&mut self, ctx: &mut Context) -> GameResult {
  |                          ^^^ help: if this is intentional, prefix it with an underscore: `_ctx`
  |
  = note: `#[warn(unused_variables)]` on by default

warning: unused variable: `ctx`
 --> src\main.rs:9:24
  |
9 |     fn draw(&mut self, ctx: &mut Context) -> GameResult {
  |                        ^^^ help: if this is intentional, prefix it with an underscore: `_ctx`

And a window will pop-up. Hit escape or click the close button to quit.

If you saw the 2 warnings and the window, you're good to continue!

Use the Loop Luke

Alright! We're ready! Let's use the loop with the context!

For this program, we want to display the duration of each frame in the console along with the text "Hello ggez!".

How should we do that? Well, let's look at the 2 callbacks we have in our loop and our State struct.

There is some information we want to track, so we'll modify State first.

struct State {
    dt: std::time::Duration,
}

dt is going to represent the time each frame has taken. It stands for "delta time" and is a useful metric for games to handle variable frame rates.

Now in main, you need to update the State instantiation to include dt:

let state = State {
    dt: std::time::Duration::new(0, 0),
};

So now that we have state to update, let's update it in our update callback! We'll use timer::delta to get the delta time.

fn update(&mut self, ctx: &mut Context) -> GameResult {
    self.dt = timer::delta(ctx);
    Ok(())
}

To see the changes in State, you need to modify the draw callback.

fn draw(&mut self, ctx: &mut Context) -> GameResult {
    println!("Hello ggez! dt = {}ns", self.dt.as_nanos());
    Ok(())
}

Every frame, print out Hello ggez! dt = {}ns. This will print once a frame. Which is going to be a lot.

✔ Check Program

And yet again, run cargo run. A window should pop up and your console should be spammed with "Hello ggez!" and dt's in nanoseconds.

If you see that. Congrats! 🎉 You've successfully bootstrapped a ggez program.

💪 Challenges

If you are looking to push yourself a bit further on your own, these challenges are for you.

Display the time in milliseconds or seconds instead of nanoseconds
Change the size or title of the window that appears
Print the text to the window instead of the console
Limit the framerate to 30fps
Use another callback on EventHandler to do something fun