ybacklight

A program (and library) for managing the screen brightness.

A simpler alternative to xbacklight.

Building & Debugging

• Configure in config.h
• Build: make
• Test: make test
• Install: make install
• Build with debugging support: CFLAGS="-Og -g" make

Requirements

• Linux 2.4.10+ (or another sysfs compatible OS)
• A monitor with a software-controllable backlight (practically a laptop)

Installing

netsh -C "sudo make install" -c pixelcmtd/ybacklight

Usage

ybacklight [instruction-stream]

The instruction-stream contains a series of instructions.

ybacklight can be understood like a simple VM with four registers that we will call A, S, C and M here. A, C and M are long long (64 bit integer on sane compilers), S is a boolean value.

On startup, C is read as the current brightness value of the display and M from the maximal brightness value of the display, S is false and A -1.

Before exit, C is, if changed, written to the display's current brightness value and if any characters were written to stdout, a newline is written.

Instructions

• All numbers ([0-9]+) set the A register to their value, read in decimal
• S: sets the S register to true
• c: prints the C register to stdout
• m: prints the M register to stdout
• s: sets the C register to the value of the A register
• i: increments the C register by the value of the A register
• d: decrements the C register by the value of the A register
• All other instructions are just echoed

s, i and d can also be queued: If a number follows them directly, that is interpreted first.

You just need to understand one more constant: SHORT_FACTOR is defined in config.h, usually 100. All reads/writes from/to the C and M registers are divided/multiplied by SHORT_FACTOR, if the S register is set to true.

Examples

Examples have been merged into tldr (tldr ybacklight), so they are maintained there.

Using ybacklight as a library

If you want to, you can also use ybacklight.c as a library for reading and writing brightness values.

Give read_brightness the path of the brightness file to read from (e.g. /sys/class/backlight/intel_backlight/brightness) and it will yield the value.

Give write_brightness the path of the brightness file to write to and the value to write and it will write it.