add Squash The Creeps tutorial #4

FrankCasanova · 2025-03-27T14:59:05Z

squash-the-creeps/rust/src/main_scene.rs

Yarwin · 2025-03-27T15:18:25Z

squash-the-creeps/rust/src/main_scene.rs

+
+#[godot_api]
+impl INode for MainScene {
+    fn init(base: Base<Node>) -> Self {


IMO auto-derrived init (i.e #[class(init, base=Node)] should be preferred

Reasoning – it simplifies all the boilerplate, and allows one to initialize&add new fields without bunch of refactors. It makes easier to spot default values as well

squash-the-creeps/rust/src/main_scene.rs

Yarwin · 2025-03-27T15:20:42Z

squash-the-creeps/rust/src/main_scene.rs

+    fn ready(&mut self) {
+        self.to_gd();
+
+        //$UserInterface/Retry.hide()


Please, add a space between // and actual comment text 😅

squash-the-creeps/rust/src/main_scene.rs

Yarwin · 2025-03-27T15:23:09Z

squash-the-creeps/rust/src/main_scene.rs

+        mob.bind_mut()
+            .initialize(mob_spawn_location.get_position(), player_position);
+        //mob.squashed.connect($UserInterface/ScoreLabel._on_mob_squashed.bind())
+        mob.connect(


we can use typed signals here 🤔.

squash-the-creeps/rust/src/main_scene.rs

squash-the-creeps/rust/src/mob.rs

Yarwin · 2025-03-27T15:24:50Z

squash-the-creeps/rust/src/mob.rs

+#[derive(GodotClass)]
+#[class(base=CharacterBody3D)]
+pub struct Mob {
+    //Minimum speed of the mob in meters per second.
+    min_speed: f32,
+    //Maximum speed of the mob in meters per second.
+    max_speed: f32,
+    base: Base<CharacterBody3D>,
+}


#[derive(GodotClass)] #[class(init, base=CharacterBody3D)] pub struct Mob { /// Minimum speed of the mob in meters per second. #[export] min_speed: f32, /// Maximum speed of the mob in meters per second. #[export] max_speed: f32, base: Base<CharacterBody3D>, }

squash-the-creeps/rust/src/mob.rs

Yarwin · 2025-03-27T15:28:10Z

squash-the-creeps/rust/src/player.rs

+#[derive(GodotClass)]
+#[class(base=CharacterBody3D)]
+pub struct Player {
+    //How fast the player moves in meters per second.
+    speed: f32,
+    //Vertical impulse applied to the character upon jumping in meters per second.
+    jump_impulse: f32,
+    //Vertical impulse applied to the character upon bouncing over a mob in meters per second.
+    bounce_impulse: f32,
+    //The downward acceleration when in the air, in meters per second.
+    fall_acceleration: f32,
+    //The target velocity of the character (node property)
+    target_velocity: Vector3,
+
+    base: Base<CharacterBody3D>,
+}


Suggested change

#[derive(GodotClass)]

#[class(base=CharacterBody3D)]

pub struct Player {

//How fast the player moves in meters per second.

speed: f32,

//Vertical impulse applied to the character upon jumping in meters per second.

jump_impulse: f32,

//Vertical impulse applied to the character upon bouncing over a mob in meters per second.

bounce_impulse: f32,

//The downward acceleration when in the air, in meters per second.

fall_acceleration: f32,

//The target velocity of the character (node property)

target_velocity: Vector3,

base: Base<CharacterBody3D>,

}

#[derive(GodotClass)]

#[class(init, base=CharacterBody3D)]

pub struct Player {

/// How fast the player moves in meters per second.

#[export]

speed: f32,

/// Vertical impulse applied to the character upon jumping in meters per second.

#[export]

jump_impulse: f32,

/// Vertical impulse applied to the character upon bouncing over a mob in meters per second.

#[export]

bounce_impulse: f32,

/// The downward acceleration when in the air, in meters per second.

#[export]

fall_acceleration: f32,

/// The target velocity of the character (node property)

#[export]

target_velocity: Vector3,

base: Base<CharacterBody3D>,

}

squash-the-creeps/rust/src/player.rs

Yarwin · 2025-03-27T15:30:23Z

squash-the-creeps/rust/src/player.rs

+            //var collision = get_slide_collision(index)
+            let collision = self.base_mut().get_slide_collision(index).unwrap();
+            //if collision.get_collider().is_in_group("mob"):
+            if let Some(collider) = collision.get_collider() {


you can use let Some(collider) = collision.get_collider() else { continue }; here (and bellow as well)

squash-the-creeps/rust/README.md

Yarwin · 2025-03-27T15:36:46Z

squash-the-creeps/rust/cheatseet.txt

@@ -0,0 +1,98 @@
+There are some guidelines you can rely on (which you probably already know):


(which you probably already know) doesn't add something here – it is just noise. I would advise to remove it

Shouldn't this file be .md instead of .txt?

squash-the-creeps/rust/cheatseet.txt

Yarwin · 2025-03-27T15:44:15Z

squash-the-creeps/rust/cheatseet.txt

+Both the godot documentation and the gdext-rust bindings specify which are const and which aren't, the gdext bindings specify that through method signatures (eg: fn get_position(&Node2D) vs fn add_child(&mut Node)).
+
+Non-const methods
+Calling can be done with either <&mut MyClass>::base_mut().method() or <&mut Gd<MyClass>::method().


Calling what (built-in, inherited methods)?

I would use snippets instead of mental shortcuts there (and further on), for example:

let mut obj: Gd<MyClass> = MyClass.new_alloc(); // To call method with &self receiver obj.bind().method(); // To call method with &mut self receiver obj.bind_mut().method();

<Type> has some specific meaning in rust, so it is misleading. (it can be used as <T>::method(&mut receiver... args);)

squash-the-creeps/rust/cheatseet.txt

Yarwin · 2025-03-27T15:48:12Z

squash-the-creeps/rust/cheatseet.txt

+Let's analyze this snippet from your player.rs:
+
+```rust
+if let Some(collider) = collision.get_collider() {


I made a comment earlier, but let Some(...) else {continue }; should be preferred in such cases

Yarwin · 2025-03-27T15:49:44Z

squash-the-creeps/rust/src/player.rs

+                if let Some(node) = collider.try_cast::<Node3D>().ok() {
+                    if node.is_in_group("mob") {
+                        //var mob = collision.get_collider()
+                        let mut mob = collision.get_collider().unwrap().cast::<Mob>();


is there a case in which collider can be null 🤔? I would use expect(some reasoning) instead of unwrap here 🤔 .

squash-the-creeps/rust/cheatseet.txt

Yarwin · 2025-03-27T15:54:54Z

I'll give the proper look (and A/B testing with both squash the creeps) tomorrow; in meanwhile make sure to deal with clippy errors https://github.com/godot-rust/demo-projects/actions/runs/14109802627/job/39525244314?pr=4

EDIT: Done, control scheme is weird, gdextension file is wrongly configured, exports are missing (ofc), outside of that it is fine

squash-the-creeps/godot/RustScripts.gdextension

Yarwin · 2025-03-29T08:19:41Z

Also add "squash-the-creeps/rust" to members in our "main" Cargo.toml.

FrankCasanova · 2025-03-30T15:05:09Z

@Yarwin take a look at it when u have time and feel like it

Bromeon

Thanks a lot so far!

I'm not sure if writing the GDScript code on top of each Rust line is helpful. In fact, it becomes distracting pretty quickly; the need to use base() etc. becomes apparent quite faster after the first few times. A translation table / cheatsheet in the book would be more expedient in that regard.

If you absolutely want to do this, then please limit it to cases where GDScript and Rust are vastly different and it's very hard to find out the Rust code from the GDScript one. And please prefix the comment with // GDScript: <code>, so it's clear what it means. But avoid it, whenever reading the Rust code makes obvious how the GDScript code could have looked.

Bromeon · 2025-03-30T15:29:30Z

squash-the-creeps/godot/main.tscn

@@ -131,4 +131,5 @@ grow_horizontal = 2
 grow_vertical = 2
 text = "Press enter retry"

+[connection signal="hit" from="Player" to="." method="on_player_hit"]


Please define all signal connections in Rust code.

Some may still need the "manual" API but it's much easier to migrate that, than some scene files. They're also less brittle -- scene connections tend to be messed up when loading with a wrong Godot version.

thanks a lot for those guidelines, and about this, i dont know if i know how to do it exactly (im noob), but anyway, if i dont know tomorrow ill ask

squash-the-creeps/godot/rust.gdextension

squash-the-creeps/rust/.cargo/cargo.toml

squash-the-creeps/rust/Cargo.toml

Bromeon · 2025-03-30T15:32:21Z

squash-the-creeps/rust/build-wasm.sh

+#!/bin/sh
+# Copyright (c) godot-rust; Bromeon and contributors.
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+# Must be in dodge-the-creep's rust directory in order to pick up the .cargo/config
+cd `dirname "$0"`
+
+# We build the host gdextension first so that the godot editor doesn't complain.
+cargo +nightly build --package dodge-the-creeps &&
+cargo +nightly build --package dodge-the-creeps \
+  --features godot/experimental-wasm,godot/lazy-function-tables \
+  --target wasm32-unknown-emscripten -Zbuild-std $@


This is building the wrong package.

Bromeon · 2025-03-30T15:32:39Z

squash-the-creeps/rust/src/lib.rs

+mod scorelabel;
+use godot::prelude::*;
+
+struct Scripts;


Suggested change

struct Scripts;

struct SquashTheCreeps;

Bromeon · 2025-03-30T15:40:27Z

squash-the-creeps/rust/src/player.rs

+        // We apply gravity every frame so the character always collides with the ground when moving.
+        // This is necessary for the is_on_floor() function to work as a body can always detect
+        // the floor, walls, etc. when a collision happens the same frame.
+        if !self.base().is_on_floor() {
+            // velocity.y -= fall_acceleration * delta
+            self.target_velocity.y -= self.fall_acceleration * _delta as f32;
+        }
+        // moving the Character
+        let velocity = self.target_velocity;
+        self.base_mut().set_velocity(velocity);
+        // move_and_slide()
+        self.base_mut().move_and_slide();


General style guide:

Comments should whenever possible be proper sentences. Even keywords should ideally start with uppercase and end with period.

Separate groups of lines that belong together with an empty line, so they're visually more recognizable.

As mentioned, avoid obvious GDScript comments.

The first comment here is perfect, here's a suggestion for the remaining parts:

Suggested change

// We apply gravity every frame so the character always collides with the ground when moving.

// This is necessary for the is_on_floor() function to work as a body can always detect

// the floor, walls, etc. when a collision happens the same frame.

if !self.base().is_on_floor() {

// velocity.y -= fall_acceleration * delta

self.target_velocity.y -= self.fall_acceleration * _delta as f32;

}

// moving the Character

let velocity = self.target_velocity;

self.base_mut().set_velocity(velocity);

// move_and_slide()

self.base_mut().move_and_slide();

// We apply gravity every frame so the character always collides with the ground when moving.

// This is necessary for the is_on_floor() function to work as a body can always detect

// the floor, walls, etc. when a collision happens the same frame.

if !self.base().is_on_floor() {

// velocity.y -= fall_acceleration * delta

self.target_velocity.y -= self.fall_acceleration * _delta as f32;

}

// Move the character.

let velocity = self.target_velocity;

self.base_mut().set_velocity(velocity);

self.base_mut().move_and_slide();

In this particular case, it's also possible to store base_mut() in a variable, to reuse the guard and avoid repeated locking. Although it's not that important for a basic example.

let base = self.base_mut(); if base.is_on_floor() ... { } ... base.set_velocity() base.move_and_slide()

squash-the-creeps/rust/src/player.rs

squash-the-creeps/rust/src/scorelabel.rs

squash-the-creeps/rust/src/main_scene.rs

squash-the-creeps/rust/src/player.rs

squash-the-creeps/rust/src/scorelabel.rs

squash-the-creeps/rust/Cargo.toml

squash-the-creeps/rust/src/main_scene.rs

Bromeon · 2025-06-14T10:57:22Z

Ci failed on macos-arm with:

libc++abi: Pure virtual function called!
./.github/other/check-example.sh: line 38:  9109 Abort trap: 6           timeout "$EDITOR_TIMEOUT"s "$GODOT4_BIN" -e --headless --path "$dir" --quit
Error: # DEMO hot-reload | Godot editor failed to open in time.
Error: Process completed with exit code 1.

Very likely unrelated to this PR, our nightly CI hit the same error a few days ago. I asked about it on RocketChat, but seems like no one has seen this. I wonder if it's a problem or in Godot -- but it seems to happen only since recently, indicating it's a recent Godot in-dev version.

Retrying might work, but we should probably sooner or later address this properly 🙂

Yarwin · 2025-06-14T17:13:03Z

@Bromeon we encountered it earlier actually: https://github.com/godot-rust/demo-projects/actions/runs/15544817340/job/43763899820 but I discarded it as an artifact of github-related issues 🤔. It seems to be "random".

I don't have an access to MacOS device as well, thus I'm similarly limited when it comes to doing any debugging >:[

Bromeon · 2025-06-14T17:25:48Z

With these issues I'm very hesitant to spend much time debugging. Especially without macOS device, it's a big effort and tiny reward.

Maybe we should just use retry.sh and move on with life... (outside this PR)

TitanNano · 2025-06-14T18:32:50Z

@Bromeon @Yarwin I can take a look at it on my local machine. As I understand, this is something that just sporadically occurs in CI, right?