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Change breakout to use fixed timestamp (#1541)

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This PR fixes https://github.com/bevyengine/bevy/issues/1240, where the ball is escaping the playing field at low framerates.  I did this by moving the movement and physics system into a Fixed Timestep system set and changing the movement steps to a constant.  So we lose the example use of delta_time for changing position, but gain a use of FixedTimestep.

If this is accepted https://github.com/bevyengine/bevy-website/pull/102 will need to be updated to match.

Co-authored-by: Carter Anderson <mcanders1@gmail.com>
This commit is contained in:
Mike 2021-04-12 19:29:08 +00:00
parent 60f286d56d
commit 9186c4c8d2
1 changed files with 12 additions and 10 deletions
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22
examples/game/breakout.rs
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@ -1,19 +1,25 @@
use bevy::{
core::FixedTimestep,
prelude::*,
render::pass::ClearColor,
sprite::collide_aabb::{collide, Collision},
};
/// An implementation of the classic game "Breakout"
const TIME_STEP: f32 = 1.0 / 60.0;
fn main() {
App::build()
.add_plugins(DefaultPlugins)
.insert_resource(Scoreboard { score: 0 })
.insert_resource(ClearColor(Color::rgb(0.9, 0.9, 0.9)))
.add_startup_system(setup.system())
.add_system(paddle_movement_system.system())
.add_system(ball_collision_system.system())
.add_system(ball_movement_system.system())
.add_system_set(
SystemSet::new()
.with_run_criteria(FixedTimestep::step(TIME_STEP as f64))
.with_system(paddle_movement_system.system())
.with_system(ball_collision_system.system())
.with_system(ball_movement_system.system()),
)
.add_system(scoreboard_system.system())
.run();
}
@ -175,7 +181,6 @@ fn setup(
}
fn paddle_movement_system(
time: Res<Time>,
keyboard_input: Res<Input<KeyCode>>,
mut query: Query<(&Paddle, &mut Transform)>,
) {
@ -191,18 +196,15 @@ fn paddle_movement_system(
let translation = &mut transform.translation;
// move the paddle horizontally
translation.x += time.delta_seconds() * direction * paddle.speed;
translation.x += direction * paddle.speed * TIME_STEP;
// bound the paddle within the walls
translation.x = translation.x.min(380.0).max(-380.0);
}
}
fn ball_movement_system(time: Res<Time>, mut ball_query: Query<(&Ball, &mut Transform)>) {
// clamp the timestep to stop the ball from escaping when the game starts
let delta_seconds = f32::min(0.2, time.delta_seconds());
fn ball_movement_system(mut ball_query: Query<(&Ball, &mut Transform)>) {
if let Ok((ball, mut transform)) = ball_query.single_mut() {
transform.translation += ball.velocity * delta_seconds;
transform.translation += ball.velocity * TIME_STEP;
}
}