上一篇介绍了OpenGL ES能够绘制的几种基本几何图形:点,线,三角形。将分别介绍这几种基本几何图形的例子。为方便起见,暂时在同一平面上绘制这些几何图形,在后面介绍完OpenGL ES的坐标系统和坐标变换后,再介绍真正的3D图形绘制方法。
在Android OpenGL ES 开发教程(7):创建实例应用OpenGLDemos程序框架 创建了示例应用的程序框架,并提供了一个“Hello World?示例。
为避免一些重复代码,这里定义一个所有示例代码的基类OpenGLESActivity,其定义如下:
public class OpenGLESActivity extends Activity implements IOpenGLDemo{ /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); this.requestWindowFeature(Window.FEATURE_NO_TITLE); getWindow().setFlags( WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN); mGLSurfaceView = new GLSurfaceView(this); mGLSurfaceView.setRenderer(new OpenGLRenderer(this)); setContentView(mGLSurfaceView); } public void DrawScene(GL10 gl) { gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f); // Clears the screen and depth buffer. gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT); } @Override protected void onResume() { // Ideally a game should implement onResume() and onPause() // to take appropriate action when the activity looses focus super.onResume(); mGLSurfaceView.onResume(); } @Override protected void onPause() { // Ideally a game should implement onResume() and onPause() // to take appropriate action when the activity looses focus super.onPause(); mGLSurfaceView.onPause(); } protected GLSurfaceView mGLSurfaceView; }
OpenGL ES 内部存放图形数据的Buffer有COLOR ,DEPTH (深度信息)等,在绘制图形只前一般需要清空COLOR 和 DEPTH Buffer。
在屏幕上使用红色绘制3个点。创建一个DrawPoint 作为 OpenGLESActivity 的子类,并定义3个顶点的坐标:
public class DrawPoint extends OpenGLESActivity implements IOpenGLDemo{ float[] vertexArray = new float[]{ -0.8f , -0.4f * 1.732f , 0.0f , 0.8f , -0.4f * 1.732f , 0.0f , 0.0f , 0.4f * 1.732f , 0.0f , }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } ... }
下面为DrawPoint 的DrawScene 的实现:
public void DrawScene(GL10 gl) { super.DrawScene(gl); ByteBuffer vbb = ByteBuffer.allocateDirect(vertexArray.length*4); vbb.order(ByteOrder.nativeOrder()); FloatBuffer vertex = vbb.asFloatBuffer(); vertex.put(vertexArray); vertex.position(0); gl.glColor4f(1.0f, 0.0f, 0.0f, 1.0f); gl.glPointSize(8f); gl.glLoadIdentity(); gl.glTranslatef(0, 0, -4); gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertex); gl.glDrawArrays(GL10.GL_POINTS, 0, 3); gl.glDisableClientState(GL10.GL_VERTEX_ARRAY); }