docs/html/training/graphics/opengl/environment.jd

page.title=Building an OpenGL ES Environment
parent.title=Displaying Graphics with OpenGL ES
parent.link=index.html

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previous.title=Displaying Graphics with OpenGL ES
previous.link=index.html
next.title=Defining Shapes
next.link=shapes.html

@jd:body

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<h2>This lesson teaches you to</h2>
<ol>
  <li><a href="#manifest">Declare OpenGL ES Use in the Manifest</a></li>
  <li><a href="#activity">Create an Activity for OpenGL ES Graphics</a></li>
  <li><a href="#glsurfaceview">Build a GLSurfaceView Object</a></li>
  <li><a href="#renderer">Build a Renderer Class</a></li>
</ol>

<h2>You should also read</h2>
<ul>
  <li><a href="{@docRoot}guide/topics/graphics/opengl.html">OpenGL</a></li>
</ul>

<h2>Try it out</h2>

<div class="download-box">
 <a href="{@docRoot}shareables/training/OpenGLES.zip"
class="button">Download the sample</a>
 <p class="filename">OpenGLES.zip</p>
</div>

</div>
</div>


<p>In order to draw graphics with OpenGL ES in your Android application, you must create a
view container for them. One of the more straight-forward ways to do this is to implement both a
{@link android.opengl.GLSurfaceView} and a {@link android.opengl.GLSurfaceView.Renderer}. A {@link
android.opengl.GLSurfaceView} is a view container for graphics drawn with OpenGL and {@link
android.opengl.GLSurfaceView.Renderer} controls what is drawn within that view. For more information
about these classes, see the <a href="{@docRoot}guide/topics/graphics/opengl.html">OpenGL ES</a>
developer guide.</p>

<p>{@link android.opengl.GLSurfaceView} is just one way to incorporate OpenGL ES graphics into your
application. For a full-screen or near-full screen graphics view, it is a reasonable choice.
Developers who want to incorporate OpenGL ES graphics in a small portion of their layouts should
take a look at {@link android.view.TextureView}. For real, do-it-yourself developers, it is also
possible to build up an OpenGL ES view using {@link android.view.SurfaceView}, but this requires
writing quite a bit of additional code.</p>

<p>This lesson explains how to complete a minimal implementation of {@link
android.opengl.GLSurfaceView} and {@link android.opengl.GLSurfaceView.Renderer} in a simple
application activity.</p>


<h2 id="manifest">Declare OpenGL ES Use in the Manifest</h2>

<p>In order for your application to use the OpenGL ES 2.0 API, you must add the following
declaration to your manifest:</p>

<pre>
&lt;uses-feature android:glEsVersion="0x00020000" android:required="true" /&gt;
</pre>

<p>If your application uses texture compression, you must also declare which compression formats
your app supports, so that it is only installed on compatible devices.</p>

<pre>
&lt;supports-gl-texture android:name="GL_OES_compressed_ETC1_RGB8_texture" /&gt;
&lt;supports-gl-texture android:name="GL_OES_compressed_paletted_texture" /&gt;
</pre>

<p>For more information about texture compression formats, see the
<a href="{@docRoot}guide/topics/graphics/opengl.html#textures">OpenGL</a> developer guide.</p>


<h2 id="activity">Create an Activity for OpenGL ES Graphics</h2>

<p>Android applications that use OpenGL ES have activities just like any other application that has
a user interface. The main difference from other applications is what you put in the layout for your
activity. While in many applications you might use {@link android.widget.TextView}, {@link
android.widget.Button} and {@link android.widget.ListView}, in an app that uses OpenGL ES, you can
also add a {@link android.opengl.GLSurfaceView}.</p>

<p>The following code example shows a minimal implementation of an activity that uses a
{@link android.opengl.GLSurfaceView} as its primary view:</p>

<pre>
public class OpenGLES20Activity extends Activity {

    private GLSurfaceView mGLView;

    &#64;Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Create a GLSurfaceView instance and set it
        // as the ContentView for this Activity.
        mGLView = new MyGLSurfaceView(this);
        setContentView(mGLView);
    }
}
</pre>

<p class="note"><strong>Note:</strong> OpenGL ES 2.0 requires Android 2.2 (API Level 8) or higher,
so make sure your Android project targets that API or higher.</p>


<h2 id="glsurfaceview">Build a GLSurfaceView Object</h2>

<p>A {@link android.opengl.GLSurfaceView} is a specialized view where you can draw OpenGL ES
graphics.
It does not do much by itself. The actual drawing of objects is controlled in the {@link
android.opengl.GLSurfaceView.Renderer} that you set on this view. In fact, the code for this object
is so thin, you may be tempted to skip extending it and just create an unmodified {@link
android.opengl.GLSurfaceView} instance, but don’t do that. You need to extend this class in
order to capture touch events, which is covered in the <a href="#touch.html">Responding to Touch
Events</a> lesson.</p>

<p>The essential code for a {@link android.opengl.GLSurfaceView} is minimal, so for a quick
implementation, it is common to
just create an inner class in the activity that uses it:</p>

<pre>
class MyGLSurfaceView extends GLSurfaceView {

    private final MyGLRenderer mRenderer;

    public MyGLSurfaceView(Context context){
        super(context);

        // Create an OpenGL ES 2.0 context
        setEGLContextClientVersion(2);

        mRenderer = new MyGLRenderer();

        // Set the Renderer for drawing on the GLSurfaceView
        setRenderer(mRenderer);
    }
}
</pre>

<p>One other optional addition to your {@link android.opengl.GLSurfaceView} implementation is to set
the render mode to only draw the view when there is a change to your drawing data using the
{@link android.opengl.GLSurfaceView#RENDERMODE_WHEN_DIRTY GLSurfaceView.RENDERMODE_WHEN_DIRTY}
setting:</p>

<pre>
// Render the view only when there is a change in the drawing data
setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
</pre>

<p>This setting prevents the {@link android.opengl.GLSurfaceView} frame from being redrawn until you
call {@link android.opengl.GLSurfaceView#requestRender requestRender()}, which is more
efficient for this sample app.</p>


<h2 id="renderer">Build a Renderer Class</h2>

<p>The implementation of the {@link android.opengl.GLSurfaceView.Renderer} class, or renderer,
within an application that uses OpenGL ES is where things start to get interesting. This class
controls
what gets drawn on the {@link android.opengl.GLSurfaceView} with which it is associated. There are
three methods in a renderer that are called by the Android system in order to figure out what and
how to draw on a {@link android.opengl.GLSurfaceView}:</p>

<ul>
  <li>{@link android.opengl.GLSurfaceView.Renderer#onSurfaceCreated onSurfaceCreated()} -
Called once to set up the view's OpenGL ES environment.</li>
  <li>{@link android.opengl.GLSurfaceView.Renderer#onDrawFrame onDrawFrame()} - Called for each
redraw of the view.</li>
  <li>{@link android.opengl.GLSurfaceView.Renderer#onSurfaceChanged onSurfaceChanged()} - Called if
the geometry of the view changes, for example when the device's screen orientation changes.
  </li>
</ul>

<p>Here is a very basic implementation of an OpenGL ES renderer, that does nothing more than draw a
black background in the {@link android.opengl.GLSurfaceView}:</p>

<pre>
public class MyGLRenderer implements GLSurfaceView.Renderer {

    public void onSurfaceCreated(GL10 unused, EGLConfig config) {
        // Set the background frame color
        GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    }

    public void onDrawFrame(GL10 unused) {
        // Redraw background color
        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
    }

    public void onSurfaceChanged(GL10 unused, int width, int height) {
        GLES20.glViewport(0, 0, width, height);
    }
}
</pre>

<p>That’s all there is to it! The code examples above create a simple Android application that
displays a black screen using OpenGL. While this code does not do anything very interesting, by
creating these classes, you have laid the foundation you need to start drawing graphic elements with
OpenGL.</p>

<p class="note"><strong>Note:</strong> You may wonder why these methods have a {@link
javax.microedition.khronos.opengles.GL10} parameter, when you are using the OpengGL ES 2.0 APIs.
These method signatures are simply reused for the 2.0 APIs to keep the Android framework code
simpler.</p>

<p>If you are familiar with the OpenGL ES APIs, you should now be able to set up a OpenGL ES
environment in your app and start drawing graphics. However, if you need a bit more help getting
started with OpenGL, head on to the next lessons for a few more hints.</p>