QImage set transparency working but the initial form recovery don't

? Offline

Hello,

I drew an image using QPainter and I was trying to make it transparency. I was finally made it but now I would like to set the initial format. In fact I'm trying to do the inverse steps.

There's how I set the transparency:

@image = image.convertToFormat(QImage::Format_ARGB32);
image.fill(qRgba(0,0,0,0));@

Pradeep P N

Hi,

You can try with QPainter::CompositionMode. This might help you.

SGaist

Hi,

Something's not clear with your question. Do you mean you would like to start with:

@
QImage image(width, height, QImage::Format_ARGB32);
image.fill(Qt::transparent);
@

?

? Offline

From the start the image is normal displayed.

In paintEvent(QPaintEvent *event) I have:

@
QImage *img=new QImage(":/l4.png");
QImage image=img->scaled(64,64,Qt::IgnoreAspectRatio);
QPainter p;
p.begin(this);
QPointF newPoint;
newpoint.setX(10);
newpoint.setY(30);
p.drawImage(newpoint,image);@

I also have a button so when I clicked it the image dissapear (becomes transparent) as I supposed to do.

The slot is function void transparent():
@void MyProject::transparent()
{
image = image.convertToFormat(QImage::Format_ARGB32);
image.fill(qRgba(0,0,0,0));
}@

This does exactly what I want but now I have another button so when I clicked it I want to display the image;

raven-worx

so you want an "UNDO":http://doc.qt.io/qt-5/qundo.html function?
Anyway you would need to save the image and reset it.

SGaist

[quote author="Flavia" date="1422443422"]
@
QImage *img=new QImage(":/l4.png"); << Beware ! you have a memory leak
QImage image=img->scaled(64,64,Qt::IgnoreAspectRatio);
QPainter p;
p.begin(this);
QPointF newPoint;
newpoint.setX(10);
newpoint.setY(30);
p.drawImage(newpoint,image);
@
[/quote]

Beside the memory leak you are creating in your paint event, you are using a local variable named image and not your member variable of the same name.

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Yes, you're right! In fact I was declaring img and image in my header file class as public and instances in constructor. In paint event I have only:

@QPainter p;
p.begin(this);
QPointF newPoint;
newpoint.setX(10);
newpoint.setY(30);
p.drawImage(newpoint,image);@

I was in a rush of writing so I passed this fact in my previous post.
Thanks anyway for your suggestions and remarks!

SGaist

So you have it working as you want now ?

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Not yet but I was taking a look at QPainter::CompositionMode as Pradeep P N said and it seems to be the solution. I have not tested yet but the examples I found are exactly what I need.