float[] vertexArray = new float[] {
   (float) -0.5, (float) -0.5, 0,
   (float) 0.5, (float) -0.5, 0,
   (float) -0.5, (float) 0.5, 0,
   (float) 0.5, (float) 0.5, 0
  };

public class Rectangle {
 private FloatBuffer mVertexBuffer;
 private int mProgram;
 private int mPositionHandle;

 public Rectangle(float r) {
  initVetexData(r);
 }

 public void initVetexData(float r) {
  // 初始化頂點(diǎn)坐標(biāo)
  float[] vertexArray = new float[] {
   (float) -0.5, (float) -0.5, 0,
   (float) 0.5, (float) -0.5, 0,
   (float) -0.5, (float) 0.5, 0,
   (float) 0.5, (float) 0.5, 0
  };

  ByteBuffer buffer = ByteBuffer.allocateDirect(vertexArray.length * 4);
  buffer.order(ByteOrder.nativeOrder());
  mVertexBuffer = buffer.asFloatBuffer();
  mVertexBuffer.put(vertexArray);
  mVertexBuffer.position(0);

  int vertexShader = loaderShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
  int fragmentShader = loaderShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);

  mProgram = GLES20.glCreateProgram();
  GLES20.glAttachShader(mProgram, vertexShader);
  GLES20.glAttachShader(mProgram, fragmentShader);
  GLES20.glLinkProgram(mProgram);

  mPositionHandle = GLES20.glGetAttribLocation(mProgram, "aPosition");
 }

 public void draw() {
  GLES20.glUseProgram(mProgram);
  // 將頂點(diǎn)數(shù)據(jù)傳遞到管線，頂點(diǎn)著色器
  GLES20.glVertexAttribPointer(mPositionHandle, 3, GLES20.GL_FLOAT, false, 0, mVertexBuffer);
  GLES20.glEnableVertexAttribArray(mPositionHandle);
  // 繪制圖元
  GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
 }

 private int loaderShader(int type, String shaderCode) {
  int shader = GLES20.glCreateShader(type);
  GLES20.glShaderSource(shader, shaderCode);
  GLES20.glCompileShader(shader);
  return shader;
 }

 private String vertexShaderCode = "attribute vec3 aPosition;"
   + "void main(){"
   + "gl_Position = vec4(aPosition,1);"
   + "}";

 private String fragmentShaderCode = "precision mediump float;"
   + "void main(){"
   + "gl_FragColor = vec4(1,0,0,0);"
   + "}";

}

public class RectangleView extends GLSurfaceView{

 public RectangleView(Context context) {
  super(context);
  setEGLContextClientVersion(2);
  setRenderer(new MyRender());
 }

 class MyRender implements GLSurfaceView.Renderer {
  private Rectangle rectangle;

  @Override
  public void onSurfaceCreated(GL10 gl, EGLConfig config) {
   GLES20.glClearColor(0.5f, 0.5f, 0.5f, 1);
   rectangle = new Rectangle(0.5f);
   GLES20.glEnable(GLES20.GL_DEPTH_TEST);
  }

  @Override
  public void onSurfaceChanged(GL10 gl, int width, int height) {
   GLES20.glViewport(0, 0, width, height);
  }

  @Override
  public void onDrawFrame(GL10 gl) {
   GLES20.glClear( GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);
   rectangle.draw();
  }
 }

}

public static void orthoM(float[] m, int mOffset,
  float left, float right, float bottom, float top,
  float near, float far)

@Override
  public void onSurfaceChanged(GL10 gl, int width, int height) {
   GLES20.glViewport(0, 0, width, height);
   // 根據(jù)屏幕方向設(shè)置投影矩陣
   float ratio= width > height ? (float)width / height : (float)height / width;
   if (width > height) {
    // 橫屏 
    Matrix.orthoM(mProjectionMatrix, 0, -ratio, ratio, -1, 1, 0, 5);
   } else {
    Matrix.orthoM(mProjectionMatrix, 0, -1, 1, -ratio, ratio, 0, 5);
   }
  }

private String vertexShaderCode = "uniform mat4 uProjectionMatrix;" // 增加這一行
   + "attribute vec3 aPosition;"
   + "void main(){"
   + "gl_Position = uProjectionMatrix * vec4(aPosition,1);" // 不是直接賦值而是乘以投影矩陣
   + "}";

 public static void setLookAtM(float[] rm, // 生成的攝像機(jī)矩陣
        int rmOffset,
   float eyeX, float eyeY, float eyeZ, // 攝像機(jī)的位置
   float centerX, float centerY, float centerZ, // 觀察目標(biāo)點(diǎn)的位置
               // 攝像機(jī)位置和觀察目標(biāo)點(diǎn)的位置確定了觀察方向
   float upX, float upY,float upZ // up向量在x、y、z軸上的分量，我覺(jué)得一般應(yīng)該是和觀察方向垂直的
        )

public static native void glViewport(
  int x,
  int y,
  int width,
  int height
 );