Hexagon generation seems to not working correctly

[JohnTheCoolingFan]

I'm using generate_hexagon to select tiles that are in range for player to see. But this is what I get:

It's supposed to be just a hexagon, but every other row below the center is shifted!

Here are code snippets of the project:

fn chart_map(
    player: Query<(&MapPos, &ChartRange), With<PlayerVehicle>>,
    mut tiles: Query<(&mut TileVisibility, &TilePos, &TilemapId)>,
    chunks: Query<&Chunk>,
) {
    let (player_pos, chart_range) = player.single();
    let tiles_in_chart_range: Vec<RowEvenPos> =
        generate_hexagon(player_pos.pos.into(), chart_range.0)
            .into_iter()
            .map(Into::into)
            .collect();
    for (mut tile_vis, tile_pos, tilemap_id) in tiles.iter_mut() {
        let chunk = chunks.get(tilemap_id.0).unwrap();
        let global_tile_pos = global_from_chunk_and_local(chunk.pos, *tile_pos);
        if tiles_in_chart_range.contains(&global_tile_pos) {
            *tile_vis = TileVisibility::Visible
        } else if matches!(*tile_vis, TileVisibility::Visible) {
            *tile_vis = TileVisibility::Charted
        }
    }
}

pub fn global_from_chunk_and_local(chunk: IVec2, local: TilePos) -> RowEvenPos {
    RowEvenPos {
        q: chunk.x * TILEMAP_CHUNK_SIZE.x as i32 + local.x as i32,
        r: chunk.y * TILEMAP_CHUNK_SIZE.y as i32 + local.y as i32,
    }
}

And also the project is on github: https://github.com/JohnTheCoolingFan/sands_of_merkhyl/tree/b69881fde365a79716ed8cb02999443350f8a832

[rparrett]

I think this is a bug with:

bevy_ecs_tilemap/src/helpers/hex_grid/axial.rs

Line 125 in d2740a4

impl From<AxialPos> for RowEvenPos {

And possibly other coordinate conversions. (Needs further investigation)

If I replace that conversion with

impl From<AxialPos> for RowEvenPos {
    fn from(axial_pos: AxialPos) -> Self {
        let AxialPos { q, r } = axial_pos;

        RowEvenPos {
            q: q + (r + (r & 1)) / 2,
            r,
        }
    }
}

(see https://www.redblobgames.com/grids/hexagons/#conversions-offset)

then your map seems to render correctly.

[JohnTheCoolingFan]

Then this makes me think, maybe there's also problems with other AxialPos related conversions? This would probably need further testing, currently thinking on how to set it up.

[rparrett]

Yeah, I think they are all suspect. Especially anything using ceiled_division_by_2, which seems obviously wrong to me.

I think maybe we aren't seeing this in the hex_neighbors example because there are aren't any negative q coordinates there?

It would be great if we could rework that example so that we can repro there.

[JohnTheCoolingFan]

hex_neighbors example doesn't use this at all, it just HexNeighbors struct, which doesn't output AxialPos, but TilePos instead and can't handle tiles that are not on the map. So maybe this case requires additional example?

[rparrett]

Just adding some actual rust tests for those conversion functions would probably be better.

I'm personally more inclined to remove/simplify existing hex examples actually.

[JohnTheCoolingFan]

IMO some of these examples show some important details of hex tilemap. Besides, I think it's easier to verify the system visually than figuring out valid coordinates, especially with hex. Although it is more robust and cheaper in developer time.