1 files changed, 97 insertions, 0 deletions
diff --git a/lib/systems/apply_force.js b/lib/systems/apply_force.js
new file mode 100644
index 0000000..4adc55d
--- /dev/null
+++ b/lib/systems/apply_force.js
@@ -0,0 +1,97 @@
+import { System } from '@serpentity/serpentity';
+import { Body, Vector } from 'matter-js';
+
+const internals = {
+  kForce: 0.0001
+};
+
+import PhysicalWithExternalForceNode from '../nodes/physical_with_external_force';
+
+/**
+ * Applies physica from external forces (eg. controls) to the physics body
+ *
+ * @extends {external:Serpentity.System}
+ * @class ApplyForceSystem
+ * @param {object} config a configuration object to extend.
+ */
+export default class ApplyForceSystem extends System {
+
+  constructor(config = {}) {
+
+    super();
+
+    /**
+     * The node collection of entities that have external force
+     *
+     * @property {external:Serpentity.NodeCollection} physicalEntities
+     * @instance
+     * @memberof ApplyForceSystem
+     */
+    this.physicalEntities = null;
+  }
+
+  /**
+   * Initializes system when added. Requests physics nodes
+   *
+   * @function added
+   * @memberof ApplyForceSystem
+   * @instance
+   * @param {external:Serpentity.Engine} engine the serpentity engine to
+   * which we are getting added
+   */
+  added(engine) {
+
+    this.physicalEntities = engine.getNodes(PhysicalWithExternalForceNode);
+  }
+
+  /**
+   * Clears system resources when removed.
+   *
+   * @function removed
+   * @instance
+   * @memberof ApplyForceSystem
+   */
+  removed() {
+
+    this.physicalEntities = null;
+  }
+
+  /**
+   * Runs on every update of the loop. Updates the body based on the force
+   * component
+   *
+   * @function update
+   * @instance
+   * @param {Number} currentFrameDuration the duration of the current
+   * frame
+   * @memberof ApplyForceSystem
+   */
+  update(currentFrameDuration) {
+
+    for (const physicalEntity of this.physicalEntities) {
+      const body = physicalEntity.body.body;
+      const force = physicalEntity.force;
+      const forceVector = Vector.create(force.x * internals.kForce, force.y * internals.kForce);
+
+
+      // Store the last angle and apply force on non-zero forces
+
+      if (force.x || force.y) {
+        force.lastAngle = Math.atan2(force.y, force.x);
+        Body.applyForce(body,
+          {
+            x: body.position.x,
+            y: body.position.y
+          },
+          forceVector
+        );
+      }
+
+      // Reset the force
+
+      force.x = 0;
+      force.y = 0;
+    }
+  }
+};
+