mapbox · SnailBones · Apr 6, 2022 · Apr 6, 2022 · Apr 6, 2022
diff --git a/debug/custom-source.html b/debug/custom-source.html
@@ -8,54 +8,88 @@
     <style>
         body { margin: 0; padding: 0; }
         html, body, #map { height: 100%; }
+        #controls { position: absolute; top: 0; left: 0; }
     </style>
 </head>
 
 <body>
 <div id='map'></div>
+<div id='controls'>
+    <input id="slider" type="range" list="colors" min="0" step="1">
+    <datalist id="colors"></datalist>
+</div>
 
 <script src='../dist/mapbox-gl-dev.js'></script>
 <script src='../debug/access_token_generated.js'></script>
 <script>
 
 var map = window.map = new mapboxgl.Map({
     container: 'map',
-    center: [-74.5, 40],
-    zoom: 2,
-    style: {
-        version: 8,
-        sources: {},
-        layers: []
-    },
+    center: [0, 0],
+    zoom: 0,
+    style: 'mapbox://styles/mapbox/light-v10',
     hash: true
 });
 
+const tileSize = 256;
+const colors = ['#74a9cf', '#3690c0', '#0570b0', '#045a8d'];
+let currentColor = colors[0];
+
 map.on('load', () => {
     map.addSource('custom-source', {
         type: 'custom',
-        tileSize: 256,
-        attribution: 'Map tiles by <a target="_top" rel="noopener" href="http://stamen.com">Stamen Design</a>, under <a target="_top" rel="noopener" href="http://creativecommons.org/licenses/by/3.0">CC BY 3.0</a>. Data by <a target="_top" rel="noopener" href="http://openstreetmap.org">OpenStreetMap</a>, under <a target="_top" rel="noopener" href="http://creativecommons.org/licenses/by-sa/3.0">CC BY SA</a>',
-        async loadTile(tile, {signal}) {
-            const tilesUrl = 'https://stamen-tiles.a.ssl.fastly.net/watercolor/{z}/{x}/{y}.jpg';
-            const url = tilesUrl
-                .replace('{z}', String(tile.z))
-                .replace('{x}', String(tile.x))
-                .replace('{y}', String(tile.y));
+        tileSize,
+        async loadTile({z, x, y}) {
+            const tileSize = 256;
+            const offscreenCanvas = new OffscreenCanvas(tileSize, tileSize);
+            const context = offscreenCanvas.getContext('2d');
+            context.fillStyle = 'red';
+            context.fillRect(0, 0, tileSize, tileSize);
+
+            context.font = '18px serif';
+            context.fillStyle = 'white';
+            context.textAlign = 'center';
+            context.fillText(`${z}/${x}/${y}`, tileSize / 2, tileSize / 2, tileSize);
 
-            const response = await fetch(url, {signal});
-            const data = await response.arrayBuffer();
+            const imageData = context.getImageData(0, 0, tileSize, tileSize);
+            return imageData;
+        },
+        prepareTile({z, x, y}) {
+            const tileSize = 256;
+            const offscreenCanvas = new OffscreenCanvas(tileSize, tileSize);
+            const context = offscreenCanvas.getContext('2d');
+            context.fillStyle = currentColor;
+            context.fillRect(0, 0, tileSize, tileSize);
 
-            const blob = new window.Blob([new Uint8Array(data)], {type: 'image/png'});
-            const imageBitmap = await window.createImageBitmap(blob);
+            context.font = '18px serif';
+            context.fillStyle = 'white';
+            context.textAlign = 'center';
+            context.fillText(`${z}/${x}/${y}`, tileSize / 2, tileSize / 2, tileSize);
 
-            return imageBitmap;
+            const imageData = context.getImageData(0, 0, tileSize, tileSize);
+            return imageData;
+        },
+        hasTile({z, x, y}) {
+            return (x + y) % 2 === 0;
         }
     });
 
     map.addLayer({
         id: 'custom-source',
         type: 'raster',
-        source: 'custom-source'
+        source: 'custom-source',
+        paint: {
+            'raster-opacity': 0.75,
+            'raster-fade-duration': 0
+        }
+    });
+
+    const slider = document.getElementById('slider');
+    slider.value = 0;
+    slider.max = colors.length - 1;
+    slider.addEventListener('input', (e) => {
+        currentColor = colors[e.target.value];
+        map.triggerRepaint();
     });
 });
 

diff --git a/src/source/custom_source.js b/src/source/custom_source.js
@@ -326,6 +326,7 @@ class CustomSource<T> extends Evented implements Source {
         if (!data) return null;
 
         this.loadTileData(tile, data);
+        tile.state = 'loaded';
         return data;
     }
 

diff --git a/test/release/custom-source.html b/test/release/custom-source.html
@@ -0,0 +1 @@
+../../debug/custom-source.html
diff --git a/test/release/index.js b/test/release/index.js
@@ -101,6 +101,11 @@ const pages = [
         "key": "preload-tiles",
         "title": "Preload tiles",
         "url": "./preload-tiles.html"
+    },
+    {
+        "key": "custom-source",
+        "title": "Custom Source",
+        "url": "./custom-source.html"
     }
 ];
 

diff --git a/test/unit/source/custom_source.test.js b/test/unit/source/custom_source.test.js
@@ -202,6 +202,27 @@ test('CustomSource', (t) => {
         sourceCache._addTile(tileID);
     });
 
+    t.test('loadTile is not called if prepareTile returns data', (t) => {
+        const tileID = new OverscaledTileID(0, 0, 0, 0, 0);
+
+        const loadTile = t.spy();
+        const prepareTile = t.spy((tile) => {
+            const {x, y, z} = tileID.canonical;
+            t.deepEqual(tile, {x, y, z});
+            return new window.ImageData(512, 512);
+        });
+
+        const {sourceCache} = createSource(t, {loadTile, prepareTile});
+
+        sourceCache.onAdd();
+        sourceCache._addTile(tileID);
+
+        t.ok(prepareTile.calledOnce, 'prepareTile must be called');
+        t.notOk(loadTile.calledOnce, 'loadTile must not be called');
+        t.equal(sourceCache._tiles[tileID.key].state, 'loaded', 'tile must be in the loaded state');
+        t.end();
+    });
+
     t.test('prepareTile updates the tile data if it returns valid tile data', (t) => {
         const tileID = new OverscaledTileID(0, 0, 0, 0, 0);