ну, это не точное решение, но оно послужит цели ...
-(IBAction)sliderValueChangedForBrightness:(UISlider*)sliderObj{
brightnessView.backgroundColor=[[UIColor grayColor] colorWithAlphaComponent:1-sliderObj.value];
}
-(IBAction)adjustBrightness:(UIButton *)sender{
if(isbrightnessViewShowing==NO){
isbrightnessViewShowing=YES;
[self.view addSubview:brightnessSliderView];
brightnessSliderView.frame=CGRectMake(sender.frame.origin.x-70,brandingView.frame.size.height, brightnessSliderView.frame.size.width, brightnessSliderView.frame.size.height);
}
else {
isbrightnessViewShowing=NO;
[brightnessSliderView removeFromSuperview];
}
if (brightnessView==nil) {
brightnessView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, scrollView.frame.size.width, scrollView.frame.size.height)];
brightnessView.backgroundColor = [UIColor clearColor];
}
[webView addSubview:brightnessView];
[webView bringSubviewToFront:brightnessView];
}