Inaccurate collisions when using a lot of ColliderShapes with the same height

[daxpedda]

When programming a simple platformer, building a straight path out of many ColliderShapes and having a character walk on it doesn't work.

I am assuming that the issue is that the y-coordinate of every ColliderShape is not exactly the same, because of f32 inaccuracies. So the character walks along the straight path but bumps into a block that isn't exactly on the same y-coordinate as the one before it.

Example code

use bevy::prelude::*;
use bevy_rapier2d::prelude::*;

const SCALE: f32 = 16.;
const PLATFORM_Y: f32 = -8.;
const TILES: isize = 100;
const CONTROLLER_JUMP_IMPULSE: f32 = 15.;

fn main() {
  let mut app = App::new();
  app.add_plugins(DefaultPlugins);
  app.add_plugin(RapierRenderPlugin);
  app.add_plugin(RapierPhysicsPlugin::<NoUserData>::default());
  app.add_startup_system(setup)
  	.add_system(movement);

  app.run()
}

#[derive(Component)]
struct Controller;

fn setup(mut commands: Commands, mut rapier_config: ResMut<RapierConfiguration>) {
  commands
  	.spawn()
  	.insert_bundle(OrthographicCameraBundle::new_2d());

  rapier_config.scale = SCALE;

  commands
  	.spawn()
  	.insert_bundle(RigidBodyBundle {
  		mass_properties: RigidBodyMassPropsFlags::ROTATION_LOCKED.into(),
  		..Default::default()
  	})
  	.insert_bundle(SpriteBundle {
  		sprite: Sprite {
  			color: Color::rgb(1., 0., 0.),
  			custom_size: Some(Vec2::new(1. * SCALE, 2. * SCALE)),
  			..Default::default()
  		},
  		..Default::default()
  	})
  	.insert_bundle(ColliderBundle {
  		shape: ColliderShape::cuboid(0.5, 1.).into(),
  		..Default::default()
  	})
  	.insert(ColliderPositionSync::Discrete).insert(Controller);

  for x in -TILES / 2..TILES / 2 {
  	commands
  		.spawn()
  		.insert_bundle(SpriteBundle {
  			sprite: Sprite {
                  color: Color::rgb(0., 1., 0.),
                  custom_size: Some(Vec2::new(1. * SCALE, 1. * SCALE)),
                  ..Default::default()
              },
  			transform: Transform::from_xyz(x as f32 * SCALE, PLATFORM_Y * SCALE, 0.),
  			..Default::default()
  		})
  		.insert_bundle(ColliderBundle {
  			shape: ColliderShape::cuboid(0.5, 0.5).into(),
  			position: [x as f32, PLATFORM_Y].into(),
  			..Default::default()
  		});
  }
}

fn movement(
  keyboard_input: Res<Input<KeyCode>>,
  mut controller: Query<(
  	&mut RigidBodyForcesComponent,
  	&mut RigidBodyVelocityComponent,
  	&RigidBodyMassPropsComponent,
  	&mut ColliderMaterialComponent,
  ), With<Controller>>,
) {
  let (mut rb_forces, mut rb_vel, rb_mprops, mut co_material) = controller.single_mut();

  if keyboard_input.just_pressed(KeyCode::Space) {
  	rb_vel.apply_impulse(rb_mprops, Vec2::new(0., CONTROLLER_JUMP_IMPULSE).into());
  }

  let mut x_axis = 0.;

  if keyboard_input.pressed(KeyCode::A) || keyboard_input.pressed(KeyCode::Left) {
  	x_axis -= 1.;
  } else if keyboard_input.pressed(KeyCode::D) || keyboard_input.pressed(KeyCode::Right) {
  	x_axis += 1.;
  }

  if x_axis == 0. {
  	co_material.friction = 2.;
  } else {
      co_material.friction = 0.;
  	x_axis *= 25. * rb_mprops.mass();
  	rb_forces.force.x = x_axis;
  }
}

Somebody else had this issue before, probably with a better explanation of what the issue is about: https://dev.to/sbelzile/making-games-in-rust-part-7-fixing-the-player-randomly-stuck-issue-3mj5.

[brandon-reinhart]

I've run into this as well, but meshing all of the tiles is probably the right solution anyway. Still annoying that it blocks quick n' dirty tests.

[Vrixyz]

I think that's a rapier issue, but I agree it would be convenient to be able to have a smoother experience for "quick n' dirty tests".

Any update on reproduction code is appreciated.