From 3393a4479ec9d7ddaa3ceb39b20bf0af353cf010 Mon Sep 17 00:00:00 2001
From: BlackMATov <blackmatov@gmail.com>
Date: Fri, 28 Dec 2018 09:42:34 +0700
Subject: [PATCH] basic usage example

---
 README.md     | 61 +++++++++++++++++++++++++++++++++++++++++++++++++--
 ecs_tests.cpp | 59 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 118 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 9adeaf2..5ac6014 100644
--- a/README.md
+++ b/README.md
@@ -31,9 +31,66 @@
 #include "ecs.hpp"
 ```
 
-## Examples
+## Basic usage
 
-> coming soon!
+```cpp
+struct position_component {
+    float x{0};
+    float y{0};
+    position_component(float nx, float ny)
+    : x(nx), y(ny) {}
+};
+
+struct velocity_component {
+    float dx{0};
+    float dy{0};
+    velocity_component(float ndx, float ndy)
+    : dx(ndx), dy(ndy) {}
+};
+
+class movement_system : public ecs_hpp::system {
+public:
+    void process(ecs_hpp::registry& owner) override {
+        owner.for_joined_components<
+            position_component,
+            velocity_component
+        >([](const ecs_hpp::entity& e, position_component& p, const velocity_component& v) {
+            p.x += v.dx;
+            p.y += v.dy;
+        });
+    }
+};
+
+class gravity_system : public ecs_hpp::system {
+public:
+    gravity_system(float gravity)
+    : gravity_(gravity) {}
+
+    void process(ecs_hpp::registry& owner) override {
+        owner.for_each_component<
+            velocity_component
+        >([this](const ecs_hpp::entity& e, velocity_component& v) {
+            v.dx += gravity_;
+            v.dy += gravity_;
+        });
+    }
+private:
+    float gravity_;
+};
+
+ecs_hpp::registry world;
+world.add_system<movement_system>();
+
+auto entity_one = world.create_entity();
+world.assign_component<position_component>(entity_one, 4.f, 2.f);
+world.assign_component<velocity_component>(entity_one, 10.f, 20.f);
+
+auto entity_two = world.create_entity();
+entity_two.assign_component<position_component>(4.f, 2.f);
+entity_two.assign_component<velocity_component>(10.f, 20.f);
+
+world.process_systems();
+```
 
 ## API
 
diff --git a/ecs_tests.cpp b/ecs_tests.cpp
index e36c0cc..21fe6e2 100644
--- a/ecs_tests.cpp
+++ b/ecs_tests.cpp
@@ -699,3 +699,62 @@ TEST_CASE("registry") {
         }
     }
 }
+
+TEST_CASE("example") {
+    struct position_component {
+        float x{0};
+        float y{0};
+        position_component(float nx, float ny)
+        : x(nx), y(ny) {}
+    };
+
+    struct velocity_component {
+        float dx{0};
+        float dy{0};
+        velocity_component(float ndx, float ndy)
+        : dx(ndx), dy(ndy) {}
+    };
+
+    class movement_system : public ecs_hpp::system {
+    public:
+        void process(ecs_hpp::registry& owner) override {
+            owner.for_joined_components<
+                position_component,
+                velocity_component
+            >([](const ecs_hpp::entity& e, position_component& p, const velocity_component& v) {
+                p.x += v.dx;
+                p.y += v.dy;
+            });
+        }
+    };
+
+    class gravity_system : public ecs_hpp::system {
+    public:
+        gravity_system(float gravity)
+        : gravity_(gravity) {}
+
+        void process(ecs_hpp::registry& owner) override {
+            owner.for_each_component<
+                velocity_component
+            >([this](const ecs_hpp::entity& e, velocity_component& v) {
+                v.dx += gravity_;
+                v.dy += gravity_;
+            });
+        }
+    private:
+        float gravity_;
+    };
+
+    ecs_hpp::registry world;
+    world.add_system<movement_system>();
+
+    auto entity_one = world.create_entity();
+    world.assign_component<position_component>(entity_one, 4.f, 2.f);
+    world.assign_component<velocity_component>(entity_one, 10.f, 20.f);
+
+    auto entity_two = world.create_entity();
+    entity_two.assign_component<position_component>(4.f, 2.f);
+    entity_two.assign_component<velocity_component>(10.f, 20.f);
+
+    world.process_systems();
+}