physical dots per inch in a .pragma library

Hi,
my project relies heavily on QtQuick and is supposed to work on very different screen sizes.
To have reasonable sizes of my items, I import this .js file into every qml document:

Code:

---

function dp(dpVal) {
    var px = Math.round(dpVal * (screenPixelDensity *0.00625 )); // 1 * 0.00625 === 1 / 160
    if(Qt.platform.os == "windows" || Qt.platform.os == "mac") {
        return px*2;
    } else {
        return px;
    }
}

---

I can then use it similar to absolute values:

Code:

---

width: Geo.dp(50)

---

"screenPixelDensity" is set as a context property by c++:

Code:

---

m_engine.rootContext()->setContextProperty("screenPixelDensity", QGuiApplication::primaryScreen()->physicalDotsPerInch());

---

Now, if I understand correctly, by using import, this .js is being copied into each .qml file insead of using one instance. So I've tried to define it as a .pragma library.
Unfortunately, I cannot access screenPixelDensity (or any other QML varable) from the .js if I do so.

Is there a possibility to access the screen pixel density value from within js?

Since this calculation is based on two values from C++, the physical dots per inch and the platform, my suggestion would be to just move the function to C++ as well.

It could even do the OS lookup just once, or not all all and decide the factor at compile time.

Cheers,
_

Interesting idea! This solution is located outside my former box of thinking :-)

Sounds perfectly reasonable to do it in C++. I'm not sure of the speed penalty (it' not necessarily a constant , at runtime the user might change screen resolution), of but calling a c++ INVOKABLE shouldn't be worse than calling a js, I guess. Thank you!

I also wasn't actually aware that Qt.platform.os is a C++ thing. Good to know! Cheers!!