adjusting screen brightness

ecume · 11-11-2008, 10:15 AM

I assume you need to jailbreak to get access to system controls like this, but I'll throw this out there in case someone has discovered a handy solution...

lapse · 11-11-2008, 10:36 AM

I believe the application 'Light' was removed from the store for messing with the screen brightness.

SkylarEC · 11-11-2008, 10:40 AM

Yes, Apple will reject your app if you mess with the brightness. Although, if you still want to do it, you'd get the current brightness like this:

Code:

-(void)getBacklightLevel;{
	NSNumber *bl = (NSNumber*) CFPreferencesCopyAppValue(CFSTR("SBBacklightLevel" ), CFSTR("com.apple.springboard"));
	 previousBacklightLevel = [bl floatValue]; //a variable to store the previous level so you can reset it.
	 [bl release];
}

And to set the backlight level, add this line

Code:

GSEventSetBacklightLevel(newLevel); //The new level: 0.0 - 1.0.

In order for this to work, you will need to include GraphicsServices.h. Depending on where you get your headers, you may need to add the GSEventSetBacklightLevel(float value); method to the headers, else the method won't quite work. [Some have reported kernel panics by not amending the header, but that has not been my experience]

wuf810 · 03-29-2009, 04:32 PM

Quote:

Originally Posted by SkylarEC

Yes, Apple will reject your app if you mess with the brightness. Although, if you still want to do it, you'd get the current brightness like this:

Code:

-(void)getBacklightLevel;{
	NSNumber *bl = (NSNumber*) CFPreferencesCopyAppValue(CFSTR("SBBacklightLevel" ), CFSTR("com.apple.springboard"));
	 previousBacklightLevel = [bl floatValue]; //a variable to store the previous level so you can reset it.
	 [bl release];
}

And to set the backlight level, add this line

Code:

GSEventSetBacklightLevel(newLevel); //The new level: 0.0 - 1.0.

In order for this to work, you will need to include GraphicsServices.h. Depending on where you get your headers, you may need to add the GSEventSetBacklightLevel(float value); method to the headers, else the method won't quite work. [Some have reported kernel panics by not amending the header, but that has not been my experience]

wow sorry to raise such as an old thread, but does anyone know if this still works. I can't seem to return the current backlight value anymore (I'm sure it worked once)....its for a private app BTW so no App store violations

TIA, Michael.

lewis · 05-01-2009, 09:13 PM

Quote:

Originally Posted by lapse

I believe the application 'Light' was removed from the store for messing with the screen brightness.

I've seen two applications ("Astronomy Flashlight" and "Flashlight.") in the store that adjust the screen's brightness one way or another. They probably don't adjust the system brightness but they seem to have a way to "dim" the screen. Any ideas? It appears possible if (at least) two apps have made it into the store.

arutad · 05-01-2009, 10:17 PM

Sneaky..!

Quote:

Originally Posted by SkylarEC

In order for this to work, you will need to include GraphicsServices.h. Depending on where you get your headers, you may need to add the GSEventSetBacklightLevel(float value); method to the headers, else the method won't quite work. [Some have reported kernel panics by not amending the header, but that has not been my experience]

ftm · 05-02-2009, 09:59 AM

I think Flashlight may just be using different color backgrounds... gray's appear dimmer than whites.

lewis · 05-02-2009, 12:16 PM

Quote:

Originally Posted by ftm

I think Flashlight may just be using different color backgrounds... gray's appear dimmer than whites.

Perhaps, but that doesn't explain how "Astronomy Flashlight" works and even if "Flashlight." does just use grays, how does it fade from one color to the gray?

wuf810 · 05-02-2009, 12:33 PM

Quote:

Originally Posted by lewis

Perhaps, but that doesn't explain how "Astronomy Flashlight" works and even if "Flashlight." does just use grays, how does it fade from one color to the gray?

they don't adjust the backlight levels...all they are doing is adjusting the alpha level of the top (red) view.

lewis · 05-03-2009, 03:38 PM

Quote:

Originally Posted by wuf810

they don't adjust the backlight levels...all they are doing is adjusting the alpha level of the top (red) view.

Oh, I see. Thanks.

So does anyone know how to find the GraphicsServices library? I know I won't be able to submit it to the App Store, but I can still use it personally, can't I? I located the GraphicsServices.framework (several, actually), but when I try and expand it there are no headers listed? Did Apple just remove access to this completely or is there something else that needs to be done? TIA.

wuf810 · 05-03-2009, 03:57 PM

Quote:

Originally Posted by lewis

Oh, I see. Thanks.

So does anyone know how to find the GraphicsServices library? I know I won't be able to submit it to the App Store, but I can still use it personally, can't I? I located the GraphicsServices.framework (several, actually), but when I try and expand it there are no headers listed? Did Apple just remove access to this completely or is there something else that needs to be done? TIA.

check out this link The iPhone SDK: APIs Apple Didn't Want You to Know About | O'Reilly Media

It has all the info you need but its quite complicated if you are new to this sort of stuff.

M.

Black Scyther · 09-25-2009, 09:19 AM

Sory for digging up this thread but i have a problem with that and hours of searching at google were unsuccessful.

Do I need to jailbreak my device to read the springboard.plist?

Code:

NSNumber *bl = (NSNumber*) CFPreferencesCopyAppValue(CFSTR("SBBacklightLevel" ), CFSTR("com.apple.springboard"));

bl is always nil on my device.

wuf810 · 09-25-2009, 11:13 AM

Quote:

Originally Posted by Black Scyther

Sory for digging up this thread but i have a problem with that and hours of searching at google were unsuccessful.

Do I need to jailbreak my device to read the springboard.plist?

Code:

NSNumber *bl = (NSNumber*) CFPreferencesCopyAppValue(CFSTR("SBBacklightLevel" ), CFSTR("com.apple.springboard"));

bl is always nil on my device.

This hasn't worked for me for a while. May have only worked in the early 2.x versions.

Not sure if anyone else has found another way to do it...

Black Scyther · 09-28-2009, 02:14 AM

Quote:

Originally Posted by wuf810

This hasn't worked for me for a while. May have only worked in the early 2.x versions.

Not sure if anyone else has found another way to do it...

Well, GSEventSetBacklightLevel works very well and i find it quite odd if there isn't any get method. But I can't find any in the classdump.

wuf810 · 09-28-2009, 05:08 AM

Quote:

Originally Posted by Black Scyther

Well, GSEventSetBacklightLevel works very well and i find it quite odd if there isn't any get method. But I can't find any in the classdump.

Yes confirmed. As you say setting the level works but trying to find the current level had changed.

Anyone?

Black Scyther · 10-21-2009, 03:51 AM

*push* Does anyone have a solution yet?

nir · 01-29-2011, 03:01 PM

Quote:

Originally Posted by Black Scyther

*push* Does anyone have a solution yet?

GSEventSetBacklightLevel works fine on 4.2. Didn't try getting the level.
There is another problem, though. Once I lock the phone and press the home button to use it again, the brightness is back to it's state before I changed it in my app.

Any way to save the changes so they'll last?

Thanx,
Nir.

Winmax · 02-26-2011, 03:05 PM

I'm also trying to get this working, but i have no success at all

all i get is this error:

Code:

 
"_GSEventSetBacklightLevel", referenced from:
-[MainViewController setBacklightLevel:] in MainViewController.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

Someone could give me a hint?

Greetings
Max

chenxintao · 04-16-2011, 10:08 PM

Quote:

Originally Posted by nir

GSEventSetBacklightLevel works fine on 4.2. Didn't try getting the level.
There is another problem, though. Once I lock the phone and press the home button to use it again, the brightness is back to it's state before I changed it in my app.

Any way to save the changes so they'll last?

Thanx,
Nir.

Hi,I want to use GSEventSetBacklightLevel, and I have #import "GraphicsServices.h", but there is a error. "_GSEventSetBacklightLevel", referenced from: .... symsbol not found.
And I can't find GraphicsServices.framework.How can I do to use GSEventSetBacklightLevel ?

Winmax · 04-17-2011, 06:27 AM

Quote:

Originally Posted by chenxintao

Hi,I want to use GSEventSetBacklightLevel, and I have #import "GraphicsServices.h", but there is a error. "_GSEventSetBacklightLevel", referenced from: .... symsbol not found.
And I can't find GraphicsServices.framework.How can I do to use GSEventSetBacklightLevel ?

Hi,
i Managed to get it working, maybe you/someday some else can find your/his solution with my code snip.

I used to change the backlight level with a UISlider, and programmatically with some "pulse" effect.

some vars needed in my code

Code:

	// init global vars
	_currentBacklightLevel = 0.2f;
	[self setBacklightLevel:_currentBacklightLevel];
	_pulseBacklightDirection = 0; // 0 = off, 1 = up, 2 = down

Creating my slider

Code:

	// create brightnessSlider
	brightnessSlider = [[UISlider alloc] initWithFrame:CGRectMake(18.0f, 420.0f, 258.0f, 23.0f)];
	[brightnessSlider addTarget:self action:@selector(brightnessSliderChanged:) forControlEvents:UIControlEventValueChanged];
	[brightnessSlider setBackgroundColor:[UIColor clearColor]];
	brightnessSlider.minimumValue = 0.0;
	brightnessSlider.maximumValue = 1.0;
	brightnessSlider.continuous = YES;
	brightnessSlider.value = _currentBacklightLevel;
	[self.view addSubview:brightnessSlider];

The main method, remember you won't pass appstore policy with this.

Code:

- (void)setBacklightLevel: (float)newLevel {[(id)[UIApplication sharedApplication] setBacklightLevel:newLevel]; // newLevel between 0.0f and 1.0f
}

My pulse function, just some little play i made

Code:

- (void)pulseBacklight {
		
	
	if (_pulseBacklightDirection > 0) {		
		if (_pulseBacklightDirection == 1) {
			if (_currentBacklightLevel < 0.975f) _currentBacklightLevel += 0.025f;
			else _pulseBacklightDirection = 2;
			
		}
		else if (_pulseBacklightDirection == 2) {
			if (_currentBacklightLevel > 0) _currentBacklightLevel -= 0.025f;
			else _pulseBacklightDirection = 1;
		}
		[self setBacklightLevel: _currentBacklightLevel];
		brightnessSlider.value = _currentBacklightLevel;
		[self performSelector:@selector(pulseBacklight) withObject:nil afterDelay:0.01f];
	}
	else {
		[self setBacklightLevel:0.5f];
		_currentBacklightLevel = 0.5f;
	}


}

Hope someday someone will see this, smile, and get his work done

Greetings
Max

RomanRobot · 08-23-2011, 02:54 PM

Quote:

Originally Posted by wuf810

they don't adjust the backlight levels...all they are doing is adjusting the alpha level of the top (red) view.

Hey I wanted to know. Since we're not allowed to tamper with the backlight, does dimming the screen by putting a black background and lowering the alpha of everything in front of it offer any energy savings? Anything close to lowering the backlight or not worth it? Does it actually cost more?

jimmyyjlee · 11-02-2011, 08:32 AM

where can i to get "GraphicsServices.h." this file ? thanks

Quote:

Originally Posted by SkylarEC

Yes, Apple will reject your app if you mess with the brightness. Although, if you still want to do it, you'd get the current brightness like this:

Code:

-(void)getBacklightLevel;{
	NSNumber *bl = (NSNumber*) CFPreferencesCopyAppValue(CFSTR("SBBacklightLevel" ), CFSTR("com.apple.springboard"));
	 previousBacklightLevel = [bl floatValue]; //a variable to store the previous level so you can reset it.
	 [bl release];
}

And to set the backlight level, add this line

Code:

GSEventSetBacklightLevel(newLevel); //The new level: 0.0 - 1.0.

In order for this to work, you will need to include GraphicsServices.h. Depending on where you get your headers, you may need to add the GSEventSetBacklightLevel(float value); method to the headers, else the method won't quite work. [Some have reported kernel panics by not amending the header, but that has not been my experience]