How to change Android Homescreen look?

Question

Each manufacturer makes a custom build of Android. Is this modification done in source or is it in app ?

If its in source : pointers to appropriate links would be useful.

Answer 1

It's called a launcher, which is a normal APK application. It's a normal Activity which reacts to a certain Intent.

You can create another one, and install it on your phone. When you press the home button it will ask which Launcher to use.

<activity
 android:label="@string/app_name"
 android:name=".ClassNameOfYourLauncher">
    <intent-filter >
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
    <intent-filter >
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.HOME" />
        <category android:name="android.intent.category.DEFAULT" />
    </intent-filter>
</activity>

Answer 2

I think you're talking about the Launcher. That's the first thing which comes to my mind. Its a System apk which will be there in app folder in system directory. If you need to modify that, you better create a new launcher of your own. Here is a link on how to go about doing that.