initial

Author: ftk

.gitattributes

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+# Auto detect text files and perform LF normalization
+* text=auto

Makefile

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+
+# compile without c runtime library to make binary super small (~3k)
+kbled.exe: kbled2.c
+	gcc -Dmain=mainCRTStartup -std=c11 -nostdlib -mwindows $< -o $@ -luser32 -lkernel32 -Ofast -march=native -s -fvisibility=hidden -fno-ident

kbled.c

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+#include <windows.h>
+#include <stdbool.h>
+
+static const int vkey_scroll = 0x91,
+        scan_scroll = 0x46;
+
+static void press_scroll()
+{
+        keybd_event(vkey_scroll, scan_scroll, KEYEVENTF_EXTENDEDKEY, 0);
+        keybd_event(vkey_scroll, scan_scroll, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
+}
+
+static bool get_scroll()
+{
+        return GetKeyState(vkey_scroll) & 1;
+}
+
+
+int main(void)
+{
+        {
+                MSG msg;
+                if(PostThreadMessage(GetCurrentThreadId(), 0, 0, 0))
+                        GetMessage(&msg, 0, 0, 0);
+        }
+        
+        while(1)
+        {
+                bool en_us = LOWORD(GetKeyboardLayout(GetWindowThreadProcessId(GetForegroundWindow(), NULL))) == 0x0409;
+                if(en_us == get_scroll()) // en_us - scroll off, else on
+                {
+                        press_scroll();
+                }
+                Sleep(200);
+        }
+        return 0;
+}
+
+
+

kbled2.c

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+#include <windows.h>
+#include <stdbool.h>
+
+static const int vkey_scroll = 0x91, // scroll lock virtual key
+        scan_scroll = 0x46, // scroll lock scancode
+        en_us_layout = 0x0409; // en_US layout (from MSDN)
+
+static void press_scroll()
+{
+        keybd_event(vkey_scroll, scan_scroll, KEYEVENTF_EXTENDEDKEY, 0);
+        keybd_event(vkey_scroll, scan_scroll, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
+}
+
+static bool get_scroll()
+{
+        return GetKeyState(vkey_scroll) & 1;
+}
+
+
+int main(void)
+{
+        {
+                // stop loading animation
+                MSG msg;
+                if(PostThreadMessage(GetCurrentThreadId(), 0, 0, 0))
+                        GetMessage(&msg, 0, 0, 0);
+        }
+
+        HKL prev_hkl;
+        DWORD prev_thread; // thread id
+        bool prev_en_us = true;
+        while(1)
+        {
+                Sleep(100);
+
+                HWND cur_window = GetForegroundWindow();
+                if(cur_window == NULL) // switching windows
+                        continue;
+                DWORD cur_thread = GetWindowThreadProcessId(cur_window, NULL);
+                HKL cur_hkl = GetKeyboardLayout(cur_thread);
+                bool en_us = LOWORD(cur_hkl) == en_us_layout;
+
+#if 0 // method 1
+                if(prev_en_us != en_us && cur_thread != prev_thread) // switched to other process with different layout
+                {
+                        // change fg window layout
+                        //ActivateKeyboardLayout(prev_hkl, KLF_ACTIVATE | KLF_SETFORPROCESS); - doesn't work (changes for our process probably)
+                        
+                        PostMessage(cur_window,
+                                    WM_INPUTLANGCHANGEREQUEST,
+                                    0,
+                                    (LPARAM)prev_hkl);
+                        en_us = prev_en_us;
+                        cur_hkl = prev_hkl;
+                }
+#else // method 2
+                if(prev_en_us != en_us && cur_thread == prev_thread) // switched layout manually
+                {
+                        // send all windows message to switch their layout
+                        // (by default windows sends it only to the current window (?))
+                        PostMessage(HWND_BROADCAST,
+                                    WM_INPUTLANGCHANGEREQUEST,
+                                    0,
+                                    (LPARAM)cur_hkl);
+                }
+#endif
+
+                static bool tried_pressing_scroll = false;
+                if(prev_en_us != en_us || prev_thread != cur_thread)
+                        tried_pressing_scroll = false;
+                // setup light
+                if(!tried_pressing_scroll && en_us == get_scroll()) // en_us - scroll off, else on
+                {
+                        press_scroll();
+                        tried_pressing_scroll = true; // dont spam scroll presses if fg program doesnt handle it correctly (emacs...)
+                }
+
+ 
+                prev_en_us = en_us;
+                prev_thread = cur_thread;
+                prev_hkl = cur_hkl;
+                
+        }
+        return 0;
+}
+
+

readme.txt

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+kbled is a small program for Windows to indicate current keyboard layout using scroll lock light on keyboard.
+kbled2 also makes keyboard layout system-wide (in Windows prior to Windows 8(?) keyboard layout is local for each application).
+
+Installation:
+1. Compile with C99 or C++ compiler
+2. Put the binary in Startup folder
+
+Known bugs:
+* currently doesn't work with default Windows terminal