Backlight control for Android 4.2 in Qt project

[LeBol]

Hi.
We are porting our Qt application to Android platform. We made it basically working. However the remaining problem is a backlight control. Can anyone suggest a solution for such function.

[raven-worx]

@LeBol
not without using JNI and calling Android API.
You could subclass Qt's android activity and implement a method doing some JAVA stuff, like:

private void setBrightness(int brightness)  // brightness [0..100]
{
        Window w = getWindow();
        WindowManager.LayoutParams lp = w.getAttributes();
        lp.screenBrightness = (float)brightness/100.0;
        if (lp.screenBrightness<.01f) lp.screenBrightness=.01f;
        w.setAttributes(lp);
}

Then call this method via

jint brightness = 75;
QtAndroid::activity()->callMethod<void>("setBrightness", "(I)V", brightness);

Or the same JAVA code completely in C++ using QAndroidJniObjects (a bit more cumbersome).

Note: i haven't tested the JAVA code though.

[LeBol]

Thank you very much. We will try.

However, is there misspell here?
@raven-worx said in Backlight control for Android 4.2 in Qt project:

QtAndroid::activity()->callMethod<void>("setBrightness", "(I)V", brightness);

LeBol

[LeBol]

@raven-worx I am somewhat confused why the backlight value is converted to the range 0.01-1.0?
Is it not 0 -255?

[raven-worx]

@LeBol said in Backlight control for Android 4.2 in Qt project:

However, is there misspell here?

what exactly do you mean?

Is it not 0 -255?

https://developer.android.com/reference/android/view/WindowManager.LayoutParams.html#screenBrightness

[KroMignon]

@raven-worx said in Backlight control for Android 4.2 in Qt project:

private void setBrightness(int brightness) // brightness [0..100]

Looks good for me, but I think setBrightness() should be public not private!

[raven-worx]

@KroMignon said in Backlight control for Android 4.2 in Qt project:

Looks good for me, but I think setBrightness() should be public not private!

JNI doesn't care about visibility.

[LeBol]

@raven-worx
Thanks for the link regarding the backlight value range. I am total idiot with respect to Android API's.
'
However. What I meant by misspell.
I refer to your code you suggested earlier
QtAndroid::activity()->callMethod<void>("setBrightness", "(I)V", brightness);
Is this correct? There is no function activity() in QtAndroid namespace.

[raven-worx]

@LeBol said in Backlight control for Android 4.2 in Qt project:

Is this correct? There is no function activity() in QtAndroid namespace.

right. QtAndroid::androidActivity()

[LeBol]

@raven-worx
You've suggested to subclass AndroidActivity - in order to override setBrightness.

Don't we need to create a dynamic object (of this subclass) rather than calling the method statically?

[raven-worx]

@LeBol
in order for your code to be executed there must be already an activity up and running (the current instance is returned by QtAndroid::androidActivity()).
You need to specify your custom Activity class in the AndroidManifest.xml
No static methods involved (on the JAVA side)