Background for images with alpha channel

samkpo

I'm making an image viewer, and i have made it shows animated images, but i can't find the way to set the background for those that have an alpha channel. It's easy to make it with static images, using qpainter, but i don't know how to do it with animated images.

by the way, i'm learning both Qt and english, so please be patient :-P

vsorokin

Please, show you code, how you work with QMovie, and I don't understand you need "Alpha background" as in Title or "background for images with alpha channel" as in topic body? :)

dangelog

On a side note, QMovie is perfectly paintable with QPainter (you obtain the current frame with currentImage() or currentPixmap()).

samkpo

@QMovie movie = new QMovie (file->absoluteFilePath());
if (!movie->isValid()) {
qDebug()<<tr("Could not open %1 image").arg(file->absoluteFilePath());
return;
}

movie->start();
imageLabel->setMovie(movie);
imageLabel->resize(movie->scaledSize());@

that's the code.

how do you suggest i use QPainter?

vsorokin

imageLabel has type QLabel, right? QLabel is subclass of QWidget, QWidget is subclass of QPaintDevice.
Use QPainter for imageLabel

giesbert

So, I think Vass meant to overwrite "paintEvent":http://doc.qt.nokia.com/4.7/qwidget.html#paintEvent and do the painting by yourselve instead of let QImageLabel do the painting for you.

samkpo

yes, it's a QLabel Object. Ok, i understand what you say but don't know how to use QPainter for imageLabel

giesbert

If you do the painting on your own, you overwrite paint event like the following code:

@
void myWidgetClass::paintEvent(QPaintEvent*)
{
QPainter paint(this);
paint.drawImage(rect(), myMove.currentImage());
}
@

vsorokin

Gerolf It seems to me what I with you said about different things. As I understand samkpo has movie with alpha channel, and He want set background under this movie. You said about animate background for something with use Qmovie.

samkpo

yes, that's what i want

vsorokin

what exactly?

giesbert

Ok, sorry, then I misunderstood....

samkpo

i have a movie with alpha channel and i want to set a background under this movie

goetz

This code makes the background red. It's important to call setAutoFillBackground(true) on the label, otherwise the background will not be changed!

@
QPalette pal = ui->label->palette();
pal.setBrush(QPalette::Window, Qt::red);
ui->label->setPalette(pal);
ui->label->setAutoFillBackground(true);
@

dangelog

You need to subclass QLabel (or simply write a new widget from scratch) and in its paintEvent paint the background and then the current QMovie frame; or you can enable autoFillBackground and change the label's background palette. :)

giesbert

bq. Vass wrote
Gerolf It seems to me what I with you said about different things. As I understand samkpo has movie with alpha channel, and He want set background under this movie. You said about animate background for something with use Qmovie.

But then you can just paint the background beffore drawing the move:

@
void myWidgetClass::paintEvent(QPaintEvent*)
{
QPainter paint(this);
painter.draw... // draw the background here
paint.drawImage(rect(), myMove.currentImage());
}
@

Or position a label or widget with the needed background exactly below the imageLabel. (so position one widget with setgeometry or make obne label a child of the other one). Or does QLabel not draw the movie with transparent background?

goetz

Gerolf, ok, there's always more than one way to achieve things, but setting the background palette and autoFillBackground should be enough in this case :-)

vsorokin

Gerolf I don't know, I think what enough lay one widget under this. Or you are right, call set background before current frame paint.

samkpo

nop, the palette stuff didn't work, when i call setMovie the background is gone, and even calling setBackgroundColor from QMovie doesn't work, so i've done something that fixes my problem, but in a way that isn't the better i guess.

@void ImageViewer::setGifImage()
{
QPixmap m = scuareBackground();
//m is an square 32x32, wich is the base for the alpha background.

QPixmap temp(gifSize);
//create a pixmap qith the same size that the gif image

QPainter q(&temp);
q.drawTiledPixmap(0,0,gifSize.width(), gifSize.height(), m);
q.drawPixmap(0, 0, movie->currentPixmap());
q.end();

imageLabel->setPixmap(temp);
}
@

that's an slot i've made, and it's used in here:

@gifSize=(QPixmap(archivo->absoluteFilePath()).size());

movie->start();
connect(movie, SIGNAL(frameChanged(int)), this, SLOT(setGifImage()));

//imageLabel->setMovie(movie);
imageLabel->resize(gifSize);@

of course i have to make a lot of improvements but it's something.

if you have something to add or correct do it please

goetz

Setting background color via palette works for me. I don't know if you want to set only a background color or a background image. The latter would be harder to achieve.