aeroglass.c

#include <windows.h>
#include <stdio.h>
#include <psapi.h>

typedef BOOL (WINAPI *SetLayeredWindowAttributes_t) (HWND, COLORREF, BYTE, DWORD);
static SetLayeredWindowAttributes_t SetLayeredWindowAttributes;
static void changeWindowOpacity(HWND, float);
static BOOL CALLBACK onEnumWindow(HWND, LPARAM);
static const char *format = " %-4d  %-15s %s\n";
static const char *program_name;
static const char *image_name;
static double opacity;

void usage()
{
	printf("\
Usage: %s IMAGE OPACITY\n\
\n\
IMAGE     Name of the process image(s) whose windows' opacity is to be changed.\n\
OPACITY   Opacity value (0.0=invisible, 1.0=opaque)\n\
\n\
Change the opacity of visible Aero windows.\n\
", program_name);
}

int main(int argc, char **argv)
{
	program_name = "aeroglass"; // argv[0];

	if (1 == argc) {
		usage();
		return 0;
	}

	image_name = argv[1];
	opacity = argc > 2 ? atof(argv[2]) : 1.0;

	HMODULE User32DLL = LoadLibrary(TEXT("USER32.DLL"));

	if (!User32DLL) {
		printf("Could not load module `USER32.DLL.'\n"); 
		return 1;
	}

	SetLayeredWindowAttributes = (SetLayeredWindowAttributes_t) GetProcAddress(
		User32DLL, "SetLayeredWindowAttributes");

	printf(" PID  Image Name      Window Title\n");
	printf(" ---- --------------- ------------\n");

	if (!EnumWindows(onEnumWindow, 0)) {
		printf("Could not enumerate windows.\n");
		return 2;
	}

	FreeLibrary(User32DLL);

	return 0;
}

static BOOL CALLBACK onEnumWindow(HWND hwnd, LPARAM lparam)
{
	if (!IsWindowVisible(hwnd)) {
		return TRUE;
	}

	DWORD pid;
	GetWindowThreadProcessId(hwnd, &pid);

	HANDLE process = OpenProcess(PROCESS_QUERY_INFORMATION | PROCESS_VM_READ,
		FALSE, pid);

	if (!process) {
		return TRUE;
	}

	char process_name[MAX_PATH];
	GetModuleBaseName(process, NULL, process_name, sizeof(process_name));

	if (0 != strcmp(process_name, image_name)) {
		return TRUE;
	}

	changeWindowOpacity(hwnd, opacity);

	char text[MAX_PATH];
	GetWindowText(hwnd, text, sizeof(text));
	printf(format, pid, process_name, text);

	CloseHandle(process);

	return TRUE;
}

static void changeWindowOpacity(HWND hwnd, float opacity)
{
	SetWindowLong(hwnd, GWL_EXSTYLE,
		GetWindowLong(hwnd, GWL_EXSTYLE) | WS_EX_LAYERED);
	SetLayeredWindowAttributes(hwnd, RGB(128, 128, 128), 255 * opacity, 0x02);
}