Android OpenGL ES（十一）绘制一个20面体 .

2022-05-10 15:47:13

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。

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