OpenGL ES 2.0：Square未显示（仅黑屏）

Question

我是OpenGL ES的新手，我正在尝试在我的Android应用程序中显示一个方块，但是当我运行应用程序时它只显示黑屏（没有方块）。谁能告诉我哪里出错了，请解决问题？

MainActivity.java

public class MainActivity extends AppCompatActivity {

private GLSurfaceView myGLSurfaceView;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    myGLSurfaceView = new GLSurfaceView(this);
    // Check if the system supports OpenGL ES 2.0.
    final ActivityManager activityManager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
    final ConfigurationInfo configurationInfo = activityManager.getDeviceConfigurationInfo();
    final boolean supportsEs2 = configurationInfo.reqGlEsVersion >= 0x20000;

    if (supportsEs2)
    {
        // Request an OpenGL ES 2.0 compatible context.
        myGLSurfaceView.setEGLContextClientVersion(2);

        // Set the renderer to our demo renderer, defined below.
        myGLSurfaceView.setRenderer(new MyRenderer());
    }
    else
    {
        // This is where you could create an OpenGL ES 1.x compatible
        // renderer if you wanted to support both ES 1 and ES 2.
        return;
    }
    setContentView(myGLSurfaceView);

}

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

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

MyRenderer.java

class MyRenderer implements GLSurfaceView.Renderer {

private Square mySq;
@Override
public void onSurfaceCreated(GL10 gl, EGLConfig config) {
    GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    mySq = new Square();

}

@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_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
    mySq.draw();
}

public static int loadShader(int type, String shaderCode){
    // create a vertex shader type (GLES20.GL_VERTEX_SHADER)
    // or a fragment shader type (GLES20.GL_FRAGMENT_SHADER)
    int shader = GLES20.glCreateShader(type);

    // add the source code to the shader and compile it
    GLES20.glShaderSource(shader, shaderCode);
    GLES20.glCompileShader(shader);

    return shader;
}
}

Square.java

public class Square {
    private FloatBuffer vertexBuffer;
    private ShortBuffer drawListBuffer;
    private final int mProgram;

    private int mPositionHandle;
    private int mColorHandle;
   // private final int vertexCount = squareCoords.length;
   private final int vertexCount =4;
    private final int vertexStride = Coords_per_vertex * 4;

    static final int Coords_per_vertex = 3;
    static float squareCoords[] = {
            -0.5f,  0.5f, 0.0f,   // top left
            -0.5f, -0.5f, 0.0f,   // bottom left
            0.5f, -0.5f, 0.0f,   // bottom right
            0.5f,  0.5f, 0.0f };  // top right

    float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 1.0f };

    private short drawOrder[]={0,1,2,0,2,3};

    private static final String vertexShaderCode = "attribute vec4 vPosition;" +
                                            "void main() {" +
                                                "gl_Position = vPosition;" +
                                            "}";

    private final String fragmentShaderCode = "precision mediump float;" +
                                               "uniform vec4 vColor;" +
                                             "void main() {" +
                                                "gl_Color = vColor;" +
                                              "}";


    public Square(){
        // initialize vertex byte buffer for shape coordinates
        ByteBuffer bb = ByteBuffer.allocateDirect(
                // (# of coordinate values * 4 bytes per float)
                squareCoords.length * 4);
        bb.order(ByteOrder.nativeOrder());
        vertexBuffer = bb.asFloatBuffer();
        vertexBuffer.put(squareCoords);
        vertexBuffer.position(0);

        // initialize byte buffer for the draw list
        ByteBuffer dlb = ByteBuffer.allocateDirect(
                // (# of coordinate values * 2 bytes per short)
                drawOrder.length * 2);
        dlb.order(ByteOrder.nativeOrder());
        drawListBuffer = dlb.asShortBuffer();
        drawListBuffer.put(drawOrder);
        drawListBuffer.position(0);

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

        // create empty OpenGL ES Program
        mProgram = GLES20.glCreateProgram();

        // add the vertex shader to program
        GLES20.glAttachShader(mProgram, vertexShader);

        // add the fragment shader to program
        GLES20.glAttachShader(mProgram, fragmentShader);

        // creates OpenGL ES program executables
        GLES20.glLinkProgram(mProgram);

        GLES20.glUseProgram(mProgram);


    }

    public void draw(){
        MyRenderer myR = new MyRenderer();
        mPositionHandle = GLES20.glGetAttribLocation(mProgram,"vPosition");
        GLES20.glEnableVertexAttribArray(mPositionHandle);
        GLES20.glVertexAttribPointer(mPositionHandle,Coords_per_vertex,GLES20.GL_FLOAT,false,vertexStride,vertexBuffer);

        mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");
        GLES20.glUniform4fv(mColorHandle,1,color,0);

        GLES20.glDrawArrays(GLES20.GL_TRIANGLES,0,vertexCount);
        // Disable vertex array
       // GLES20.glDisableVertexAttribArray(mPositionHandle);

    }

}