mlt_core/convert/mvt/
encode.rs

1//! Encode row-oriented [`TileLayer`]s as MVT (Mapbox Vector Tile) bytes,
2//! delegating wire-format details to the [`fast_mvt`] crate.
3
4use fast_mvt::{MvtTileBuilder, MvtValue};
5
6use crate::decoder::{PropValue, TileLayer};
7use crate::{MltError, MltResult};
8
9/// Encode row-oriented [`TileLayer`]s as MVT (Mapbox Vector Tile) bytes.
10pub fn tile_layers_to_mvt(layers: Vec<TileLayer>) -> MltResult<Vec<u8>> {
11    let mut tile = MvtTileBuilder::with_capacity(layers.len());
12    for layer in layers {
13        if layer.name.is_empty() {
14            return Err(MltError::MissingLayerName);
15        }
16        let mut mvt_layer = tile.layer_with_capacity(layer.name, layer.features.len())?;
17        mvt_layer.extent(layer.extent.into());
18        for feat in layer.features {
19            let mut feature = mvt_layer.feature(&feat.geometry)?;
20            feature.id(feat.id);
21            for (col_idx, prop) in feat.properties.into_iter().enumerate() {
22                if let Some(name) = layer.property_names.get(col_idx)
23                    && let Ok(value) = MvtValue::try_from(prop)
24                {
25                    feature.tag(name, value)?;
26                }
27            }
28            mvt_layer = feature.finish();
29        }
30        tile = mvt_layer.finish();
31    }
32    Ok(tile.finish())
33}
34
35impl TryFrom<PropValue> for MvtValue {
36    type Error = ();
37
38    fn try_from(prop: PropValue) -> Result<Self, Self::Error> {
39        Ok(match prop {
40            PropValue::Bool(Some(b)) => Self::Bool(b),
41            PropValue::I8(Some(i)) => Self::SInt(i.into()),
42            PropValue::U8(Some(u)) => Self::UInt(u.into()),
43            PropValue::I32(Some(i)) => Self::SInt(i.into()),
44            PropValue::U32(Some(u)) => Self::UInt(u.into()),
45            PropValue::I64(Some(i)) => Self::SInt(i),
46            PropValue::U64(Some(u)) => Self::UInt(u),
47            PropValue::F32(Some(f)) => Self::Float(f),
48            PropValue::F64(Some(f)) => Self::Double(f),
49            PropValue::Str(Some(s)) => Self::String(s),
50            _ => Err(())?,
51        })
52    }
53}
54
55#[cfg(test)]
56mod tests {
57    use super::*;
58    use crate::decoder::{Extent, TileFeature};
59    use crate::mvt::mvt_to_tile_layers;
60
61    #[test]
62    fn empty_input_yields_empty_output() {
63        let bytes = tile_layers_to_mvt(Vec::new()).unwrap();
64        let decoded = mvt_to_tile_layers(bytes).unwrap();
65        assert!(decoded.is_empty());
66    }
67
68    #[test]
69    fn rejects_empty_layer_name() {
70        let layer = TileLayer {
71            name: String::new(),
72            extent: Extent::new(4096).unwrap(),
73            property_names: vec![],
74            property_kinds: vec![],
75            features: vec![],
76        };
77
78        assert!(matches!(
79            tile_layers_to_mvt(vec![layer]),
80            Err(MltError::MissingLayerName)
81        ));
82    }
83
84    /// `ClosePath` repeats the first vertex; an input with the closing
85    /// duplicate must therefore round-trip without growing extra vertices.
86    #[test]
87    fn ring_is_implicitly_closed() {
88        use geo_types::{Geometry, LineString, Polygon};
89        let ring = vec![
90            (0_i32, 0_i32).into(),
91            (10, 0).into(),
92            (10, 10).into(),
93            (0, 10).into(),
94            (0, 0).into(),
95        ];
96        let layer = TileLayer::from_parts(
97            "L",
98            4096,
99            vec![],
100            vec![TileFeature {
101                id: Some(1),
102                geometry: Geometry::Polygon(Polygon::new(LineString(ring), vec![])),
103                properties: vec![],
104            }],
105        )
106        .unwrap();
107        let bytes = tile_layers_to_mvt(vec![layer]).unwrap();
108        let back = mvt_to_tile_layers(bytes).unwrap();
109        let Geometry::Polygon(p) = back[0].features()[0].geometry() else {
110            panic!(
111                "expected polygon, got {:?}",
112                back[0].features()[0].geometry()
113            );
114        };
115        assert_eq!(p.exterior().0.len(), 5);
116        assert_eq!(p.exterior().0.first(), p.exterior().0.last());
117    }
118}
mlt_core/convert/mvt/encode.rs

mlt_core/convert/mvt/
encode.rs
