为什么我清屏一句就花了20多毫秒啊……gl.glClear(GL10.GL_COLOR_BUFFER_BIT);求大神解答

@Override
public void onDrawFrame(GL10 gl)
{
long ks=System.currentTimeMillis();
gl.glClear(GL10.GL_COLOR_BUFFER_BIT);//清除颜色缓存和深度缓存
rndt=System.currentTimeMillis()-ks;
gl.glEnable(GL10.GL_CULL_FACE);//设置为打开背面剪裁
gl.glShadeModel(GL10.GL_SMOOTH);//设置着色模型为平滑着色
gl.glFrontFace(GL10.GL_CW);//设置逆时针为正
gl.glMatrixMode(GL10.GL_MODELVIEW);//设置当前矩阵为模式矩阵
gl.glLoadIdentity();//设置当前矩阵为单位矩阵
gl.glEnable(GL10.GL_BLEND);
//gl.glBlendFunc(GL10.GL_SRC_ALPHA,GL10.GL_ONE_MINUS_SRC_ALPHA);
gl.glBlendFunc(GL10.GL_ONE,GL10.GL_ONE_MINUS_SRC_ALPHA);
gl.glEnable(GL10.GL_LIGHTING);
gl.glEnable(GL10.GL_LIGHT0);
gl.glPushMatrix();
gl.glScalef(1,-1,1);
gl.glTranslatef(0,-Screen7e.fbly_raw,0);
Draw(gl);
gl.glPopMatrix();
}
public void Draw(GL10 gl){
}

public long rndt;
Brush br=new Brush();
@Override
public void onSurfaceCreated(GL10 gl, EGLConfig p2)
{
gl.glDisable(GL10.GL_DITHER);//关闭抗抖动
gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT,GL10.GL_FASTEST);//设置特定Hint项目的模式，这里为设置使用快速模式
gl.glClearColor(1,1,1,1);//设置屏幕背景色为黑色
gl.glDisable(GL10.GL_DEPTH_TEST);//启用深度检测
}
@Override
public void onSurfaceChanged(GL10 gl, int width, int height)
{
gl.glViewport(0, 0, width, height);
gl.glMatrixMode(GL10.GL_PROJECTION);
gl.glLoadIdentity();
gl.glOrthof(0,Screen7e.fblx_raw, 0, Screen7e.fbly_raw, 0, 1);
}