android 使用Java语言展示3D模型具体实现代码

以下是一个简单的使用Java语言展示3D模型的实现代码，其中使用了OpenGL ES 2.0和OBJ格式的模型文件：

public class MyGLRenderer implements GLSurfaceView.Renderer {
    private Context context;
    private ObjLoader objLoader;
    private int programId;
    private int positionHandle;
    private int normalHandle;
    private int textureHandle;
    private int modelMatrixHandle;
    private int viewMatrixHandle;
    private int projectionMatrixHandle;
    private int lightPositionHandle;
    private float[] modelMatrix = new float[16];
    private float[] viewMatrix = new float[16];
    private float[] projectionMatrix = new float[16];
    private float[] lightPosition = new float[]{0f, 0f, 0f};
    private float[] rotationMatrix = new float[16];
    private float[] translationMatrix = new float[16];
    private float[] scaleMatrix = new float[16];

    public MyGLRenderer(Context context) {
        this.context = context;
    }

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        // 加载OBJ文件
        objLoader = new ObjLoader(context);
        objLoader.loadObj("model.obj");

        // 编译顶点着色器和片段着色器
        int vertexShader = compileShader(GL_VERTEX_SHADER, vertexShaderCode);
        int fragmentShader = compileShader(GL_FRAGMENT_SHADER, fragmentShaderCode);

        // 连接顶点着色器和片段着色器，创建OpenGL程序
        programId = linkProgram(vertexShader, fragmentShader);

        // 获取变量句柄
        positionHandle = glGetAttribLocation(programId, "a_Position");
        normalHandle = glGetAttribLocation(programId, "a_Normal");
        textureHandle = glGetAttribLocation(programId, "a_TexCoord");
        modelMatrixHandle = glGetUniformLocation(programId, "u_ModelMatrix");
        viewMatrixHandle = glGetUniformLocation(programId, "u_ViewMatrix");
        projectionMatrixHandle = glGetUniformLocation(programId, "u_ProjectionMatrix");
        lightPositionHandle = glGetUniformLocation(programId, "u_LightPosition");

        // 启用深度测试
        glEnable(GL_DEPTH_TEST);
    }

    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height) {
        // 设置视口大小
        glViewport(0, 0, width, height);

        // 设置投影矩阵
        float ratio = (float) width / height;
        Matrix.frustumM(projectionMatrix, 0, -ratio, ratio, -1, 1, 1, 1000);
    }

    @Override
    public void onDrawFrame(GL10 gl) {
        // 清空屏幕和深度缓冲区
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // 使用OpenGL程序
        glUseProgram(programId);

        // 设置变换矩阵和光照位置
        Matrix.setIdentityM(modelMatrix, 0);
        Matrix.setIdentityM(rotationMatrix, 0);
        Matrix.setIdentityM(translationMatrix, 0);
        Matrix.setIdentityM(scaleMatrix, 0);
        Matrix.rotateM(rotationMatrix, 0, angle, 0, 1, 0);
        Matrix.translateM(translationMatrix, 0, 0, 0, -5);
        Matrix.scaleM(scaleMatrix, 0, 0.5f, 0.5f, 0.5f);
        Matrix.multiplyMM(modelMatrix, 0, translationMatrix, 0, modelMatrix, 0);
        Matrix.multiplyMM(modelMatrix, 0, rotationMatrix, 0, modelMatrix, 0);
        Matrix.multiplyMM(modelMatrix, 0, scaleMatrix, 0, modelMatrix, 0);
        glUniformMatrix4fv(modelMatrixHandle, 1, false, modelMatrix, 0);
        glUniformMatrix4fv(viewMatrixHandle, 1, false, viewMatrix, 0);
        glUniformMatrix4fv(projectionMatrixHandle, 1, false, projectionMatrix, 0);
        glUniform3fv(lightPositionHandle, 1, lightPosition, 0);

        // 绑定顶点属性
        objLoader.bindData(positionHandle, normalHandle, textureHandle);

        // 绘制模型
        glDrawArrays(GL_TRIANGLES, 0, objLoader.getPositions().size() / 3);
    }

    // 编译着色器
    private int compileShader(int type, String shaderCode) {
        int shaderId = glCreateShader(type);
        glShaderSource(shaderId, shaderCode);
        glCompileShader(shaderId);
        return shaderId;
    }

    // 连接着色器程序
    private int linkProgram(int vertexShaderId, int fragmentShaderId) {
        int programId = glCreateProgram();
        glAttachShader(programId, vertexShaderId);
        glAttachShader(programId, fragmentShaderId);
        glLinkProgram(programId);
        return programId;
    }
}

其中，vertexShaderCode和fragmentShaderCode分别是顶点着色器和片段着色器的代码。在Activity中，可以这样创建和注册GLSurfaceView：

public class MainActivity extends AppCompatActivity {
    private GLSurfaceView glSurfaceView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // 创建GLSurfaceView并设置Renderer
        glSurfaceView = new GLSurfaceView(this);
        glSurfaceView.setEGLContextClientVersion(2);
        glSurfaceView.setRenderer(new MyGLRenderer(this));

        // 将GLSurfaceView添加到布局中
        setContentView(glSurfaceView);
    }

    @Override
    protected void onResume() {
        super.onResume();
        glSurfaceView.onResume();
    }

    @Override
    protected void onPause() {
        super.onPause();
        glSurfaceView.onPause();
    }
}

在ObjLoader类中，可以使用OBJ文件解析库来加载模型文件，并将顶点、法线、纹理坐标等数据放入缓冲区中，供OpenGL ES绘制使用。