feat(auto-place): add feature

Related to bpmn-io/dmn-js#470

lib/features/auto-place/AutoPlace.js

@@ -0,0 +1,93 @@
+import {
+  asTRBL,
+  getMid
+} from '../../layout/LayoutUtil';
+
+import { DEFAULT_DISTANCE } from './AutoPlaceUtil';
+
+var LOW_PRIORITY = 100;
+
+
+/**
+ * A service that places elements connected to existing ones
+ * to an appropriate position in an _automated_ fashion.
+ *
+ * @param {EventBus} eventBus
+ * @param {Modeling} modeling
+ */
+export default function AutoPlace(eventBus, modeling) {
+
+  eventBus.on('autoPlace', LOW_PRIORITY, function(context) {
+    var shape = context.shape,
+        source = context.source;
+
+    return getNewShapePosition(source, shape);
+  });
+
+  /**
+   * Append shape to source at appropriate position.
+   *
+   * @param {djs.model.Shape} source
+   * @param {djs.model.Shape} shape
+   *
+   * @return {djs.model.Shape} appended shape
+   */
+  this.append = function(source, shape, hints) {
+
+    eventBus.fire('autoPlace.start', {
+      source: source,
+      shape: shape
+    });
+
+    // allow others to provide the position
+    var position = eventBus.fire('autoPlace', {
+      source: source,
+      shape: shape
+    });
+
+    var newShape = modeling.appendShape(source, shape, position, source.parent, hints);
+
+    eventBus.fire('autoPlace.end', {
+      source: source,
+      shape: newShape
+    });
+
+    return newShape;
+  };
+
+}
+
+AutoPlace.$inject = [
+  'eventBus',
+  'modeling'
+];
+
+// helpers //////////
+
+/**
+ * Find the new position for the target element to
+ * connect to source.
+ *
+ * @param  {djs.model.Shape} source
+ * @param  {djs.model.Shape} element
+ * @param  {Object} [hints]
+ * @param  {Object} [hints.defaultDistance]
+ *
+ * @returns {Point}
+ */
+export function getNewShapePosition(source, element, hints) {
+  if (!hints) {
+    hints = {};
+  }
+
+  var distance = hints.defaultDistance || DEFAULT_DISTANCE;
+
+  var sourceMid = getMid(source),
+      sourceTrbl = asTRBL(source);
+
+  // simply put element right next to source
+  return {
+    x: sourceTrbl.right + distance + element.width / 2,
+    y: sourceMid.y
+  };
+}

lib/features/auto-place/AutoPlaceSelectionBehavior.js

@@ -0,0 +1,18 @@
+/**
+ * Select element after auto placement.
+ *
+ * @param {EventBus} eventBus
+ * @param {Selection} selection
+ */
+export default function AutoPlaceSelectionBehavior(eventBus, selection) {
+
+  eventBus.on('autoPlace.end', 500, function(e) {
+    selection.select(e.shape);
+  });
+
+}
+
+AutoPlaceSelectionBehavior.$inject = [
+  'eventBus',
+  'selection'
+];