摘要：
在中国找不到此代码。因此，参考相关代码后，以下代码是完整的，实现方法是通过IOCTL代码实现LCD背光调节功能。适用于平板电脑或笔记本电脑。这主要取决于BIOS是否支持它。
国内这种代码找不到。于是參考了相关代码后完好例如以下代码，且实现方式通过IOCTL代码实现LCD背光调节的功能。
适合场合为平板电脑或者笔记本。主要还是要靠BIOS支持与否。
编译环境使用：Dev-cpp工具编写。
#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
");
fprintf(stderr, "Usage: wbl.exe -b <level>
");
fprintf(stderr, " Option:
");
fprintf(stderr, " -b <level> brightness level need to be specified
");
fprintf(stderr, "
Error code:
");
fprintf(stderr, " Pass: 0; Fail: 1
");
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("
LCD 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("
Brightness_AC: %d
Brightness_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;
}