Type mismatch in example

[janhohenheim]

Im trying to learn how to use the crate by following the collision pipeline example.

However, the following line, as it appears in the example, seems to no longer compile:

// Integrate the positions.
ball_pos = ball_object.position.append_translation(&(timestep * ball_velocity.get()));

Fails with

note: expected type `&nalgebra::TranslationBase<f32, nalgebra::U2, nalgebra::MatrixArray<f32, nalgebra::U2, nalgebra::U1>>`
         found type `&nalgebra::Matrix<f32, nalgebra::U2, nalgebra::U1, nalgebra::MatrixArray<f32, nalgebra::U2, nalgebra::U1>>`

Does anyone know how to fix this?

[sebcrozet]

The documentation seems to be out-of-date. This should be:

ball_pos = ball_object.position.append_translation(&Translation::from_vector(timestep * ball_velocity.get()));

[janhohenheim]

Thank you very much :)
It compiled after using your code with an extra unwrap, as from_vector returns an Option.
Now I've got a runtime error five lines above it:

// Integrate the velocities.
let ball_object   = world.collision_object(8).unwrap();

panics as it's unwrapping None.

Any idea what that might be?

[sebcrozet]

Did you keep the following line fom the example ?

// Add the ball to the world.
world.deferred_add(8, ball_pos, ball, ball_groups, GeometricQueryType::Contacts(0.0), ball_data);

ncollide identifies objects with user-supplied integers. world.collision_object(8) returning None means that no object whith the ID 8 has been added before.

[janhohenheim]

Yup, got it exactly as is. The other identifiers return None as well.

This is my entire code, but apart from the Translation::from_vector and the extern crate uses it's just copy pasted from the example.

[janhohenheim]

I found the problem!
It works if right after

// Add the ball to the world.
world.deferred_add(8, ball_pos, ball, ball_groups, GeometricQueryType::Contacts(0.0), ball_data);

we use

world.update()

Although I have to ask if this behavior is intentional or a bug.