Android OpenGL ES（十一）绘制一个20面体 .
前面介绍了OpenGL ES所有能够绘制的基本图形，点，线段和三角形。其它所有复杂的2D或3D图形都是由这些基本图形构成。
本例介绍如何使用三角形构造一个正20面体。一个正20面体，有12个顶点，20个面，30条边构成：
创建一个DrawIcosahedron Activity， 定义20面体的12个顶点，和20个面如下：
static final float X=.525731112119133606f; static final float Z=.850650808352039932f; static float vertices[] = new float[]{ -X, 0.0f, Z, X, 0.0f, Z, -X, 0.0f, -Z, X, 0.0f, -Z, 0.0f, Z, X, 0.0f, Z, -X, 0.0f, -Z, X, 0.0f, -Z, -X, Z, X, 0.0f, -Z, X, 0.0f, Z, -X, 0.0f, -Z, -X, 0.0f }; static short indices[] = new short[]{ 0,4,1, 0,9,4, 9,5,4, 4,5,8, 4,8,1, 8,10,1, 8,3,10, 5,3,8, 5,2,3, 2,7,3, 7,10,3, 7,6,10, 7,11,6, 11,0,6, 0,1,6, 6,1,10, 9,0,11, 9,11,2, 9,2,5, 7,2,11 };
OpenGL ES缺省使用同一种颜色来绘制图形，为了能够更好的显示3D效果，我们为每个顶点随机定义一些颜色如下：
float[] colors = { 0f, 0f, 0f, 1f, 0f, 0f, 1f, 1f, 0f, 1f, 0f, 1f, 0f, 1f, 1f, 1f, 1f, 0f, 0f, 1f, 1f, 0f, 1f, 1f, 1f, 1f, 0f, 1f, 1f, 1f, 1f, 1f, 1f, 0f, 0f, 1f, 0f, 1f, 0f, 1f, 0f, 0f, 1f, 1f, 1f, 0f, 1f, 1f };
将顶点，面，颜色存放到Buffer中以提高性能：
private FloatBuffer vertexBuffer; private FloatBuffer colorBuffer; private ShortBuffer indexBuffer; ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length * 4); vbb.order(ByteOrder.nativeOrder()); vertexBuffer = vbb.asFloatBuffer(); vertexBuffer.put(vertices); vertexBuffer.position(0); ByteBuffer cbb = ByteBuffer.allocateDirect(colors.length * 4); cbb.order(ByteOrder.nativeOrder()); colorBuffer = cbb.asFloatBuffer(); colorBuffer.put(colors); colorBuffer.position(0); ByteBuffer ibb = ByteBuffer.allocateDirect(indices.length * 2); ibb.order(ByteOrder.nativeOrder()); indexBuffer = ibb.asShortBuffer(); indexBuffer.put(indices); indexBuffer.position(0);
看一看DrawScene代码：
public void DrawScene(GL10 gl) { super.DrawScene(gl); gl.glColor4f(1.0f, 0.0f, 0.0f, 1.0f); gl.glLoadIdentity(); gl.glTranslatef(0, 0, -4); gl.glRotatef(angle, 0, 1, 0); gl.glFrontFace(GL10.GL_CCW); gl.glEnable(GL10.GL_CULL_FACE); gl.glCullFace(GL10.GL_BACK); gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer); gl.glEnableClientState(GL10.GL_COLOR_ARRAY); gl.glColorPointer(4, GL10.GL_FLOAT, 0, colorBuffer); gl.glDrawElements(GL10.GL_TRIANGLES, indices.length, GL10.GL_UNSIGNED_SHORT, indexBuffer); gl.glDisableClientState(GL10.GL_VERTEX_ARRAY); gl.glDisable(GL10.GL_CULL_FACE); angle++; }
用来绘制20面体使用了gl.glDrawElements：
public abstract void glDrawElements(int mode, int count, int type, Buffer indices) ，可以重新定义顶点的顺序，顶点的顺序由indices Buffer 指定。
本例会显示一个绕Y轴不断旋转的20面体，如何旋转模型将在后面的坐标系统和坐标变换中介绍.
完整代码：
MainActiviy.java
package com.example.gltest; import java.nio.ByteBuffer; import java.nio.ByteOrder; import java.nio.FloatBuffer; import java.nio.ShortBuffer; import javax.microedition.khronos.opengles.GL10; import android.opengl.GLSurfaceView; import android.os.Bundle; import android.app.Activity; import android.view.Menu; import android.view.Window; import android.view.WindowManager; public class MainActivity extends Activity implements IOpenGLDemo{ private FloatBuffer vertexBuffer; private FloatBuffer colorBuffer; private ShortBuffer indexBuffer; private GLSurfaceView mGLSurfaceView; static final float X=.525731112119133606f; static final float Z=.850650808352039932f; static float vertices[] = new float[]{ -X, 0.0f, Z, X, 0.0f, Z, -X, 0.0f, -Z, X, 0.0f, -Z, 0.0f, Z, X, 0.0f, Z, -X, 0.0f, -Z, X, 0.0f, -Z, -X, Z, X, 0.0f, -Z, X, 0.0f, Z, -X, 0.0f, -Z, -X, 0.0f }; static short indices[] = new short[]{ 0,4,1, 0,9,4, 9,5,4, 4,5,8, 4,8,1, 8,10,1, 8,3,10, 5,3,8, 5,2,3, 2,7,3, 7,10,3, 7,6,10, 7,11,6, 11,0,6, 0,1,6, 6,1,10, 9,0,11, 9,11,2, 9,2,5, 7,2,11 }; float[] colors = { 0f, 0f, 0f, 1f, 0f, 0f, 1f, 1f, 0f, 1f, 0f, 1f, 0f, 1f, 1f, 1f, 1f, 0f, 0f, 1f, 1f, 0f, 1f, 1f, 1f, 1f, 0f, 1f, 1f, 1f, 1f, 1f, 1f, 0f, 0f, 1f, 0f, 1f, 0f, 1f, 0f, 0f, 1f, 1f, 1f, 0f, 1f, 1f }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length * 4); vbb.order(ByteOrder.nativeOrder()); vertexBuffer = vbb.asFloatBuffer(); vertexBuffer.put(vertices); vertexBuffer.position(0); ByteBuffer cbb = ByteBuffer.allocateDirect(colors.length * 4); cbb.order(ByteOrder.nativeOrder()); colorBuffer = cbb.asFloatBuffer(); colorBuffer.put(colors); colorBuffer.position(0); ByteBuffer ibb = ByteBuffer.allocateDirect(indices.length * 2); ibb.order(ByteOrder.nativeOrder()); indexBuffer = ibb.asShortBuffer(); indexBuffer.put(indices); indexBuffer.position(0); 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(1.0f, 0.0f, 0.0f, 0.0f); // // Clears the screen and depth buffer. // gl.glClear(GL10.GL_COLOR_BUFFER_BIT // | GL10.GL_DEPTH_BUFFER_BIT); // // } public void DrawScene(GL10 gl) { // super.DrawScene(gl); gl.glColor4f(1.0f, 0.0f, 0.0f, 1.0f); gl.glLoadIdentity(); gl.glTranslatef(0, 0, -4); float angle=0; gl.glRotatef(angle, 0, 1, 0); gl.glFrontFace(GL10.GL_CCW); gl.glEnable(GL10.GL_CULL_FACE); gl.glCullFace(GL10.GL_BACK); gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer); gl.glEnableClientState(GL10.GL_COLOR_ARRAY); gl.glColorPointer(4, GL10.GL_FLOAT, 0, colorBuffer); gl.glDrawElements(GL10.GL_TRIANGLES, indices.length, GL10.GL_UNSIGNED_SHORT, indexBuffer); gl.glDisableClientState(GL10.GL_VERTEX_ARRAY); gl.glDisable(GL10.GL_CULL_FACE); angle++; } @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(); } }
其他类似。
