Add getFonts(). Fixes #26.

README.md

@@ -10,9 +10,10 @@ Major features:
 * All properties can be expressed as camelCase rather than kebab-case.
 * Layer operations can act on multiple layers (given by array, regex or filter function), not just one.
 * Source types, layer types and property names are incorporated into function names: `addGeoJSON()`, `addCircleLayer()`, `setCircleRadius()`...
-* Some other convenience functions: `show()`, `hide()`, `onLoad()`, `setData()`,
+* Adding layers and sources is idempotent: call `addLineLayer()` multiple times to create, then update the layer.
+* Some other convenience functions: `show()`, `hide()`, `onLoad()`, `setData()`, `fontsInUse()`
 * Better click and hover functions: `hoverPointer()`, `hoverFeatureState()`, `hoverPopup()`, `clickLayer()`
-* Some functions behave better: `removeLayer()` (not an error if layer doesn't exist), `removeSource()` (removes attached layers automatically), `setFilter()` (works on multiple layers at once)
+* Some functions behave better: `removeLayer()` (not an error if layer doesn't exist), `removeSource()` (removes attached layers automatically), `setFilter()` (works on multiple layers at once), `setData()` clears data if no GeoJSON provided.
 
 ```js
 // Adds U property to map, containing these methods.
@@ -21,7 +22,6 @@ const U = require('mapbox-gl-utils').init(map);
 // Certain methods (eg hoverPopup) require access to the mapboxgl library itself
 const mapboxgl = require('mapbox-gl');
 const U = require('mapbox-gl-utils').init(map, mapboxgl);
-
 ```
 
 ### Adding and removing layers
@@ -225,6 +225,10 @@ map.U.loadImage('marker', '/assets/marker-pin@2x.png', { pixelRatio: 2}).then(/*
 
 // Update the map style's root "transition" property
 map.U.setTransition({ delay: 1000, delay: 0});
+
+// Get a list of fonts used in symbol layers with fontsUsed(). Useful for quickly getting some text displaying.
+const fonts = map.U.fontsInUse();
+map.U.addSymbolLayer('labels', 'mysource', { textFont: fonts[0], textField: '{label}' });
 ```
 
 ### Contrived example

src/index.js

@@ -603,6 +603,44 @@ Object.assign(Utils.prototype, {
         this.map.touchZoomRotate.disableRotation();
         this.map.dragRotate.disable();
     },
+    fontsInUse() {
+        // TODO add tests
+        // TODO: find fonts burried within ['format', ... { 'text-font': ... }] expressions
+        function findLiterals(expr) {
+            if (Array.isArray(expr)) {
+                if (expr[0] === 'literal') {
+                    ///
+                    fonts.push(...expr[1]);
+                } else {
+                    expr.forEach(findLiterals);
+                }
+            }
+        }
+        let fonts = [];
+        const fontExprs = this.map
+            .getStyle()
+            .layers.map(l => l.layout && l.layout['text-font'])
+            .filter(Boolean);
+        for (const fontExpr of fontExprs) {
+            // if top level expression is an array of strings, it's hopefully ['Arial', ...] and not ['get', 'font']
+            if (fontExpr.stops) {
+                // old-school base/stops
+                // TODO verify we have got all the cases
+                try {
+                    fonts.push(
+                        ...fontExpr.stops.flat().filter(Array.isArray).flat()
+                    );
+                } catch {
+                    console.log("Couldn't process font expression:", fontExpr);
+                }
+            } else if (fontExpr.every(f => typeof f === 'string')) {
+                fonts.push(...fontExpr);
+            } else {
+                findLiterals(fontExpr);
+            }
+        }
+        return [...new Set(fonts)];
+    },
 });
 /* options:
     addLayers: [{ id: ..., ... }, ...]