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[]{
 ,,, ,,, ,,, ,,, ,,,
 ,,, ,,, ,,, ,,, ,,,
 ,,, ,,, ,,, ,,, ,,,
 ,,, ,,, ,,, ,,, ,, };

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 * );
vbb.order(ByteOrder.nativeOrder());
vertexBuffer = vbb.asFloatBuffer();
vertexBuffer.put(vertices);
vertexBuffer.position();

ByteBuffer cbb
= ByteBuffer.allocateDirect(colors.length * );
cbb.order(ByteOrder.nativeOrder());
colorBuffer = cbb.asFloatBuffer();
colorBuffer.put(colors);
colorBuffer.position();

ByteBuffer ibb
= ByteBuffer.allocateDirect(indices.length * );
ibb.order(ByteOrder.nativeOrder());
indexBuffer = ibb.asShortBuffer();
indexBuffer.put(indices);
indexBuffer.position();

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(, , -);
 gl.glRotatef(angle, , , );

 gl.glFrontFace(GL10.GL_CCW);

 gl.glEnable(GL10.GL_CULL_FACE);

 gl.glCullFace(GL10.GL_BACK);

 gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);

 gl.glVertexPointer(, GL10.GL_FLOAT, , vertexBuffer);

 gl.glEnableClientState(GL10.GL_COLOR_ARRAY);

 gl.glColorPointer(, GL10.GL_FLOAT, , 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[]{
     ,,, ,,, ,,, ,,, ,,,
     ,,, ,,, ,,, ,,, ,,,
     ,,, ,,, ,,, ,,, ,,,
     ,,, ,,, ,,, ,,, ,, };
    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 * );
            vbb.order(ByteOrder.nativeOrder());
            vertexBuffer = vbb.asFloatBuffer();
            vertexBuffer.put(vertices);
            vertexBuffer.position();

            ByteBuffer cbb
            = ByteBuffer.allocateDirect(colors.length * );
            cbb.order(ByteOrder.nativeOrder());
            colorBuffer = cbb.asFloatBuffer();
            colorBuffer.put(colors);
            colorBuffer.position();

            ByteBuffer ibb
            = ByteBuffer.allocateDirect(indices.length * );
            ibb.order(ByteOrder.nativeOrder());
            indexBuffer = ibb.asShortBuffer();
            indexBuffer.put(indices);
            indexBuffer.position();

            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(, , -);

            float angle=;
            gl.glRotatef(angle, , , );

             gl.glFrontFace(GL10.GL_CCW);

             gl.glEnable(GL10.GL_CULL_FACE);

             gl.glCullFace(GL10.GL_BACK);

             gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);

             gl.glVertexPointer(, GL10.GL_FLOAT, , vertexBuffer);

             gl.glEnableClientState(GL10.GL_COLOR_ARRAY);

             gl.glColorPointer(, GL10.GL_FLOAT, , 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。