Use IOCTL code for LCD backlight Adjustment

Such Code cannot be found in China. Therefore, the following code is improved after the relevant code is referenced, and the implementation method uses IOCTL code to implement the LCD backlight adjustment function.

Suitable for tablets or laptops. It depends on BIOS support or not.

Compile the environment using the dev-CPP tool.

#include <stdio.h>#include <stdlib.h>#include <windows.h>#include <ddk/Ntddvdeo.h>typedef struct _DISPLAY_BRIGHTNESS {    UCHAR ucDisplayPolicy;    UCHAR ucACBrightness;    UCHAR ucDCBrightness;} DISPLAY_BRIGHTNESS, *PDISPLAY_BRIGHTNESS;#define IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS  CTL_CODE(FILE_DEVICE_VIDEO, 0x125, METHOD_BUFFERED, FILE_ANY_ACCESS)#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)void help(void){fprintf(stderr, "(c) Tody, 2014\n");fprintf(stderr, "Usage: wbl.exe -b <level>\n");fprintf(stderr, "  Option:\n");fprintf(stderr, "     -b <level>\t brightness level need to be specified\n");fprintf(stderr, "\n  Error code:\n");fprintf(stderr, "     Pass: 0;  Fail: 1\n");exit(1);}int setBrightness(int level){HANDLE h ;DWORD nOutBufferSize = 256;BYTE SupportedBrightness[256];DWORD g_supportedLevelCount; DISPLAY_BRIGHTNESS DisplayBrightness;memset(SupportedBrightness, 0, sizeof(SupportedBrightness));/* use createfile function to open lcd.  * url from microsoft about IOCTL code.*  http://msdn.microsoft.com/en-us/library/windows/desktop/aa372703%28v=vs.85%29.aspx*/h = CreateFile("\\\\.\\LCD", GENERIC_READ|GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, 0);if(h == INVALID_HANDLE_VALUE){printf("Open \\\\.\\LCD error");exit(1);}/* Query for display supported level */if(!DeviceIoControl(h, IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS, NULL, 0, SupportedBrightness, nOutBufferSize, &g_supportedLevelCount, NULL)){printf("IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS error - %d, - buffer: %d ", g_supportedLevelCount, nOutBufferSize);exit(1);}if (g_supportedLevelCount == 0)  /* 0 means not supported */{printf("\nLCD not support LEVEL COUNT", g_supportedLevelCount);exit(1);}DisplayBrightness.ucDisplayPolicy = 0;DisplayBrightness.ucACBrightness = level;DisplayBrightness.ucDCBrightness = level;/* Set display backlight level */nOutBufferSize = sizeof(DisplayBrightness);if(!DeviceIoControl(h, IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS, (DISPLAY_BRIGHTNESS *)&DisplayBrightness, nOutBufferSize, NULL, 0, &nOutBufferSize, NULL)){printf("IOCTL_VIDEO_SET_SUPPORTED_BRIGHTNESS error - %d, - buffer: %d ", g_supportedLevelCount, nOutBufferSize);exit(1);}Sleep(500); /* delay for some time while wmi event changed */nOutBufferSize = sizeof(DisplayBrightness);if(!DeviceIoControl(h, IOCTL_VIDEO_QUERY_DISPLAY_BRIGHTNESS, NULL, 0, (DISPLAY_BRIGHTNESS *)&DisplayBrightness, nOutBufferSize, &nOutBufferSize, NULL)){printf("IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS error - %d, - buffer: %d ", g_supportedLevelCount, nOutBufferSize);exit(1);}printf("\nBrightness_AC: %d\nBrightness_DC: %d", DisplayBrightness.ucACBrightness, DisplayBrightness.ucDCBrightness);}int main(int argc, char *argv[]) {/* program with arguments support */if (argc == 3 && strcmp("-b", argv[1])==0){setBrightness(atoi(argv[2]));}else{help();}return 0;}

Use IOCTL code for LCD backlight Adjustment