Develop Reference

How to determine current AMOLED screen mode?

Many Android devices with AMOLED screens display all images with oversaturated colors by default. E.g. Samsung Galaxy phones have the "Adaptive" screen mode, which forces windows of all apps to be displayed as if they were rendered in the native screen color space, which is wider than Display-P3.
OTOH, not all such devices support EGL_EXT_gl_colorspace_display_p3, regardless of screen mode, so I can't be sure whether the device my app is running on even has a wide-gamut screen, even less determine whether this mode is the default.
So, how can I actually determine whether current screen mode is sRGB or some wide-gamut mode? I'm targeting one specific device model, Samsung Galaxy A320F/DS (AKA "A3 (2017)"), so platform-specific ways are also OK.

There are several layers where colors can be manipulated.
SurfaceFlinger. This component is common to all Android systems. One can pass a custom color matrix to it (see the source code of the handler of this request) via e.g. the following command executed as the root user:
service call SurfaceFlinger 1015 i32 1 \
f 0 f 0 f 1 f 0 \
f 0 f 1 f 0 f 0 \
f 1 f 0 f 0 f 0 \
f 0 f 0 f 0 f 1
The above example command sets a matrix that will, acting on RGBA vectors, swap red and blue channels. To reset the custom matrix to default (identity) you can simply do
service call SurfaceFlinger 1015 i32 0
You might be able to do all this from a Java/JNI app without root privileges, simply asking for some permission, I didn't research this.
mDNIe, which stands for mobile Digital Natural Image engine. It's a Samsung-specific system that acts on a lower level than SurfaceFlinger. Namely, it affects Always On Display, on which SurfaceFlinger's custom color matrix doesn't have any effect.
Current screen mode can be seen in the /sys/class/mdnie/mdnie/mode file, which appears to have the following mapping of values on Galaxy A320F/DS:
0 — AMOLED cinema (apparently aims at Display-P3),
1 — AMOLED photo (apparently aims at Adobe RGB),
2 — Basic (aims at sRGB),
3 — (don't know its purpose, but the value is accepted if written to mode)
4 — Adaptive display (the widest, apparently native screen color space).
5 — (don't know its purpose, but the value is accepted if written to mode)
Moreover, the colors are also affected by the Cool — Warm slider as well as Advanced options RGB per-channel adjustments. Changes to the former are somehow reflected in mdnie_ldu and sensorRGB files in the same directory, while the latter directly corresponds to whiteRGB file.
Also, Blue light filter feature state is reflected in the night_mode file (it also influences mdnie_ldu and sensorRGB files mentioned above).
Of the files described above, only mode is readable to a non-root user on SM-A320F/DS. On SM-G950FD (AKA "S8") nothing is accessible without root.

How to lock focus in camera2 api, android?

I am trying to lock focus after my custom camera finds focus.
First it AF mode set to auto:
builder.set(CaptureRequest.CONTROL_AF_MODE,
CaptureRequest.CONTROL_AF_MODE_AUTO);
And After touching the preview it finds focus distance, and I have to lock AF and AE using this code:
builder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
builder.set(CaptureRequest.CONTROL_AE_LOCK, true);
Locking AE works fine in any devices. Locking AF is working on Nexus5 and Nexus 5x. But as for Samsung S5 and S6, it keeps try to search focus.
What is the best way to lock focus?

In order to lock the AF you have to take care of requesting the AF_TRIGGER only once by using capture() instead of repeatingRequest() (if not it enters in an af request loop and remains always trying to focus, but some nexus fix this in its FW, so some devices as Nexus 5 focus well even it shouldn't)
So, the correct order will be:
Set CONTROL_AF_MODE to CONTROL_AF_MODE_AUTO (via session.setRepeatingRequest()) and the AF_REGIONS and the AE_REGIONS if you want
Wait until you check that the CONTROL_AF_MODE is already in auto by checking the totalCaptureRequest from the CaptureCallback.
Set the AF_TRIGGER_START in the builder along with the CONTROL_AF_MODE_AUTObut this time instead of using session.setRepeatingRequest() use session.capture().
Inmediately after that, set the AF_TRIGGER to set the AF_TRIGGER_IDLE (not cancel!) an use again session.setRepeatingRequest() along with the CONTROL_AF_MODE_AUTO.
Wait until it has focused,you will receive FOCUSED_LOCKED or NOT_FOCUSED_LOCKED.
The PASSIVE_FOCUSED state is only when the CONTROL_AF_MODE is in continuous picture not in auto!
Take care of being really in auto focus mode before performing the trigger.
You should use always session.capture() with all triggers (with CONTROL_AE_PRECAPTURE_TRIGGER too) but always after that remember to put the triggers to IDLE (not cancel) in a session.repeatingRequest()

You can't locus the focus on CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE.
You should put your AF mode on CONTROL_AF_MODE_AUTO adn wait for FOCUSED_LOCKED state during your AF trigger. You can check how the Android focus machine works on enter link description here

C++11 std::chrono::steady_clock issue on Android

I have been using std::chrono::steady_clock for interval calculation in an application i am making for Android platform.
Code:
// On application start
auto timeSinceEpoch = std::chrono::steady_clock::now().time_since_epoch();
auto timeInSec = std::chrono::duration_cast<seconds>(timeSinceEpoch).count();
log("On Enter Start Time Point - %lld", timeInSec);
Output:
On Enter Start Time Point - 521
Now i switch off the phone and restart the phone. I run my application and this time Output is:
On Enter Start Time Point - 114
As per definition at cppreference.com
"Class std::chrono::steady_clock represents a monotonic clock. The time points of this clock cannot decrease as physical time moves forward."
How is the output when i restart the phone giving lesser value?
If anyone has faced this issue please help me out here. Thanks!!

The formal requirement for a steady clock is that the result of a call to now() that happens before another call to now() is always less than or equal to the result of the second call. The happens before relationship only applies to actions within a program run. A steady clock is not required to be steady across different invocations of a program.

On Android, AFAICT steady_clock is the same as (from Java) System.Clock.elapsedRealtime, which resets to zero on boot -- https://developer.android.com/reference/android/os/SystemClock.html
I'm totally failing to dig up the source code for clock_gettime, though. https://android.googlesource.com/platform/ndk.git/+/43255f3d58b03cd931d29d1ee4e5144e86e875ce/sources/cxx-stl/llvm-libc++/libcxx/src/chrono.cpp#124 shows it calling clock_gettime(CLOCK_MONOTONIC), but I'm not sure how to penetrate the veil from there.

How to set brightness through ADB on nexus 7

I found some info on the web:
echo 1 /sys/devices/platform/flashlight.0/leds/flashlight/brightness
But on my Nexus 7 (flashed an AOSP), I couldn't find that directory.
Any idea about which file should I write to? Is this doable?
After ls /sys/devices/platform, I got:
LID
alarm
arm-pmu.0
bcm4330_rfkill
bcmdhd_wlan.1
bluesleep
fiq_debugger.0
fsl-tegra-udc
gpio-keys.0
grouper_misc
leds-gpio
oprofile-perf.0
power
power.0
pwm-backlight
ram_console
reg-dummy
reg-fixed-voltage.1
reg-fixed-voltage.10
reg-fixed-voltage.11
reg-fixed-voltage.2
reg-fixed-voltage.3
reg-fixed-voltage.4
reg-fixed-voltage.6
reg-fixed-voltage.8
regulatory.0
sdhci-tegra.2
sdhci-tegra.3
serial8250
snd-soc-dummy
spdif-dit.0
spdif-dit.1
spi_tegra.0
spi_tegra.3
tegra-ehci.1
tegra-i2c.0
tegra-i2c.1
tegra-i2c.2
tegra-i2c.3
tegra-i2c.4
tegra-nvmap
tegra-otg
tegra-pcm-audio
tegra-se
tegra-snd-rt5640.0
tegra30-ahub
tegra30-dam.0
tegra30-dam.1
tegra30-dam.2
tegra30-hda
tegra30-i2s.1
tegra30-i2s.3
tegra30-i2s.4
tegra30-spdif
tegra_camera
tegra_pwm.0
tegra_rtc
tegra_smmu
tegra_uart.1
tegra_uart.2
tegra_uart.3
tegra_uart.4
tegra_wdt
uevent

There is a new binary shipping with Android Jellybean 4.2, which can be used to directly read/write to the system settings provider, accessible via command line.
For example: in order to increase brightness of the screen, use below command:
adb shell settings put system screen_brightness 200
Read more about SCREEN_BRIGHTNESS Note that the range of values is [0 - 255]

The range of values is not necessarily from 0 - 255. On my OnePlus for example
it ranges from 0-2047. If you want to know yours just set the brightness slider to max and
then type: adb shell settings get system screen_brightness.

You should use the pwm-backlight!

You can use this adb command to set screen brightness
adb shell settings put system screen_brightness 255
and if your device has auto brightness setting then use this command first
adb shell settings put system screen_brightness_mode 0

This did not work for the latest Nexus 7 (2013) for me. But this answer explains the way to find what you are looking for on any version: https://stackoverflow.com/a/13492336
However we need to note that in order to change any of this you need to have root access.

Android - turn off hardware key lights

Inside my app, I need a way to turn off the lights on the standard Android phone keys (Home, Menu, Back, and Search) - how can I do this programmatically?

According to this page, the hardware key backlights can be controlled by writing to a specific file in the filesystem with superuser privileges (i.e. phone must be "rooted"):
Q: How can I control the keyboard
backlight?
A: The keyboard backlight can be
controlled via
/sys/class/leds/keyboard-backlight/brightness.
It appears that it's a simple on-off
control (echoing '0' turns it off,
echoing '1' or higher turns it on).
For some reason, the default system
backlight control stuff seems to set
this to "83", but I don't know why. I
can't seem to see any difference
between 83 and any other number. The
file is readable by anyone, but only
writable by root, so you'll need root
access to the phone to manipulate it
this way.
So to turn off the backlight programmatically, you could invoke exec() on the Runtime like so:
Runtime r = Runtime.getRuntime();
r.exec("echo 0 > /system/class/leds/keyboard-backlight/brightness");
Depends on what you are doing, but would probably be wise to check the result of exec() afterwards to see if a write error occurred.
Note: I tested this on my own phone and it seems to work without acting as root. However, this may not be the case on every phone, so you may have different results.

This is applicable only for the device samsung devices:
To get the BackLight sate:
int backLight = Settings.System.getInt(getContentResolver(), "button_key_light");
// if it return -1 it means that light is on
// if it return 0 the light is off
// some time it will return values like 600(1.5 sec)
if you want to put the backLight as off u can do like this
Settings.System.putInt(getApplicationContext().getContentResolver(), "button_key_light", 0);