Add a region growing example

Makefile

@@ -19,7 +19,7 @@ BUILD_HOSTED := build/hosted/$(BRANCH)
 BUILD_HOSTED_EXAMPLES := $(addprefix $(BUILD_HOSTED)/,$(EXAMPLES))
 BUILD_HOSTED_EXAMPLES_JS := $(addprefix $(BUILD_HOSTED)/,$(EXAMPLES_JS))
 
-UNPHANTOMABLE_EXAMPLES = examples/shaded-relief.html examples/raster.html
+UNPHANTOMABLE_EXAMPLES = examples/shaded-relief.html examples/raster.html examples/region-growing.html
 CHECK_EXAMPLE_TIMESTAMPS = $(patsubst examples/%.html,build/timestamps/check-%-timestamp,$(filter-out $(UNPHANTOMABLE_EXAMPLES),$(EXAMPLES_HTML)))
 
 TASKS_JS := $(shell find tasks -name '*.js')

examples/region-growing.html

@@ -0,0 +1,43 @@
+---
+template: example.html
+title: Region Growing
+shortdesc: Grow a region from a seed pixel
+docs: >
+  <p>Click a region on the map. The computed region will be red.</p>
+  <p>
+    This example uses a <code>ol.source.Raster</code> to generate data
+    based on another source.  The raster source accepts any number of
+    input sources (tile or image based) and runs a pipeline of
+    operations on the input data.  The return from the final
+    operation is used as the data for the output source.
+  </p>
+  <p>
+    In this case, a single tiled source of imagery data is used as input.
+    The region is calculated in a single "image" operation using the "seed"
+    pixel provided by the user clicking on the map. The "threshold" value
+    determines whether a given contiguous pixel belongs to the "region" - the
+    difference between a candidate pixel's RGB values and the seed values must
+    be below the threshold.
+  </p>
+  <p>
+    This example also shows how an additional function can be made available
+    to the operation.
+  </p>
+tags: "raster, region growing"
+---
+<div class="row-fluid">
+  <div class="span12">
+    <div id="map" class="map"></div>
+  </div>
+</div>
+<div class="row">
+  <div class="col-md-1">
+    Threshold:
+  </div>
+  <div class="col-md-2">
+    <input id="threshold" type="range" min="1" max="50" value="20"/>
+  </div>
+  <div class="col-md-1">
+    <span id="threshold-value"></span>
+  </div>
+</div>

examples/region-growing.js

@@ -0,0 +1,134 @@
+// NOCOMPILE
+goog.require('ol.Map');
+goog.require('ol.View');
+goog.require('ol.layer.Image');
+goog.require('ol.layer.Tile');
+goog.require('ol.proj');
+goog.require('ol.source.BingMaps');
+goog.require('ol.source.Raster');
+
+function growRegion(inputs, data) {
+  var image = inputs[0];
+  var seed = data.pixel;
+  var delta = parseInt(data.delta);
+  if (!seed) {
+    return [image];
+  }
+
+  seed = seed.map(Math.round);
+  var width = image.width;
+  var height = image.height;
+  var inputData = image.data;
+  var outputData = new Uint8ClampedArray(inputData);
+  var seedIdx = (seed[1] * width + seed[0]) * 4;
+  var seedR = inputData[seedIdx];
+  var seedG = inputData[seedIdx + 1];
+  var seedB = inputData[seedIdx + 2];
+  var edge = [seed];
+  while (edge.length) {
+    var newedge = [];
+    for (var i = 0, ii = edge.length; i < ii; i++) {
+      // As noted in the Raster source constructor, this function is provided
+      // using the `lib` option. Other functions will NOT be visible unless
+      // provided using the `lib` option.
+      var next = nextEdges(edge[i]);
+      for (var j = 0, jj = next.length; j < jj; j++) {
+        var s = next[j][0], t = next[j][1];
+        if (s >= 0 && s < width && t >= 0 && t < height) {
+          var ci = (t * width + s) * 4;
+          var cr = inputData[ci];
+          var cg = inputData[ci + 1];
+          var cb = inputData[ci + 2];
+          var ca = inputData[ci + 3];
+          // if alpha is zero, carry on
+          if (ca === 0) {
+            continue;
+          }
+          if (Math.abs(seedR - cr) < delta && Math.abs(seedG - cg) < delta &&
+              Math.abs(seedB - cb) < delta) {
+            outputData[ci] = 255;
+            outputData[ci + 1] = 0;
+            outputData[ci + 2] = 0;
+            outputData[ci + 3] = 255;
+            newedge.push([s, t]);
+          }
+          // mark as visited
+          inputData[ci + 3] = 0;
+        }
+      }
+    }
+    edge = newedge;
+  }
+  return [new ImageData(outputData, width, height)];
+}
+
+function next4Edges(edge) {
+  var x = edge[0], y = edge[1];
+  return [
+    [x + 1, y],
+    [x - 1, y],
+    [x, y + 1],
+    [x, y - 1]
+  ];
+}
+
+var key = 'Ak-dzM4wZjSqTlzveKz5u0d4IQ4bRzVI309GxmkgSVr1ewS6iPSrOvOKhA-CJlm3';
+
+var imagery = new ol.layer.Tile({
+  source: new ol.source.BingMaps({key: key, imagerySet: 'Aerial'})
+});
+
+var raster = new ol.source.Raster({
+  sources: [imagery.getSource()],
+  operationType: 'image',
+  operations: [growRegion],
+  // the contents of `lib` option will be available to the operation(s) run in
+  // the web worker.
+  lib: {
+    nextEdges: next4Edges
+  }
+});
+
+var rasterImage = new ol.layer.Image({
+  opacity: 0.8,
+  source: raster
+});
+
+var map = new ol.Map({
+  layers: [imagery, rasterImage],
+  target: 'map',
+  view: new ol.View({
+    center: ol.proj.fromLonLat([-120, 50]),
+    zoom: 6
+  })
+});
+
+var pixel;
+
+map.getView().on('change', function() {
+  pixel = null;
+});
+
+map.on('click', function(ev) {
+  pixel = map.getPixelFromCoordinate(ev.coordinate);
+  raster.changed();
+});
+
+raster.on('beforeoperations', function(event) {
+  // the event.data object will be passed to operations
+  var data = event.data;
+  data.delta = thresholdControl.value;
+  data.pixel = pixel;
+});
+
+var thresholdControl = document.getElementById('threshold');
+
+function updateControlValue() {
+  document.getElementById('threshold-value').innerText = thresholdControl.value;
+}
+updateControlValue();
+
+thresholdControl.addEventListener('input', function() {
+  updateControlValue();
+  raster.changed();
+});