A German XCode 3.2 Tutorial

XCode 3.2 Tutorial (German) for the absolute beginner (draft). 
 https://docs.google.com/open?id=0BwDaM24RKYS4Y0dsbXZFSW5SaFk


 

Clojure macro for LibGDX input polling

A very simple macro:

(defmacro when-pressed
  ([key form]
  `(when (.isKeyPressed Gdx/input (. com.badlogic.gdx.Input$Keys ~key))
     ~form))
  ([key form & rest]
     `(do
        (when-pressed ~key ~form)
        (when-pressed ~@rest))))

example usage:

 (when-pressed LEFT  (do-something)
               RIGHT (do-something-different)
               SPACE ( ... )
               ...)

expands to:

user=> (pprint (macroexpand-1 '(when-pressed LEFT (do-something))))
(clojure.core/when
 (.isKeyPressed Gdx/input (. com.badlogic.gdx.Input$Keys LEFT))
 (do-something))
nil

or

user=> (pprint (macroexpand-1 '(when-pressed LEFT (do-something)
                                             RIGHT (do-something-else))))
(do
 (when-pressed LEFT (do-something))
 (when-pressed RIGHT (do-something-else)))
nil

Android: A two column ListView with an ImageView

Struggling with ListViews and SimpleAdapters on Android, I came up with the following simple example of a ListView with two columns: an image and some text. In res/layout, create a xml list_item.xml for the listview items:

<?xml version="1.0" encoding="utf-8"?>
<!-- list_item.xml -->
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:paddingTop="4dip"
    android:paddingBottom="6dip"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:background="#ffffff"
    android:orientation="horizontal">
    <ImageView android:layout_width="100px"
       android:layout_height="50px"
       android:layout_gravity="left"
       android:id="@+id/LOGO_CELL"
       />
    <TextView android:id="@+id/TEXT_CELL"
       android:layout_height="wrap_content"
       android:layout_width="wrap_content"
       android:textColor="#000000"
       android:layout_gravity="center"
       android:layout_weight="1"/>

</LinearLayout>

Add a ListView to main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
  <TextView
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:text="Some Text"
      />
  <ListView  android:id="@+id/LISTVIEW"
      android:orientation="horizontal"
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"
   >
  </ListView>
</LinearLayout>

Finally, the code:

(ns com.example.android.ListExample 
  (:gen-class
   :extends android.app.Activity
   :exposes-methods {onCreate superOnCreate}
  (:import (android.app Activity)
           (android.os Bundle))))

(defn -onCreate  [this bundle]
    (.superOnCreate this bundle )
    (.setContentView this com.example.android.R$layout/main)
    (let [ids (int-array [com.example.android.R$id/LOGO_CELL
                          com.example.android.R$id/TEXT_CELL])
          names (into-array ["logo" "text"])
          thelist (java.util.ArrayList.
                   [{"logo" com.example.android.R$drawable/logo1 "text" "Text 1"}
                    {"logo" com.example.android.R$drawable/logo2 "text" "Text 2"}]
                   aa (android.widget.SimpleAdapter. this thelist
                                                     com.example.android.R$layout/list_item names ids)]
      (.setAdapter (.findViewById this com.example.android.R$id/LISTVIEW) aa)))
          

This will find the two pngs "logo1.png" and "logo2.png" in the res/drawable folders.

Box2D LibGDX Clojure Demo

LibGDX Triangle Example in Clojure

I started messing around with LibGDX with Clojure and came up with this translation of LibGDX's  example MyFirstTriangle.

There might be a bug in Clojure 1.3 with short arrays (?). While

float-array [0.5 0.5 0.5]

works,

short-array [0 1 2]

does not (exception).

(ns gdx1
  (:import (com.badlogic.gdx ApplicationListener Gdx)
           (com.badlogic.gdx.graphics GL10 Mesh VertexAttribute)
           (com.badlogic.gdx.backends.lwjgl LwjglApplication)))

(defn app-listener []
  (let [vertices (float-array [-0.5 -0.5 0 0.5 -0.5 0 0 0.5 0])
        triangles (into-array Short/TYPE [0 1 2])
        attrs (into-array VertexAttribute
         [(VertexAttribute.
           com.badlogic.gdx.graphics.VertexAttributes$Usage/Position
           3 "a_position")])
        mesh (ref nil)]
    (proxy [ApplicationListener] []
    (resize [w h] )
    (create []
      (let [m (doto (Mesh. true 3 3 attrs)
                (.setVertices vertices)
                (.setIndices triangles))]
      (dosync ( ref-set mesh m))))
    (render []
      (doto (Gdx/gl)
        (.glClear GL10/GL_COLOR_BUFFER_BIT))
     (doto @mesh
       (.render GL10/GL_TRIANGLES 0 3)))
    (pause [] )
    (resume [] )
    (dispose [] ))))

(defn App []
  (LwjglApplication. (app-listener) "My Game" 480 320 false))

This works fine in the repl. For Android, we would need to generate real classes, like so:

(ns net.thomas.android.MyFirstTriangle
  (:gen-class
   :extends com.badlogic.gdx.backends.android.AndroidApplication
   :exposes-methods {onCreate superOnCreate})
  (:import (android.os Bundle)
           (net.thomas.android Gdx1)
           (com.badlogic.gdx Gdx)
           (com.badlogic.gdx.backends.android AndroidApplication)))

(defn -onCreate [this bundle]
  (.superOnCreate this bundle)
  (.initialize this (Gdx1.) false))

and

(ns net.thomas.android.Gdx1
  (:gen-class
   :implements [com.badlogic.gdx.ApplicationListener]
  (:import (com.badlogic.gdx ApplicationListener Gdx)
           (com.badlogic.gdx.graphics GL10 Mesh VertexAttribute)))

(def vertices (float-array [-0.5 -0.5 0 0.5 -0.5 0 0 0.5 0]))
(def triangles (into-array Short/TYPE [0 1 2]))
(def mesh (ref nil))

(defn -resize [_ w h] )

(defn -create [_]
  (let [attrs (into-array VertexAttribute
                          [(VertexAttribute.
                            com.badlogic.gdx.graphics.VertexAttributes$Usage/Position
                            3 "a_position")])
        m (doto (Mesh. true 3 3 attrs)
            (.setVertices vertices)
            (.setIndices triangles))]
    (dosync (ref-set mesh m))))

(defn -render [_]
  (doto (Gdx/gl)
    (.glClear GL10/GL_COLOR_BUFFER_BIT))
  (doto @mesh
    (.render GL10/GL_TRIANGLES 0 3)))

(defn -pause [_] )
(defn -resume [_] )
(defn -dispose [_] )

How to use Apache Httpget in Clojure

Clojure's slurp function is great for quick retrieval of websites, but sometimes it's not enough and you'll get an 403 error.

As a quick fix I suggest using the Apache httpclient library. You will need httpclient-4.x.x.jar, httpcore-4.x.x.jar and commons-logging-1.x.x.jar in your classpath, which you can find here:

• http://hc.apache.org/httpcomponents-client-ga/httpclient/index.html
• http://commons.apache.org/logging/ 
• http://hc.apache.org/ 

 The function http-get is a simple replacement for slurp. You can easily extend, e.g. adding timeouts, etc.

(ns apache-http
  (:import
   (org.apache.http.client ResponseHandler HttpClient methods.HttpGet)
   (org.apache.http.impl.client BasicResponseHandler DefaultHttpClient)))

(defn http-get [ url ]
  (let [client (DefaultHttpClient.)
        httpget (HttpGet. url)
        handler (BasicResponseHandler.)]
    (try 
      (let [body (.execute client httpget handler)]
        body)
      (catch Exception e (println e))
      (finally
        (println "shutdown connection")
        (.shutdown (.getConnectionManager client))
        )) ))

usage is simple:

(http-get "http://www.google.com")

A template for binomial coefficients in C++

Here's how you could implement a compile time calculation of
binomial numbers "n over k" in C++ with a template.

#ifndef BINOMIAL_HPP_INCLUDED

#define BINOMIAL_HPP_INCLUDED


template<int n, int k>
struct Binomial
{
  const static int value =  (Binomial<n-1,k-1>::value + Binomial<n-1,k>::value);
};

template<>
struct Binomial<0,0>
{
  const static int value = 1;
};

template<int n>
struct Binomial<n,0>
{
  const static int value = 1;
};

template<int n>
struct Binomial<n,n>
{
  const static int value = 1;
};

template<int n, int k>
inline int binomial()
{
  return Binomial<n,k>::value;
}

#endif

Now let's try it with a short main:

#include "Binomial.hpp"
#include <iostream>

int main()
{
  std::cout << "30 over 15: " << binomial<30,15>() << std::endl;
  return 0;
}
  

30 over 15: 155117520

It works! When it will break depends on your compiler. I used g++ 4.6.2