Transparent Pixmap

[maverick_pol]

Hi,

I am currently working a bit with the QPixmap class. I am looking for a solution how to create a transparent pixmap. I need to create a QGraphicsPixmapItem and add it to the scene.
I am drawing different symbols( created from rects,polygons,lines <- describing shapes). For example, I would like to add 5 circles to the pixmap and only show those circles on the scene, as they were simple Items, not pixmaps.(in some cases these symbols will be much more complicated)
Transparency of a pixmap is the issue. By transparency I mean -> transparent background of the pixmap(no background). If I would not add anything to the pixmap and then painted it, nothing would be shown,etc.

Thank you for any help.

Kacper

[marcel]

Try:

pixmap.fill(Qt::Transparent);

pixmap.fill(Qt::Transparent);

To copy to clipboard, switch view to plain text mode 

but right after you open a painter on the pixmap, not before.

[maverick_pol]

Thanks.

Kacper

[maverick_pol]

Ok,

Is this code, what you mean?

QPixmap  world(100,100);
QPainter	painter(&world);
world.fill(Qt::transparent);
painter.setPen(Qt::black);
painter.setBrush(QBrush(Qt::black));
painter.drawRect(QRectF(QPointF(0,0),QPointF(50,50)));
iworld.save("C:/world.png","PNG");

QPixmap  world(100,100);
QPainter	painter(&world);
world.fill(Qt::transparent);
painter.setPen(Qt::black);
painter.setBrush(QBrush(Qt::black));
painter.drawRect(QRectF(QPointF(0,0),QPointF(50,50)));
iworld.save("C:/world.png","PNG");

To copy to clipboard, switch view to plain text mode 

while adding the "world.fill(Qt::transparent)" the whole pixmap is transparent(in the meaning of being empty)

What am I doing wrong or is there a flow in your answer?
I can set Brush as Qt::transparent and it fills the rect with no colors(that's ok), but what about the other part of the pixmap? I am currently looking for the answer.

Thanks for any further help.

Kacper

[EricF]

Ok,
while adding the "world.fill(Qt::transparent)" the whole pixmap is transparent(in the meaning of being empty)

What am I doing wrong or is there a flow in your answer?
I can set Brush as Qt::transparent and it fills the rect with no colors(that's ok), but what about the other part of the pixmap? I am currently looking for the answer.

Thanks for any further help.

Kacper

What do you mean by the whole pixmap is transparent, you don't see the rect you're drawing afterward ?

[maverick_pol]

I can't see anything. The whole pixmap is transparent, as if nothing been drawn.
world.png file and world2.png (the pixmap is filled with red):

[maverick_pol]

Ok, I suppose I have the solution:

....
QPixmap  world(100,100);
world.fill(Qt::transparent);
QPainter	painter(&world);
...

....
QPixmap  world(100,100);
world.fill(Qt::transparent);
QPainter	painter(&world);
...

To copy to clipboard, switch view to plain text mode 

..right after you open a painter on the pixmap, not before.

That was a bit misleading.

Thank you all for help.

Kacper