Preview polygons in the map before generating them.

farm_area_generate/farm_area_generate.module

@@ -44,6 +44,13 @@ function farm_area_generate_menu() {
     'type' => MENU_LOCAL_TASK,
   );
 
+  // Area generator callback.
+  $items['farm/areas/generate/callback'] = array(
+    'page callback' => 'farm_area_generate_callback',
+    'access arguments' => array('use farm area generator'),
+    'type' => MENU_CALLBACK,
+  );
+
   return $items;
 }
 
@@ -66,6 +73,15 @@ function farm_area_generate_form($form, &$form_state) {
   // Add javascript.
   drupal_add_js(drupal_get_path('module', 'farm_area_generate') . '/js/farm_area_generate.js');
 
+  // Hidden field for generated area WKT. If the areas were generated via the
+  // "Preview" button, WKT will be stored in $form_state['storage']['wkt'].
+  $form['wkt'] = array(
+    '#type' => 'hidden',
+    '#value' => !empty($form_state['storage']['wkt']) ? $form_state['storage']['wkt'] : '',
+    '#prefix' => '<div id="generated-wkt">',
+    '#suffix' => '</div>',
+  );
+
   // Area select.
   $form['area'] = array(
     '#type' => 'textfield',
@@ -108,6 +124,14 @@ function farm_area_generate_form($form, &$form_state) {
     drupal_set_message('This area generator tool requires the GEOS libary: ' . l('http://trac.osgeo.org/geos', 'http://trac.osgeo.org/geos'), 'warning');
   }
   else {
+    $form['actions']['preview'] = array(
+      '#type' => 'submit',
+      '#value' => t('Preview'),
+      '#submit' => array('farm_area_generate_form_preview'),
+      '#ajax' => array(
+        'callback' => 'farm_area_generate_form_ajax',
+      ),
+    );
     $form['actions']['submit'] = array(
       '#type' => 'submit',
       '#value' => t('Generate'),
@@ -124,6 +148,31 @@ function farm_area_generate_form($form, &$form_state) {
   return $form;
 }
 
+/**
+ * Ajax callback for farm_area_generate_form().
+ */
+function farm_area_generate_form_ajax($form, $form_state) {
+
+  // Get the "wkt" form element and CSS selector.
+  $element = $form['wkt'];
+  $selector = '#generated-wkt';
+
+  // Assemble commands...
+  $commands = array();
+
+  // Replace the hidden field.
+  $commands[] = ajax_command_replace($selector, render($element));
+
+  // Execute Javascript to add WKT to the map.
+  $commands[] = array('command' => 'farmAreaGeneratePreview');
+
+  // Display status messages.
+  $commands[] = ajax_command_prepend($selector, theme('status_messages'));
+
+  // Return ajax commands.
+  return array('#type' => 'ajax', '#commands' => $commands);
+}
+
 /**
  * Area generator form validate.
  */
@@ -187,6 +236,34 @@ function farm_area_generate_form_validate(&$form, &$form_state) {
   }
 }
 
+/**
+ * Farm area generator form preview.
+ */
+function farm_area_generate_form_preview(&$form, &$form_state) {
+
+  // If the area and polygon was not stored in validation, bail.
+  if (empty($form_state['storage']['area']) || empty($form_state['storage']['polygon'])) {
+    return;
+  }
+
+  // Get all the necessary variables from the form state.
+  $polygon = $form_state['storage']['polygon'];
+  $count = $form_state['values']['count'];
+  $orientation = $form_state['values']['orientation'];
+
+  // Generate child area geometries.
+  $geometries = farm_area_generate_geometries($polygon, $count, $orientation);
+  if (!empty($geometries)) {
+    $collection = new GeometryCollection($geometries);
+    $form_state['storage']['wkt'] = $collection->asText();
+  }
+
+  // Rebuild the form if WKT was generated.
+  if (!empty($form_state['storage']['wkt'])) {
+    $form_state['rebuild'] = TRUE;
+  }
+}
+
 /**
  * Farm area generate form submit.
  */

farm_area_generate/js/farm_area_generate.js

@@ -2,6 +2,9 @@
   Drupal.behaviors.farm_area_generate = {
     attach: function (context, settings) {
 
+      // Initialize a setting for storing the temporary preview layer.
+      Drupal.settings.farm_area_generate_preview_layer = Drupal.settings.farm_area_generate_preview_layer || {};
+
       // When an Openlayers popup is displayed, copy the area to the area
       // generator form field.
       $(document).on('openlayers.Component:Popup', function (event, options) {
@@ -12,4 +15,44 @@
       });
     }
   };
+
+  Drupal.farm_area_generate = {
+
+    // Function for adding WKT as a layer to the map.
+    preview: function (wkt) {
+
+      // Load the Openlayers map.
+      var map_id = $('.openlayers-map').attr('id');
+      var map = Drupal.openlayers.getMapById(map_id);
+
+      // If a bed layer was already added, remove it.
+      if (Drupal.settings.farm_area_generate_preview_layer) {
+        map.map.removeLayer(Drupal.settings.farm_area_generate_preview_layer);
+      }
+
+      // Generate a new layer from WKT.
+      var format = new ol.format.WKT();
+      var feature = format.readFeature(wkt, {
+        dataProjection: 'EPSG:4326',
+        featureProjection: 'EPSG:3857'
+      });
+      Drupal.settings.farm_area_generate_preview_layer = new ol.layer.Vector({
+        source: new ol.source.Vector({
+          features: [feature]
+        })
+      });
+
+      // Add layer to the map.
+      map.map.addLayer(Drupal.settings.farm_area_generate_preview_layer);
+    }
+  };
+
+  // Define a Drupal ajax command for loading the wkt from the hidden input
+  // field and previewing it on the map.
+  Drupal.ajax.prototype.commands.farmAreaGeneratePreview = function() {
+    var wkt = $('#generated-wkt input[name="wkt"]').val();
+    if (wkt) {
+      Drupal.farm_area_generate.preview(wkt);
+    }
+  }
 }(jQuery));