| page.title=Adding Motion |
| parent.title=Displaying Graphics with OpenGL ES |
| parent.link=index.html |
| |
| trainingnavtop=true |
| previous.title=Applying Projection and Camera Views |
| previous.link=projection.html |
| next.title=Responding to Touch Events |
| next.link=touch.html |
| |
| @jd:body |
| |
| <div id="tb-wrapper"> |
| <div id="tb"> |
| |
| <h2>This lesson teaches you to</h2> |
| <ol> |
| <li><a href="#rotate-gl1">Rotate a Shape</a></li> |
| <li><a href="#cont-render">Enable Continuous Rendering</a></li> |
| </ol> |
| |
| <h2>You should also read</h2> |
| <ul> |
| <li><a href="{@docRoot}guide/topics/graphics/opengl.html">OpenGL</a></li> |
| </ul> |
| |
| <div class="download-box"> |
| <a href="http://developer.android.com/shareables/training/OpenGLES.zip" |
| class="button">Download the sample</a> |
| <p class="filename">OpenGLES.zip</p> |
| </div> |
| |
| </div> |
| </div> |
| |
| <p>Drawing objects on screen is a pretty basic feature of OpenGL, but you can do this with other |
| Android graphics framwork classes, including {@link android.graphics.Canvas} and |
| {@link android.graphics.drawable.Drawable} objects. OpenGL ES provides additional capabilities for |
| moving and transforming drawn objects in three dimensions or in other unique ways to create |
| compelling user experiences.</p> |
| |
| <p>In this lesson, you take another step forward into using OpenGL ES by learning how to add motion |
| to a shape with rotation.</p> |
| |
| |
| <h2 id="rotate">Rotate a Shape</h2> |
| |
| <p>Rotating a drawing object with OpenGL ES 2.0 is relatively simple. You create another |
| transformation matrix (a rotation matrix) and then combine it with your projection and |
| camera view transformation matrices:</p> |
| |
| <pre> |
| private float[] mRotationMatrix = new float[16]; |
| public void onDrawFrame(GL10 gl) { |
| ... |
| // Create a rotation transformation for the triangle |
| long time = SystemClock.uptimeMillis() % 4000L; |
| float angle = 0.090f * ((int) time); |
| Matrix.setRotateM(mRotationMatrix, 0, angle, 0, 0, -1.0f); |
| |
| // Combine the rotation matrix with the projection and camera view |
| Matrix.multiplyMM(mMVPMatrix, 0, mRotationMatrix, 0, mMVPMatrix, 0); |
| |
| // Draw triangle |
| mTriangle.draw(mMVPMatrix); |
| } |
| </pre> |
| |
| <p>If your triangle does not rotate after making these changes, make sure you have commented out the |
| {@link android.opengl.GLSurfaceView#RENDERMODE_WHEN_DIRTY GLSurfaceView.RENDERMODE_WHEN_DIRTY} |
| setting, as described in the next section.</p> |
| |
| |
| <h2 id="cont-render">Enable Continuous Rendering</h2> |
| |
| <p>If you have diligently followed along with the example code in this class to this point, make |
| sure you comment out the line that sets the render mode only draw when dirty, otherwise OpenGL |
| rotates the shape only one increment and then waits for a call to {@link |
| android.opengl.GLSurfaceView#requestRender requestRender()} from the {@link |
| android.opengl.GLSurfaceView} container:</p> |
| |
| <pre> |
| public MyGLSurfaceView(Context context) { |
| ... |
| // Render the view only when there is a change in the drawing data |
| //setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY); // comment out for auto-rotation |
| } |
| </pre> |
| |
| <p>Unless you have objects changing without any user interaction, it’s usually a good idea have this |
| flag turned on. Be ready to uncomment this code, because the next lesson makes this call applicable |
| once again.</p> |