QPixmap change color every second

jrachman

In my application, I would like to take my QPixmap and change its color from green to yellow to red then back to green and continuous until the application is closed. Here is a Dropbox link to the code of the project: https://www.dropbox.com/s/s6mig7rfc2jiw6k/dummy.zip?dl=0. It contains 3 QPixmaps that need to be changing colors. Do not worry about the other text and stuff; all I want is the colors to be changing in real time. If there is a better method of real time color changing than QPixmaps, feel free to show me that as well.

Thank you.

mrjj

Hi
As far as i know, QImage is faster for image manipulation than QPixmap.
And you could offload the manipulation to a thread and only display in main.

But looking at the code, it seems you just want to draw a color rect on the QPixmap and not really change the color of the pixels ? or ?

jrachman

Hi mrjj,

Well I am not too familiar with this framework to answer you question but you seem right. I would like those 3 rectangles to change color whether it is drawing over the rectangle or changing the color of the pixels. Either way, they seem like they achieve my goal just in different ways.

mrjj

@jrachman
Yes and if small images, im not sure it matter much which you use.

jrachman

This post is deleted!

jrachman

@mrjj Ok, would you be able to provide me with a coding example or maybe edit one of the rectangles in my project?

SGaist

Hi,

QPixmap pixmap(100, 100);
pixmap.fill(Qt::red);

There you have a 100 by 100 red pixmap.

mrjj

Hi
do you mean you want to have a widget that flashes in red,green and yellow over and over?
like a led/lamp in some device ?

jrachman

@mrjj Ya like have the widget change colors every second.

jrachman

@SGaist How would I change the color every second?

SGaist

Using a QTimer and in the slot you update whatever widget you want to update. Since you're using a QPixmap, I guess you set it on a QLabel.

jrachman

@SGaist So make an update function?

SGaist

That method already exists for the widgets. Again, if you are using a QLabel to show the pixmap, then you can just set the new pixmap on the label.

jrachman

@SGaist Ok and what if I want the colors to change after a specific condition. For example, for int x, x<100, and x++, change the color to green if x%2==0 (else change color to red) then wait 5 seconds. @mrjj

mrjj

@jrachman
Hi
You can do all that in QTimers slot.
Say it calls your function every second.
You can then do something else after x seconds or keep track of
how many seconds passed since last time.

Do you need more than one of these "leds" in such case it would be easier to handle with a custom widget
as the housekeeping info would else have to live in mainwindow and could be messy for
more than a few flashing leds.

J.Hilk

Hi @jrachman

if I may suggest a different approach.

For me it seems, you should subclass QWidget, and overwrite the QWidget::paintEvent function.

Than you can use QPainter and draw directly on the Widget

something like:

void MyWidget::paintEvent(QPaintEvent *event)
{
    QWdiget::paintEvent(event);
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);
    QRect rect = QRect(290, 20, 70, 40);
    painter.fillRect(rect, Qt::red);
}

jrachman

@mrjj Hmmm... ya I am not too familiar with the QTimers slot stuff and how to make that work.

jrachman

@J.Hilk Ok I see. So would you be able to show me how you would implement this in with this example?: for int x, x<100, and x++, change the color to green if x%2==0 (else change color to red) then wait 5 seconds.

SGaist

You should then start by familiarising yourself with the Signals & Slots which is one of Qt's core feature.

As for your use case, you could also take advantage of QObject::startTimer which would avoid using signals and slots.