reduce data exchanges across boundary

gpx-rs/wasm/src/lib.rs

@@ -14,7 +14,7 @@ use std::cell::RefCell;
 use wasm_bindgen::prelude::*;
 
 use gpx_engine::{self as engine, Action, Command, Engine, FileId, LngLat, LngLatBounds};
-use js_sys::{Array, BigInt64Array, Float64Array, Object, Reflect, Uint8Array};
+use js_sys::{Array, BigInt64Array, Float64Array, Object, Reflect, Uint8Array, Uint32Array};
 
 #[wasm_bindgen]
 #[derive(Clone, Copy)]
@@ -146,32 +146,63 @@ stats_getter!(lng, Float64Array);
 stats_getter!(lat, Float64Array);
 stats_getter!(ele, Float64Array);
 
-/// Timestamps in milliseconds since the epoch (`NO_TIME`, the smallest i64, when missing).
-#[wasm_bindgen]
-pub fn timestamps() -> BigInt64Array {
-    with_stats(|s| unsafe { BigInt64Array::view(&s.time) })
-        .unwrap_or_else(|| BigInt64Array::new_with_length(0))
+// The optional values are `undefined` when no trackpoint of the selection has one, else they have
+// an entry per trackpoint, the missing ones being NaN (`NO_TIME` for the timestamps).
+macro_rules! optional_stats_getter {
+    ($name:ident, $field:ident, $array:ident) => {
+        #[wasm_bindgen]
+        pub fn $name() -> Option<$array> {
+            with_stats(|s| {
+                s.$field
+                    .as_ref()
+                    .map(|values| unsafe { $array::view(values) })
+            })
+            .flatten()
+        }
+    };
 }
 
+// Timestamps in milliseconds since the epoch (`NO_TIME`, the smallest i64, when missing).
+optional_stats_getter!(timestamps, time, BigInt64Array);
+
 /// Value of the timestamps of the trackpoints that have none.
 #[wasm_bindgen]
 pub fn no_time() -> i64 {
     engine::NO_TIME
 }
 
-stats_getter!(hr, Float64Array);
-stats_getter!(cad, Float64Array);
-stats_getter!(atemp, Float64Array);
-stats_getter!(power, Float64Array);
+optional_stats_getter!(hr, hr, Float64Array);
+optional_stats_getter!(cad, cad, Float64Array);
+optional_stats_getter!(atemp, atemp, Float64Array);
+optional_stats_getter!(power, power, Float64Array);
 
-// Surface, highway, SAC scale and MTB scale of the trackpoints: 0 when unknown, else 1 + the index
-// in `surfaces()`, `highways()`, `sac_scales()` or `mtb_scales()`.
-stats_getter!(surface, Uint8Array);
-stats_getter!(highway, Uint8Array);
-stats_getter!(sac_scale, Uint8Array);
-stats_getter!(mtb_scale, Uint8Array);
+// Surface, highway, SAC scale and MTB scale of the trackpoints, as intervals of trackpoints that
+// have the same value: `<name>_starts` holds the index of the first trackpoint of each interval,
+// and `<name>_values` its value (0 when unknown, else 1 + the index in `surfaces()`,
+// `highways()`, `sac_scales()` or `mtb_scales()`). A value that is unknown for every trackpoint is
+// a single interval.
+macro_rules! intervals_getters {
+    ($starts:ident, $values:ident, $field:ident) => {
+        #[wasm_bindgen]
+        pub fn $starts() -> Uint32Array {
+            with_stats(|s| unsafe { Uint32Array::view(&s.$field.starts) })
+                .unwrap_or_else(|| Uint32Array::new_with_length(0))
+        }
 
-/// The names of the surfaces, in the order of their codes (see `surface`). The list only grows:
+        #[wasm_bindgen]
+        pub fn $values() -> Uint8Array {
+            with_stats(|s| unsafe { Uint8Array::view(&s.$field.values) })
+                .unwrap_or_else(|| Uint8Array::new_with_length(0))
+        }
+    };
+}
+
+intervals_getters!(surface_starts, surface_values, surface);
+intervals_getters!(highway_starts, highway_values, highway);
+intervals_getters!(sac_scale_starts, sac_scale_values, sac_scale);
+intervals_getters!(mtb_scale_starts, mtb_scale_values, mtb_scale);
+
+/// The names of the surfaces, in the order of their codes (see `surface_values`). The list only grows:
 /// a name keeps its index.
 #[wasm_bindgen]
 pub fn surfaces() -> StringList {
@@ -180,7 +211,7 @@ pub fn surfaces() -> StringList {
         .unchecked_into()
 }
 
-/// The names of the highways, in the order of their codes (see `highway`).
+/// The names of the highways, in the order of their codes (see `highway_values`).
 #[wasm_bindgen]
 pub fn highways() -> StringList {
     with_engine(|e| array(e.categories().highway.names(), |name| name.as_str().into()))
@@ -188,7 +219,7 @@ pub fn highways() -> StringList {
         .unchecked_into()
 }
 
-/// The names of the SAC scales, in the order of their codes (see `sac_scale`).
+/// The names of the SAC scales, in the order of their codes (see `sac_scale_values`).
 #[wasm_bindgen]
 pub fn sac_scales() -> StringList {
     with_engine(|e| {
@@ -200,7 +231,7 @@ pub fn sac_scales() -> StringList {
     .unchecked_into()
 }
 
-/// The names of the MTB scales, in the order of their codes (see `mtb_scale`).
+/// The names of the MTB scales, in the order of their codes (see `mtb_scale_values`).
 #[wasm_bindgen]
 pub fn mtb_scales() -> StringList {
     with_engine(|e| {