From d78b02ff88b3669362648f0ad8c131188e770430 Mon Sep 17 00:00:00 2001
From: Stuart Campbell <stuart@harto.org>
Date: Mon, 1 Apr 2013 13:41:34 +1100
Subject: [PATCH] Initial thoughts on component-entity system

---
 common/src/clj/enoki/component_macros.clj   | 15 ++++++++
 common/src/cljx/enoki/entity.cljx           | 25 +++++++++++++
 example/common/src/cljx/game/component.cljx | 14 +++++++
 example/common/src/cljx/game/main.cljx      | 41 ++++++++++++++-------
 4 files changed, 82 insertions(+), 13 deletions(-)
 create mode 100644 common/src/clj/enoki/component_macros.clj
 create mode 100644 common/src/cljx/enoki/entity.cljx
 create mode 100644 example/common/src/cljx/game/component.cljx

diff --git a/common/src/clj/enoki/component_macros.clj b/common/src/clj/enoki/component_macros.clj
new file mode 100644
index 0000000..f359147
--- /dev/null
+++ b/common/src/clj/enoki/component_macros.clj
@@ -0,0 +1,15 @@
+(ns enoki.component-macros)
+
+(defmacro defcomponent
+  "Define a component-creation function, named by `type`, that accepts `params`
+   and returns a map consisting of the remaining key-value pairs. E.g.
+
+       (defcomponent foo [bar baz]
+         :bar bar
+         :baz (inc baz))
+
+       (foo :quux 2) ; => {:enoki.component/type :foo, :bar :quux, :baz 3}"
+  [type params & kvs]
+  `(defn ~type ~(vec params)
+     (into {:enoki.component/type ~(keyword type)}
+           (hash-map ~@kvs))))
diff --git a/common/src/cljx/enoki/entity.cljx b/common/src/cljx/enoki/entity.cljx
new file mode 100644
index 0000000..c864753
--- /dev/null
+++ b/common/src/cljx/enoki/entity.cljx
@@ -0,0 +1,25 @@
+;; Functions for initialising and managing entities.
+;; Entities are plain mappings of component types (keywords) to components (which
+;; are also maps).
+
+(ns enoki.entity)
+
+(let [next-id (atom 0)]
+  (defn uid
+    "Reserve and return a unique numeric ID."
+    []
+    (swap! next-id inc)))
+
+(defn new
+  "Initialise an entity with some collection of components. A unique ID is
+   assigned and accessible via `:id`. Components are accessible by their
+   name as a keyword; i.e. use `:foo` to fetch components defined using
+   `(defcomponent foo ...)`."
+  [& components]
+  (into {:id (uid)}
+        (map (fn [comp] [(:enoki.component/type comp) comp]) components)))
+
+(defn with-component
+  "Find all entities that include a component of a given type."
+  [entities component-type]
+  (filter #(contains? % component-type) entities))
diff --git a/example/common/src/cljx/game/component.cljx b/example/common/src/cljx/game/component.cljx
new file mode 100644
index 0000000..17d1f65
--- /dev/null
+++ b/example/common/src/cljx/game/component.cljx
@@ -0,0 +1,14 @@
+;; Game-specific components
+
+^:clj (ns game.component
+         (:use [enoki.component-macros :only [defcomponent]]))
+
+^:cljs (ns game.component
+         (:use-macros [enoki.component-macros :only [defcomponent]]))
+
+(defcomponent position [x y]
+  :x x
+  :y y)
+
+(defcomponent sprite [image-id]
+  :image-id image-id)
diff --git a/example/common/src/cljx/game/main.cljx b/example/common/src/cljx/game/main.cljx
index 7b7f458..36fb002 100644
--- a/example/common/src/cljx/game/main.cljx
+++ b/example/common/src/cljx/game/main.cljx
@@ -2,27 +2,32 @@
         (:require [clojure.string :as str]
                   [enoki.asset :as asset]
                   [enoki.engine :as enoki]
+                  [enoki.entity :as entity]
                   [enoki.event :as event]
                   [enoki.graphics :as gfx]
                   [enoki.logging]
-                  [enoki.logging-macros :as log])
+                  [enoki.logging-macros :as log]
+                  [game.component :as comp])
         (:use [enoki.core :only [now]]))
 
 ^:cljs (ns game.main
          (:require [clojure.string :as str]
                    [enoki.asset :as asset]
                    [enoki.engine :as enoki]
+                   [enoki.entity :as entity]
                    [enoki.event :as event]
                    [enoki.graphics :as gfx]
-                   [enoki.logging :as _])
+                   [enoki.logging :as _]
+                   [game.component :as comp])
          (:require-macros [enoki.logging-macros :as log])
          (:use [enoki.core :only [now]])
          (:use-macros [enoki.cljs-macros :only [double]]))
 
-;; ## Update
-
 (defn initial-state []
-  {:alien {:position {:x 10 :y 60}}})
+  {:entities [(entity/new (comp/sprite "images/alien.png")
+                          (comp/position 10 60))]})
+
+;; ## Update
 
 (defn movement [pressed-keys]
   (let [x-offsets {:left -1 :right 1}
@@ -39,25 +44,35 @@
 
 ;; ## Draw
 
-(defn print-fps [ctx fps]
+(defn image [state id]
+  (get-in state [:assets id]))
+
+(defn print-fps! [ctx fps]
   (gfx/draw-text! ctx (format "%03.1ffps" (double fps)) 10 20))
 
-(defn print-pressed-keys [ctx keys]
+(defn print-pressed-keys! [ctx keys]
   (gfx/draw-text! ctx (format "keys: %s" (str/join ", " keys)) 10 40))
 
+(defn draw-sprite! [ctx state entity]
+  (let [image-id (get-in entity [:sprite :image-id])
+        {:keys [x y]} (get entity :position)]
+    (gfx/draw-image! ctx (image state image-id) x y)))
+
+(defn draw-sprites! [ctx state]
+  (doseq [e (entity/with-component (:entities state) :sprite)]
+    (draw-sprite! ctx state e)))
+
 (defn render [state ctx]
   (-> ctx
       (gfx/clear!)
-      (print-fps (enoki/fps state))
-      (print-pressed-keys (:pressed-keys state))
-      (gfx/draw-image! (get-in state [:assets "images/alien.png"])
-                       (get-in state [:alien :x])
-                       (get-in state [:alien :y]))))
+      (print-fps! (enoki/fps state))
+      (print-pressed-keys! (:pressed-keys state))
+      (draw-sprites! state)))
 
 ;; ## Loop
 
 (defn enter-loop [env]
-  (event/subscribe! :update (fn [state _] (update state)))
+  ;(event/subscribe! :update (fn [state _] (update state)))
   (event/subscribe! :render (fn [state _ ctx] (render state ctx)))
   (enoki/start (assoc env :state
                       ;; FIXME: stupid hack to get assets into :state