Automatic brightness control

[mgrouch]

Ideas:

OpenCPN/OpenCPN#2740

OpenCPN/OpenCPN#2427

https://github.com/jonls/redshift

[mgrouch]

See also pibright

from https://github.com/raspbian-addons/raspbian-addons

and
https://github.com/krishenriksen/pibright

[mgrouch]

Somehow pibright works under TwisterOS but doesn't work in BBN

TwisterOS settings:

pi@raspberrypi:~ $ lsmod
Module                  Size  Used by
cmac                   16384  1
rfcomm                 49152  16
bnep                   20480  2
hci_uart               40960  1
btbcm                  16384  1 hci_uart
bluetooth             393216  39 hci_uart,bnep,btbcm,rfcomm
ecdh_generic           16384  2 bluetooth
ecc                    40960  1 ecdh_generic
fuse                  126976  3
cdc_acm                24576  0
joydev                 20480  0
sg                     28672  0
hid_multitouch         24576  0
vc4                   253952  6
cec                    49152  1 vc4
brcmfmac              327680  0
v3d                    73728  7
drm_kms_helper        241664  3 vc4
gpu_sched              45056  1 v3d
brcmutil               20480  1 brcmfmac
sha256_generic         16384  0
cfg80211              761856  1 brcmfmac
rfkill                 32768  7 bluetooth,cfg80211
bcm2835_codec          36864  0
drm                   520192  17 v3d,vc4,gpu_sched,drm_kms_helper
bcm2835_isp            32768  0
v4l2_mem2mem           36864  1 bcm2835_codec
bcm2835_v4l2           40960  0
videobuf2_dma_contig    20480  2 bcm2835_isp,bcm2835_codec
bcm2835_mmal_vchiq     28672  3 bcm2835_isp,bcm2835_codec,bcm2835_v4l2
videobuf2_vmalloc      16384  1 bcm2835_v4l2
videobuf2_memops       16384  2 videobuf2_dma_contig,videobuf2_vmalloc
videobuf2_v4l2         32768  4 bcm2835_isp,bcm2835_codec,bcm2835_v4l2,v4l2_mem2mem
videobuf2_common       61440  5 bcm2835_isp,bcm2835_codec,bcm2835_v4l2,v4l2_mem2mem,videobuf2_v4l2
raspberrypi_hwmon      16384  0
videodev              249856  6 bcm2835_isp,bcm2835_codec,videobuf2_common,bcm2835_v4l2,v4l2_mem2mem,videobuf2_v4l2
mc                     45056  6 bcm2835_isp,bcm2835_codec,videobuf2_common,videodev,v4l2_mem2mem,videobuf2_v4l2
snd_bcm2835            28672  4
vc_sm_cma              32768  2 bcm2835_isp,bcm2835_mmal_vchiq
drm_panel_orientation_quirks    16384  1 drm
rpivid_mem             16384  0
snd_soc_core          225280  1 vc4
snd_compress           20480  1 snd_soc_core
snd_pcm_dmaengine      16384  1 snd_soc_core
snd_pcm               106496  5 snd_compress,vc4,snd_pcm_dmaengine,snd_bcm2835,snd_soc_core
snd_timer              32768  1 snd_pcm
snd                    77824  13 snd_compress,snd_timer,snd_bcm2835,snd_soc_core,snd_pcm
syscopyarea            16384  1 drm_kms_helper
nvmem_rmem             16384  0
sysfillrect            16384  1 drm_kms_helper
sysimgblt              16384  1 drm_kms_helper
fb_sys_fops            16384  1 drm_kms_helper
backlight              20480  1 drm
uio_pdrv_genirq        16384  0
uio                    20480  1 uio_pdrv_genirq
binfmt_misc            20480  1
ip_tables              28672  0
x_tables               32768  1 ip_tables
ipv6                  495616  44


pi@raspberrypi:~ $ cat /boot/config.txt 
# For more options and information see
# http://rpf.io/configtxt
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable infrared communication.
#dtoverlay=gpio-ir,gpio_pin=17
#dtoverlay=gpio-ir-tx,gpio_pin=18

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on

[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
dtoverlay=vc4-fkms-v3d
max_framebuffers=2

[all]
#dtoverlay=vc4-fkms-v3d
gpu_mem=128



pi@raspberrypi:~ $ cat /boot/cmdline.txt 
console=serial0,115200 console=tty1 root=PARTUUID=42dbb780-02 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait quiet splash plymouth.ignore-serial-consoles

pi@raspberrypi:~ $ tvservice -s
state 0xa [HDMI CUSTOM RGB full unknown AR], 1280x800 @ 60.00Hz, progressive

seems pibright works by modifying style CSS for Gtk3 dynamically

[mgrouch]

Some more docs

https://wiki.archlinux.org/title/backlight

rockowitz/ddcutil#356

Switching backlight off seems work on pi5 Bookworm

xset dpms force off

ddcutil will fail to set some VCP features if there is a feature enabled on the monitor which already automatically adjusts them (e.g. Dynamic Contrast Ratio or BenQ's Eye Care technology) or Auto Dodge.