How to render 3D points and lines?

[carlbean]

Hi there,

What would be the best (simplest) way to render 3d points and lines? Like point clouds and wireframes.
I'm looking for something like ImmediateGeometry in Godot.

Thanks in advance!

---

Update:

I managed to draw lines with Mesh::new(PrimitiveTopology::LineStrip) 🤩
Unfortunately, i don't get visible results with PrimitiveTopology::PointList.
Also, i cant figure it out how to set line width and point size. Is there a material that can help with that?

Example:

use bevy::prelude::*;

fn main() {
    App::build()
        .insert_resource(Msaa { samples: 4 })
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .run();
}

/// set up a simple 3D scene
fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    let vertices = [
        ([0.0, 0.0, 0.0], [0.0, 1.0, 0.0], [1.0, 1.0]),
        ([1.0, 2.0, 1.0], [0.0, 1.0, 0.0], [1.0, 1.0]),
        ([2.0, 0.0, 0.0], [0.0, 1.0, 0.0], [1.0, 1.0]),
    ];

    let indices = bevy::render::mesh::Indices::U32(vec![0, 2, 1, 0, 3, 2]);

    let mut positions = Vec::new();
    let mut normals = Vec::new();
    let mut uvs = Vec::new();
    for (position, normal, uv) in vertices.iter() {
        positions.push(*position);
        normals.push(*normal);
        uvs.push(*uv);
    }

    let mut mesh = Mesh::new(bevy::render::pipeline::PrimitiveTopology::LineStrip);
    mesh.set_indices(Some(indices));
    mesh.set_attribute(Mesh::ATTRIBUTE_POSITION, positions);
    mesh.set_attribute(Mesh::ATTRIBUTE_NORMAL, normals);
    mesh.set_attribute(Mesh::ATTRIBUTE_UV_0, uvs);

    // add entities to the world
    // plane
    commands.spawn_bundle(PbrBundle {
        mesh: meshes.add(mesh),
        material: materials.add(Color::rgb(0.3, 0.5, 0.3).into()),
        ..Default::default()
    });
    // light
    commands.spawn_bundle(LightBundle {
        transform: Transform::from_translation(Vec3::new(4.0, 8.0, 4.0)),
        ..Default::default()
    });
    // camera
    commands.spawn_bundle(PerspectiveCameraBundle {
        transform: Transform::from_translation(Vec3::new(-2.0, 2.5, 5.0))
            .looking_at(Vec3::default(), Vec3::unit_y()),
        ..Default::default()
    });
}

based on: https://stackoverflow.com/a/66724123/3615288

[VVishion]

Unfortunatelly, you can't set line width and point size. Thats because you are using the graphics api with a thin layer here which does not support this approach. Setting width for something can't be a material, because a material typically does not alter the mesh.
But you can draw a stretched quad. A quad and its mesh are already implemented in bevy (Mesh::from(mesh::shape::Quad)). Just scale it to your needs. Now you can have a line with width. A thicker point can be also be achieved with triangles or any approximation.
Im not familiar with PointList.

[carlbean]

Thank you for the reply!

I was hoping to achieve something like SpatialMaterail does in Godot. (It just has point_size and line_width as a setting)

I guess i'll have to create a custom material for that. Since i don't know much about shaders, if anyone knows some examples to get me started i'd really appreciate it 🙏

[mtsr]

You can also look at how I approached line drawing in https://github.com/ForesightMiningSoftwareCorporation/bevy_polyline