setOpacity(0) doesn't fully work on masked QDialog

[umen]

Hi all
i try to set Opacity on masked QDialog but it doesn't fully set it
i still have the Main QDialog background color shown , it is masked with round corners
only the round corners get Opacity ..
here is the code it is in the paintEvent method :


QPainter painter(this);
painter.setRenderHints(QPainter::Antialiasing);
const QPalette& pal = palette();
float thickline = 1.5;//_sizes.thicker_line();
float border_rad = thickline * 4.0;
float w = width();
float h = height();
QImage mask_img(width(), height(), QImage::Format_Mono);
mask_img.fill(0xff);
QPainter mask_ptr(&mask_img);
mask_ptr.drawRoundedRect( QRectF( 0, 0, w, h),
border_rad+thickline/2.0,
border_rad+thickline/2.0 );

QBitmap bmp = QBitmap::fromImage(mask_img);
setMask( bmp );

QBrush bg_brush( pal.color(QPalette::Active, QPalette::Window) );
QPen border_pen( pal.color(QPalette::Active, QPalette::Dark) );
border_pen.setWidthF(thickline);
border_pen.setJoinStyle(Qt::RoundJoin);
painter.setPen(border_pen);
QRectF bg_rect = QRectF( thickline/2.0,
thickline/2.0,
w-thickline,
h-thickline );

painter.setBrush(bg_brush);

painter.setOpacity(0); <-----------------------------------HERE IS THE PROBLEMATIC CODE
mask_ptr.setOpacity(0);

mask_ptr.drawRoundedRect( QRectF( 0, 0, w, h),
border_rad+thickline/2.0,
border_rad+thickline/2.0 );

painter.drawRoundedRect( bg_rect,
border_rad,
border_rad );