阴影效果

    self.loginBtn.layer.shadowOffset = CGSizeMake(0, 0);
    self.loginBtn.layer.shadowColor = [UIColor redColor].CGColor;
    self.loginBtn.layer.shadowRadius = 150;
    self.loginBtn.layer.shadowOpacity = 1;

shadowOffset
偏移量
shadowColor
颜色
shadowRadius
阴影扩散的半径
shadowOpacity
阴影的透明度