为什么我的代码OpenGL android没有绘制三角形？

Question

为什么我的代码OpenGL android没有绘制三角形，我不知道为什么永远渲染黑屏的问题在哪里，有人可以帮我解决这个问题吗？

public class OpenGL implements GLSurfaceView.Renderer {

    int width,height;
    float blue = 0.f;

    @Override
    public void onDrawFrame(GL10 gl){

        gl.glClearColor(.0f,.0f,blue,0.f);
        gl.glClear(gl.GL_COLOR_BUFFER_BIT);

        float Vertex[] = {
                0.f, 1.f,
                1.f, -1.f,
                -1.f, -1.f,
        };

        ByteBuffer buffer;
        FloatBuffer _float;
        buffer = ByteBuffer.allocateDirect( Vertex.length * 4 );
        buffer.order( ByteOrder.nativeOrder() );
        _float = buffer.asFloatBuffer();
        _float.put( Vertex );
        _float.position(0);


        gl.glColor4f(1.f,1.f,0.f,1.f);
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);

        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, _float);
        gl.glDrawArrays(GL10.GL_TRIANGLES, 0, Vertex.length / 3);

        gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
    }

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig eglConfig) {

    }

    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height){
        this.width = width;
        this.height = height;

        gl.glViewport(0,0,width,height);

        gl.glMatrixMode(gl.GL_PROJECTION);
        gl.glLoadIdentity();
        gl.glOrthof(0,width,0,height,0,1);
        gl.glMatrixMode(gl.GL_MODELVIEW);
        gl.glLoadIdentity();
    }
}