keycode.c

/* http://stackoverflow.com/questions/1918841/how-to-convert-ascii-character-to-cgkeycode */

#include <Carbon/Carbon.h> /* For kVK_ constants, and TIS functions. */
#include "keycode.h"

/* Returns string representation of key, if it is printable.
 * Ownership follows the Create Rule; that is, it is the caller's
 * responsibility to release the returned object. */
CFStringRef createStringForKey(CGKeyCode keyCode)
{
    TISInputSourceRef currentKeyboard = TISCopyCurrentKeyboardInputSource();
    CFDataRef layoutData =
        TISGetInputSourceProperty(currentKeyboard,
                                  kTISPropertyUnicodeKeyLayoutData);
    const UCKeyboardLayout *keyboardLayout =
        (const UCKeyboardLayout *)CFDataGetBytePtr(layoutData);

    UInt32 keysDown = 0;
    UniChar chars[4];
    UniCharCount realLength;

    UCKeyTranslate(keyboardLayout,
                   keyCode,
                   kUCKeyActionDisplay,
                   0,
                   LMGetKbdType(),
                   kUCKeyTranslateNoDeadKeysBit,
                   &keysDown,
                   sizeof(chars) / sizeof(chars[0]),
                   &realLength,
                   chars);
    CFRelease(currentKeyboard);    

    return CFStringCreateWithCharacters(kCFAllocatorDefault, chars, 1);
}

/* Returns key code for given character via the above function, or UINT16_MAX
 * on error. */
CGKeyCode keyCodeForChar(const char c)
{
    static CFMutableDictionaryRef charToCodeDict = NULL;
    CGKeyCode code;
    UniChar character = c;
    CFStringRef charStr = NULL;

    /* Generate table of keycodes and characters. */
    if (charToCodeDict == NULL) {
        size_t i;
        charToCodeDict = CFDictionaryCreateMutable(kCFAllocatorDefault,
                                                   128,
                                                   &kCFCopyStringDictionaryKeyCallBacks,
                                                   NULL);
        if (charToCodeDict == NULL) return UINT16_MAX;

        /* Loop through every keycode (0 - 127) to find its current mapping. */
        for (i = 0; i < 128; ++i) {
            CFStringRef string = createStringForKey((CGKeyCode)i);
            if (string != NULL) {
                CFDictionaryAddValue(charToCodeDict, string, (const void *)i);
                CFRelease(string);
            }
        }
    }

    charStr = CFStringCreateWithCharacters(kCFAllocatorDefault, &character, 1);

    /* Our values may be NULL (0), so we need to use this function. */
    if (!CFDictionaryGetValueIfPresent(charToCodeDict, charStr,
                                       (const void **)&code)) {
        code = UINT16_MAX;
    }

    CFRelease(charStr);
    return code;
}