feat: add distribution buttons to multi-element context pad

Closes #1680

lib/features/distribute-elements/DistributeElementsContextPadProvider.js

@@ -0,0 +1,68 @@
+import ICONS from './DistributeElementsIcons';
+
+import { assign } from 'min-dash';
+
+var LOW_PRIORITY = 900;
+
+/**
+ * A provider for distribute elements context pad
+ */
+export default function DistributeElementsContextPadProvider(contextPad, distributeElements, translate) {
+
+  contextPad.registerProvider(LOW_PRIORITY, this);
+
+  this._contextPad = contextPad;
+
+  this._distributeElements = distributeElements;
+  this._translate = translate;
+}
+
+DistributeElementsContextPadProvider.$inject = [
+  'contextPad',
+  'distributeElements',
+  'translate'
+];
+
+DistributeElementsContextPadProvider.prototype.getMultiElementContextPadEntries = function(elements) {
+  var actions = {};
+
+  if (this._isAllowed(elements)) {
+    assign(actions, this._getEntries(elements));
+  }
+
+  return actions;
+};
+
+DistributeElementsContextPadProvider.prototype._isAllowed = function(elements) {
+  return true;
+};
+
+DistributeElementsContextPadProvider.prototype._getEntries = function(elements) {
+  var distributeElements = this._distributeElements,
+      translate = this._translate;
+
+  var entries = {
+    'distribute-elements-horizontally': {
+      group: 'distribute',
+      title: translate('Distribute elements horizontally'),
+      imageUrl: ICONS['horizontal'],
+      action: {
+        click: function(event, elements) {
+          distributeElements.trigger(elements, 'horizontal');
+        }
+      }
+    },
+    'distribute-elements-vertically': {
+      group: 'distribute',
+      title: translate('Distribute elements vertically'),
+      imageUrl: ICONS['vertical'],
+      action: {
+        click: function(event, elements) {
+          distributeElements.trigger(elements, 'vertical');
+        }
+      }
+    },
+  };
+
+  return entries;
+};

lib/features/distribute-elements/index.js

@@ -1,12 +1,19 @@
 import DistributeElementsModule from 'diagram-js/lib/features/distribute-elements';
+import ContextPadModule from 'diagram-js/lib/features/context-pad';
 
 import BpmnDistributeElements from './BpmnDistributeElements';
+import DistributeElementsContextPadProvider from './DistributeElementsContextPadProvider';
 
 
 export default {
   __depends__: [
+    ContextPadModule,
     DistributeElementsModule
   ],
-  __init__: [ 'bpmnDistributeElements' ],
-  bpmnDistributeElements: [ 'type', BpmnDistributeElements ]
+  __init__: [
+    'bpmnDistributeElements',
+    'distributeElementsContextPadProvider'
+  ],
+  bpmnDistributeElements: [ 'type', BpmnDistributeElements ],
+  distributeElementsContextPadProvider: [ 'type', DistributeElementsContextPadProvider ]
 };