add basic collision resolution

lib/systems/resolve-collisions.js

@@ -0,0 +1,61 @@
+"use strict";
+
+/**
+* System that looks for an entity with the {@link Components.collisons}, {@link Components.velocity}, {@link Components.lastPosition}, {@link Components.position}, and {@link Components.size} components.
+* Every frame the resolveCollisions system will check to see if any applicable entities are intersecting with an entity with the component {@link Components.body}, and if they are it will reset them to previous position either left, right, above, or below the other each other appropriately.
+* @memberof Systems
+* @alias resolveCollisions
+* @requires Systems.lastPosition
+* @see [addEach]{@link https://github.com/ericlathrop/entity-component-system#addeachsystem-search}
+* @see [registerSearch]{@link https://github.com/ericlathrop/entity-component-system#registersearchsearch-components}
+*/
+
+function wasLeft(entityLastPosition, entitySize, otherPosition) {
+	return entityLastPosition.x + entitySize.width <= otherPosition.x;
+}
+function wasRight(entityLastPosition, otherPosition, otherSize) {
+	return entityLastPosition.x >= otherPosition.x + otherSize.width;
+}
+function wasAbove(entityLastPosition, entitySize, otherPosition) {
+	return entityLastPosition.y + entitySize.height <= otherPosition.y;
+}
+function wasBelow(entityLastPosition, otherPosition, otherSize) {
+	return entityLastPosition.y >= otherPosition.y + otherSize.height;
+}
+
+module.exports = function(ecs, game) { // eslint-disable-line no-unused-vars
+	game.entities.registerSearch("resolveCollisionsSearch", ["collisions","velocity","lastPosition","position","size"]);
+	ecs.addEach(function resolveCollisions(entity, elapsed) { // eslint-disable-line no-unused-vars
+		var entityCollisions = game.entities.get(entity, "collisions");
+		var entityPosition = game.entities.get(entity, "position");
+		var entitySize = game.entities.get(entity, "size");
+		var entityVelocity = game.entities.get(entity, "velocity");
+		var entityLastPosition = game.entities.get(entity, "lastPosition");
+
+		for (var i = 0; i < entityCollisions.length; i++) {
+			var other = entityCollisions[i];
+			if (game.entities.get(other, "body")) {
+				var otherPosition = game.entities.get(other, "position");
+				var otherSize = game.entities.get(other, "size");
+
+				if (wasLeft(entityLastPosition, entitySize, otherPosition)) {
+					entityPosition.x = otherPosition.x - entitySize.width;
+					entityVelocity.x = 0;
+				}
+				if (wasRight(entityLastPosition, otherPosition, otherSize)) {
+					entityPosition.x = otherPosition.x + otherSize.width;
+					entityVelocity.x = 0;
+				}
+				if (wasAbove(entityLastPosition, entitySize, otherPosition)) {
+					entityPosition.y = otherPosition.y - entitySize.height;
+					entityVelocity.y = 0;
+				}
+				if (wasBelow(entityLastPosition, otherPosition, otherSize)) {
+					entityPosition.y = otherPosition.y + otherSize.height;
+					entityVelocity.y = 0;
+				}
+			}
+		}
+	}, "resolveCollisionsSearch");
+
+};

lib/systems/track-last-position.js

@@ -0,0 +1,18 @@
+"use strict";
+
+/**
+* System that looks for an entity with the {@link Components.collisions}, {@link Components.position}, and {@link Components.size} components.
+* Every frame the trasckLastPosition system will store the current position in a temporary component named "lastPosition". This is required for using the system resolveCollisions.
+* @memberof Systems
+* @alias trackLastPosition
+* @see [addEach]{@link https://github.com/ericlathrop/entity-component-system#addeachsystem-search}
+* @see [registerSearch]{@link https://github.com/ericlathrop/entity-component-system#registersearchsearch-components}
+*/
+
+module.exports = function(ecs, game) { // eslint-disable-line no-unused-vars
+	game.entities.registerSearch("trackLastPositionSearch",["collisions", "position", "size"]);
+	ecs.addEach(function trackLastPosition(entity, elapsed) { // eslint-disable-line no-unused-vars
+		var position = game.entities.get(entity, "position");
+		game.entities.set(entity, "lastPosition", { x: position.x, y: position.y });
+	}, "trackLastPositionSearch");
+};