1 page.title=Adding Motion 2 parent.title=Displaying Graphics with OpenGL ES 3 parent.link=index.html 4 5 trainingnavtop=true 6 previous.title=Applying Projection and Camera Views 7 previous.link=projection.html 8 next.title=Responding to Touch Events 9 next.link=touch.html 10 11 @jd:body 12 13 <div id="tb-wrapper"> 14 <div id="tb"> 15 16 <h2>This lesson teaches you to</h2> 17 <ol> 18 <li><a href="#rotate-gl1">Rotate a Shape</a></li> 19 <li><a href="#cont-render">Enable Continuous Rendering</a></li> 20 </ol> 21 22 <h2>You should also read</h2> 23 <ul> 24 <li><a href="{@docRoot}guide/topics/graphics/opengl.html">OpenGL</a></li> 25 </ul> 26 27 <div class="download-box"> 28 <a href="http://developer.android.com/shareables/training/OpenGLES.zip" 29 class="button">Download the sample</a> 30 <p class="filename">OpenGLES.zip</p> 31 </div> 32 33 </div> 34 </div> 35 36 <p>Drawing objects on screen is a pretty basic feature of OpenGL, but you can do this with other 37 Android graphics framwork classes, including {@link android.graphics.Canvas} and 38 {@link android.graphics.drawable.Drawable} objects. OpenGL ES provides additional capabilities for 39 moving and transforming drawn objects in three dimensions or in other unique ways to create 40 compelling user experiences.</p> 41 42 <p>In this lesson, you take another step forward into using OpenGL ES by learning how to add motion 43 to a shape with rotation.</p> 44 45 46 <h2 id="rotate">Rotate a Shape</h2> 47 48 <p>Rotating a drawing object with OpenGL ES 2.0 is relatively simple. You create another 49 transformation matrix (a rotation matrix) and then combine it with your projection and 50 camera view transformation matrices:</p> 51 52 <pre> 53 private float[] mRotationMatrix = new float[16]; 54 public void onDrawFrame(GL10 gl) { 55 ... 56 float[] scratch = new float[16]; 57 58 // Create a rotation transformation for the triangle 59 long time = SystemClock.uptimeMillis() % 4000L; 60 float angle = 0.090f * ((int) time); 61 Matrix.setRotateM(mRotationMatrix, 0, angle, 0, 0, -1.0f); 62 63 // Combine the rotation matrix with the projection and camera view 64 // Note that the mMVPMatrix factor *must be first* in order 65 // for the matrix multiplication product to be correct. 66 Matrix.multiplyMM(scratch, 0, mMVPMatrix, 0, mRotationMatrix, 0); 67 68 // Draw triangle 69 mTriangle.draw(scratch); 70 } 71 </pre> 72 73 <p>If your triangle does not rotate after making these changes, make sure you have commented out the 74 {@link android.opengl.GLSurfaceView#RENDERMODE_WHEN_DIRTY GLSurfaceView.RENDERMODE_WHEN_DIRTY} 75 setting, as described in the next section.</p> 76 77 78 <h2 id="cont-render">Enable Continuous Rendering</h2> 79 80 <p>If you have diligently followed along with the example code in this class to this point, make 81 sure you comment out the line that sets the render mode only draw when dirty, otherwise OpenGL 82 rotates the shape only one increment and then waits for a call to {@link 83 android.opengl.GLSurfaceView#requestRender requestRender()} from the {@link 84 android.opengl.GLSurfaceView} container:</p> 85 86 <pre> 87 public MyGLSurfaceView(Context context) { 88 ... 89 // Render the view only when there is a change in the drawing data. 90 // To allow the triangle to rotate automatically, this line is commented out: 91 <strong>//setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);</strong> 92 } 93 </pre> 94 95 <p>Unless you have objects changing without any user interaction, its usually a good idea have this 96 flag turned on. Be ready to uncomment this code, because the next lesson makes this call applicable 97 once again.</p> 98
