add applyScale system

lib/systems/apply-scale.js

@@ -0,0 +1,36 @@
+"use strict";
+
+module.exports = function(ecs, game) { // eslint-disable-line no-unused-vars
+  game.entities.registerSearch("applyScale", ["scale", "size"]);
+  ecs.addEach(function applyScale(entity, elapsed) { // eslint-disable-line no-unused-vars
+    var scale = game.entities.get(entity, "scale");
+    if (scale.last) {
+      if (scale.last !== scale.current) {
+        scaleWithMax(game, entity, scale);
+      }
+    } else {
+      var size = game.entities.get(entity, "size");
+      game.entities.set(entity, "originalSize", size);
+      scaleWithMax(game, entity, scale);
+    }
+  }, "applyScale");
+};
+
+function scaleWithMax(game, entity, scale) {
+  if (scale.max) {
+    if (scale.current < scale.max) {
+      scaleEntity(game, entity, scale);
+    }
+  } else {
+    scaleEntity(game, entity, scale);
+  }
+}
+
+function scaleEntity(game, entity, scale) {
+  var originalSize = game.entities.get(entity, "originalSize");
+  game.entities.set(entity, "size", {
+    "width": originalSize.width * scale.current,
+    "height": originalSize.height * scale.current
+  });
+  scale.last = scale.current;
+}