前面介紹了OpenGL ES所有能夠繪制的基本圖形，點，線段和三角形。其它所有復雜的2D或3D圖形都是由這些基本圖形構成。

本例介紹如何使用三角形構造一個正20面體。一個正20面體，有12個頂點，20個面，30條邊構成：

創建一個DrawIcosahedron Activity， 定義20面體的12個頂點，和20個面如下：

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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 };

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OpenGL ES缺省使用同一種顏色來繪制圖形，為了能夠更好的顯示3D效果，我們為每個頂點隨機定義一些顏色如下：

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};

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將頂點，面，顏色存放到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);

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看一看DrawScene代碼：

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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++;}

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用來繪制20面體使用了gl.glDrawElements：

public abstract void glDrawElements(int mode, int count, int type, Buffer indices) ，可以重新定義頂點的順序，頂點的順序由indices Buffer 指定。

本例會顯示一個繞Y軸不斷旋轉的20面體，如何旋轉模型將在后面的坐標系統和坐標變換中介紹.

完整代碼：

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 Activityimplements 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. */@Overridepublic 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++;}@Overrideprotected void onResume() {// Ideally a game should implement// onResume() and onPause()// to take appropriate action when the//activity looses focus
            super.onResume();mGLSurfaceView.onResume();}@Overrideprotected void onPause() {// Ideally a game should implement onResume()//and onPause()// to take appropriate action when the//activity looses focus
            super.onPause();mGLSurfaceView.onPause();}}

其他類似。

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轉載于:https://www.cnblogs.com/Anita9002/p/4452612.html

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