mlt_core/convert/mvt/
encode.rs

1//! Encode layers as MVT (Mapbox Vector Tile) bytes
2
3use std::borrow::Borrow;
4
5use fast_mvt::{MvtTileBuilder, MvtValueRef};
6
7use crate::encoder::LayerSource;
8use crate::tile::TileLayer;
9use crate::{MltError, MltResult, PropValueRef};
10
11/// Encode row-oriented [`TileLayer`]s as MVT (Mapbox Vector Tile) bytes.
12pub fn tile_layers_to_mvt(
13    layers: impl IntoIterator<Item = impl Borrow<TileLayer>>,
14) -> MltResult<Vec<u8>> {
15    let mut tile = MvtTileBuilder::new();
16    for layer in layers {
17        tile = write_mvt_layer(layer.borrow(), tile)?;
18    }
19    Ok(tile.encode())
20}
21
22/// Adds `source` to `tile`, writing each feature straight from the source.
23pub(crate) fn write_mvt_layer(
24    source: &impl LayerSource,
25    tile: MvtTileBuilder,
26) -> MltResult<MvtTileBuilder> {
27    if source.name().is_empty() {
28        return Err(MltError::MissingLayerName);
29    }
30    let mut layer = tile.layer(source.name())?;
31    layer.extent(source.extent().into());
32    for feature in 0..source.feature_count() {
33        let mut out = source.mvt_feature(feature, layer)?;
34        out.id(source.id(feature));
35        for column in 0..source.property_count() {
36            if let Some(value) = source.property(feature, column) {
37                out.tag_ref(source.property_name(column), value.into())?;
38            }
39        }
40        layer = out.end();
41    }
42    Ok(layer.end())
43}
44
45impl<'a> From<PropValueRef<'a>> for MvtValueRef<'a> {
46    fn from(value: PropValueRef<'a>) -> Self {
47        match value {
48            PropValueRef::Bool(v) => Self::Bool(v),
49            PropValueRef::I8(v) => Self::SInt(v.into()),
50            PropValueRef::U8(v) => Self::UInt(v.into()),
51            PropValueRef::I32(v) => Self::SInt(v.into()),
52            PropValueRef::U32(v) => Self::UInt(v.into()),
53            PropValueRef::I64(v) => Self::SInt(v),
54            PropValueRef::U64(v) => Self::UInt(v),
55            PropValueRef::F32(v) => Self::Float(v),
56            PropValueRef::F64(v) => Self::Double(v),
57            PropValueRef::Str(v) => Self::String(v),
58        }
59    }
60}
61
62#[cfg(test)]
63mod tests {
64    use super::*;
65    use crate::mvt::mvt_to_tile_layers;
66    use crate::tile::{Extent, TileFeature};
67
68    #[test]
69    fn empty_input_yields_empty_output() {
70        let bytes = tile_layers_to_mvt(Vec::<TileLayer>::new()).unwrap();
71        let decoded = mvt_to_tile_layers(bytes).unwrap();
72        assert_eq!(decoded, [] as [TileLayer; 0]);
73    }
74
75    #[test]
76    fn rejects_empty_layer_name() {
77        let layer = TileLayer {
78            name: String::new(),
79            extent: Extent::new(4096).unwrap(),
80            property_names: vec![],
81            property_kinds: vec![],
82            #[cfg(feature = "unstable-v2")]
83            m_value_names: vec![],
84            #[cfg(feature = "unstable-v2")]
85            m_value_kinds: vec![],
86            #[cfg(feature = "unstable-v2")]
87            nested_names: vec![],
88            #[cfg(feature = "unstable-v2")]
89            nested_kinds: vec![],
90            #[cfg(feature = "unstable-v2")]
91            z_step: None,
92            features: vec![],
93        };
94
95        assert!(matches!(
96            tile_layers_to_mvt(vec![layer]),
97            Err(MltError::MissingLayerName)
98        ));
99    }
100
101    /// `ClosePath` repeats the first vertex; an input with the closing
102    /// duplicate must therefore round-trip without growing extra vertices.
103    #[test]
104    fn ring_is_implicitly_closed() {
105        use geo_types::{Geometry, LineString, Polygon};
106        let ring = vec![
107            (0_i32, 0_i32).into(),
108            (10, 0).into(),
109            (10, 10).into(),
110            (0, 10).into(),
111            (0, 0).into(),
112        ];
113        let layer = TileLayer::from_parts(
114            "L",
115            4096,
116            vec![],
117            vec![TileFeature {
118                id: Some(1),
119                geometry: Geometry::Polygon(Polygon::new(LineString(ring), vec![])),
120                properties: vec![],
121                #[cfg(feature = "unstable-v2")]
122                m_values: vec![],
123                #[cfg(feature = "unstable-v2")]
124                nested: vec![],
125                #[cfg(feature = "unstable-v2")]
126                z: Vec::new(),
127            }],
128        )
129        .unwrap();
130        let bytes = tile_layers_to_mvt(vec![layer]).unwrap();
131        let back = mvt_to_tile_layers(bytes).unwrap();
132        let Geometry::Polygon(p) = back[0].features()[0].geometry() else {
133            panic!(
134                "expected polygon, got {:?}",
135                back[0].features()[0].geometry()
136            );
137        };
138        assert_eq!(p.exterior().0.len(), 5);
139        assert_eq!(p.exterior().0.first(), p.exterior().0.last());
140    }
141}
mlt_core/convert/mvt/encode.rs

mlt_core/convert/mvt/
encode.rs
