backlight

/*
Copyright (c) 2016 Anonymous

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#include <stdlib.h>
#include <stdio.h>
#include <Windows.h>

typedef struct _DISPLAY_BRIGHTNESS {
    UCHAR ucDisplayPolicy;
    UCHAR ucACBrightness;
    UCHAR ucDCBrightness;
} DISPLAY_BRIGHTNESS, *PDISPLAY_BRIGHTNESS;

#define DISPLAYPOLICY_AC 0x00000001
#define DISPLAYPOLICY_DC 0x00000002
#define DISPLAYPOLICY_BOTH 0x00000003

#define IOCTL_VIDEO_QUERY_DISPLAY_BRIGHTNESS \
    CTL_CODE(FILE_DEVICE_VIDEO, 0x126, METHOD_BUFFERED, FILE_ANY_ACCESS)
#define IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS \
    CTL_CODE(FILE_DEVICE_VIDEO, 0x127, METHOD_BUFFERED, FILE_ANY_ACCESS)
#define IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS \
    CTL_CODE(FILE_DEVICE_VIDEO, 0x125, METHOD_BUFFERED, FILE_ANY_ACCESS)

void error(const wchar_t *where)
{
    wchar_t *msg = NULL;
    DWORD dw = GetLastError();
    if(FormatMessageW(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM
                      | FORMAT_MESSAGE_IGNORE_INSERTS,
                      NULL, dw, MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US),
                      (wchar_t *)&msg, 0, NULL) > 0)
    {
        fwprintf(stderr, L"Error in %ls: %ls", where, msg);
    }
    else
    {
        fwprintf(stderr, L"Error formatting error\n");
    }
    exit((int)dw);
}

HANDLE openLcd(void)
{
    HANDLE h = CreateFileW(L"\\\\.\\LCD", GENERIC_READ | GENERIC_WRITE,
                           FILE_SHARE_READ | FILE_SHARE_WRITE,
                           NULL, OPEN_EXISTING, 0, NULL);
    if(h == INVALID_HANDLE_VALUE)
    {
        error(L"CreateFileW");
    }
    return h;
}

int getSupported(HANDLE h, unsigned char *vals)
{
    size_t returned;
    if(DeviceIoControl(h, IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS, NULL, 0,
                       (LPVOID)vals, (DWORD)256, (LPDWORD)&returned, NULL) == 0)
    {
        error(L"IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS");
    }
    return returned;
}

DISPLAY_BRIGHTNESS getCurrent(HANDLE h)
{
    DISPLAY_BRIGHTNESS db;
    size_t returned;
    if(DeviceIoControl(h, IOCTL_VIDEO_QUERY_DISPLAY_BRIGHTNESS, NULL, 0,
                       (LPVOID)&db, (DWORD)sizeof(db), (LPDWORD)&returned, NULL) == 0
       || returned != sizeof(db))
    {
        error(L"IOCTL_VIDEO_QUERY_DISPLAY_BRIGHTNESS");
    }
    return db;
}

void setCurrent(HANDLE h, unsigned char val)
{
    DISPLAY_BRIGHTNESS db = getCurrent(h);
    size_t returned;
    if(db.ucDisplayPolicy == DISPLAYPOLICY_AC)
    {
        db.ucACBrightness = val;
    }
    else
    {
        db.ucDCBrightness = val;
    }
    if(DeviceIoControl(h, IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS, (LPVOID)&db, (DWORD)sizeof(db),
                       NULL, 0, (LPDWORD)&returned, NULL) == 0
       || returned != sizeof(db))
    {
        error(L"IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS");
    }
}

void queryFull(char *progname)
{
    int i;
    DISPLAY_BRIGHTNESS db;
    HANDLE h = openLcd();
    unsigned char vals[256];
    int count = getSupported(h, vals);
    printf("Supported brigtness values: ");
    for(i = 0; i < count; i++)
    {
        printf("%hhd ", vals[i]);
    }
    printf("\n");
    db = getCurrent(h);
    if(db.ucDisplayPolicy == DISPLAYPOLICY_AC)
    {
        printf("Current: AC power, brightness: %hhd, DC brigtness: %hhd\n",
               db.ucACBrightness, db.ucDCBrightness);
    }
    else
    {
        printf("Current: DC power, brightness: %hhd, AC brigtness: %hhd\n",
               db.ucDCBrightness, db.ucACBrightness);
    }
    printf("Use \"%s q\" to query current brightness, \"%s <value>\" to set current brightness\n",
           progname, progname);
}

unsigned char currentValue(DISPLAY_BRIGHTNESS db)
{
    if(db.ucDisplayPolicy == DISPLAYPOLICY_AC)
    {
        return db.ucACBrightness;
    }
    else
    {
        return db.ucDCBrightness;
    }
}

void query(void)
{
    HANDLE h = openLcd();
    DISPLAY_BRIGHTNESS db = getCurrent(h);
    printf("%hhd", currentValue(db));
}

void set(long value)
{
    int i;
    HANDLE h = openLcd();
    unsigned char vals[256];
    int count = getSupported(h, vals);
    int pos = 0;
    long min = value - vals[0];
    for(i = 1; i < count; i++)
    {
        if(value - vals[i] < min)
        {
            pos = i;
            min = value - vals[i];
        }
    }
    setCurrent(h, vals[pos]);
}

int main(int argc, char **argv)
{
    if(argc < 2)
    {
        queryFull(argv[0]);
    }
    else
    {
        if(argv[1][0] == 'q')
        {
            query();
        }
        else
        {
            char *c = argv[1];
            long val = strtol(c, &c, 10);
            if(c == argv[1])
            {
                queryFull(argv[0]);
            }
            else
            {
                set(val);
            }
        }
    }
    return 0;
}