1 files changed, 93 insertions, 0 deletions
diff --git a/lib/systems/elastic.js b/lib/systems/elastic.js
new file mode 100644
index 0000000..b94d371
--- /dev/null
+++ b/lib/systems/elastic.js
@@ -0,0 +1,93 @@
+import { System } from '@serpentity/serpentity';
+
+const internals = {
+  kTightStiffness: 0.001,
+  kBaseStiffness: 0.0008,
+  kLooseStiffness: 0.0000001
+};
+
+import ElasticNode from '../nodes/elastic';
+
+/**
+ Changes the stiffness on the node when it's less extended
+ *
+ * @extends {external:Serpentity.System}
+ * @class ElasticSystem
+ * @param {object} config a configuration object to extend.
+ */
+export default class ElasticSystem extends System {
+
+  constructor(config = {}) {
+
+    super();
+
+    /**
+     * The node collection of entities that have external force
+     *
+     * @property {external:Serpentity.NodeCollection} elastics
+     * @instance
+     * @memberof ElasticSystem
+     */
+    this.elastics = null;
+  }
+
+  /**
+   * Initializes system when added. Requests elastic nodes
+   *
+   * @function added
+   * @memberof ElasticSystem
+   * @instance
+   * @param {external:Serpentity.Engine} engine the serpentity engine to
+   * which we are getting added
+   */
+  added(engine) {
+
+    this.elastics = engine.getNodes(ElasticNode);
+  }
+
+  /**
+   * Clears system resources when removed.
+   *
+   * @function removed
+   * @instance
+   * @memberof ElasticSystem
+   */
+  removed() {
+
+    this.elastics = null;
+  }
+
+  /**
+   * Runs on every update of the loop. Checks length of elastic and adjusts
+   * stiffness
+   *
+   * @function update
+   * @instance
+   * @param {Number} currentFrameDuration the duration of the current
+   * frame
+   * @memberof ElasticSystem
+   */
+  update(currentFrameDuration) {
+
+    for (const elastic of this.elastics) {
+      const constraint = elastic.body.body;
+
+      const currentDistance = Math.abs(
+        Math.sqrt(
+          Math.pow(constraint.bodyA.position.x - constraint.bodyB.position.x, 2) +
+          Math.pow(constraint.bodyA.position.y - constraint.bodyB.position.y, 2)));
+
+      if (currentDistance <= constraint.length) {
+        constraint.stiffness = internals.kLooseStiffness;
+        continue;
+      }
+
+      if (currentDistance >= 2.6 * constraint.length) {
+        constraint.stiffness = internals.kTightStiffness;
+        continue;
+      }
+
+      constraint.stiffness = internals.kBaseStiffness;
+    }
+  }
+};