AndroidManifest.xml

<manifest
    xmlns:android="http://schemas.android.com/apk/res/android"
    package="sample.test"
    android:versionCode="1"
    android:versionName="1.0">

    <uses-sdk android:minSdkVersion="17" android:targetSdkVersion="17" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme"
        android:allowBackup="false">

        <service android:name="SampleDreamService">
            <intent-filter>
                <action android:name="android.service.dreams.DreamService" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>

            <meta-data android:name="android.service.dream" android:resource="@xml/dream" />
        </service>
    </application>
</manifest>

dream.xml

<dream xmlns:android="https://schemas.android.com/apk/res/android" />

SampleDreamService.java

package sample.test;

import android.service.dreams.DreamService;

public class SampleDreamService extends DreamService {
    @Override
    public void onAttachedToWindow() {
        super.onAttachedToWindow();

        setInteractive(false);
        setFullscreen(true);
        setContentView(new SampleView(this));
    }
}

SampleView.java

package sample.test;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class SampleView extends SurfaceView implements SurfaceHolder.Callback {

    private static final String TAG = "SampleView";

    private static final int[] colors = new int[]{
        Color.RED,
        Color.WHITE,
        Color.BLUE,
        Color.GREEN,
        Color.YELLOW
    };

    private int width;
    private int height;
    private SurfaceHolder holder;

    public SampleView(Context ctx) {
        super(ctx);

        holder = getHolder();
        holder.addCallback(this);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder2) {
        Log.v(TAG, "surfaceCreated");

        new Thread() {
            @Override
            public void run() {
                Paint paint = new Paint();
                paint.setAntiAlias(true);

                Canvas c = null;

                while (true) {
                    c = holder.lockCanvas();

                    if (c == null) {
                        break;
                    }

                    float x = (float)(Math.random() * width);
                    float y = (float)(Math.random() * height);

                    paint.setColor(getColor());

                    c.drawCircle(x, y, 5f, paint);

                    holder.unlockCanvasAndPost(c);

                }
            }
        }.start();
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        Log.v(TAG, "surfaceChanged");

        this.width = width;
        this.height = height;
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        Log.v(TAG, "surfaceDestroyed");
    }

    private int getColor() {
        int color = (int)(Math.random() * colors.length);

        return colors[color];
    }
}