What is difference between QColor("transparent") and QColor(Qt::transparent)

Qt Enthusiast

Also

Why QColor(Qt::black) == QColor("transparent")

VRonin

qDebug() << "Qt::black" << QString::number(QColor(Qt::black).rgba(),16);
qDebug() << "transparent" << QString::number(QColor("transparent").rgba(),16);
qDebug() << "Qt::transparent" << QString::number(QColor(Qt::transparent).rgba(),16);
qDebug() << "Qt::black==transparent" << (QColor(Qt::black) == QColor("transparent"));

result:

Qt::black "ff000000"
transparent "0"
Qt::transparent "0"
Qt::black==transparent false

So:

What is difference between QColor("transparent") and QColor(Qt::transparent)

none

Why QColor(Qt::black) == QColor("transparent")

They are not

Qt Enthusiast

This post is deleted!

Qt Enthusiast

@VRonin

In 4.3.3 , I am getting following output
qDebug() << "Qt::black==transparent" << (QColor(Qt::black) == QColor("transparent"));

it is true

qDebug() << "Qt::transparent==transparent" << (QColor(Qt::transparent) == QColor("transparent")

as false

can u check

VRonin

That's probably because named colours did not support transparency until Qt 5.2, see https://bugreports.qt.io/browse/QTBUG-6725

QColor("transparent") in Qt 4 is actually fully opaque with RGB components all set to 0, in other words black

Qt Enthusiast

Can I consider to be bug of Qt.4.3.3

VRonin

not a bug, a feature

mrjj

@Qt-Enthusiast
Its not a bug. Its just how it worked back then. :)
You are using a very old Qt that is no longer maintained or change so in this case
its just how it was implemented back then. They later change it to support transparent in # syntax but
its not in your version.

Qt Enthusiast

What is signification of alpha value ?

QColor sc("transparent")

sc.alpha() is 255 for for qt.4.3.3
and
sc.alpha() is 0 after Qt 5.2

What is sc.alpha means

mrjj

@Qt-Enthusiast
alpha is the transparency level

VRonin

@Qt-Enthusiast said in What is difference between QColor("transparent") and QColor(Qt::transparent):

What is signification of alpha value ?

https://en.wikipedia.org/wiki/Alpha_compositing#Alpha_blending