emscripten: Make an attempt at correct keyboard scancode/keycodes.

This uses a newer browser API to get physical scancodes, but still
uses the (deprecated) event field that we were already using for
scancodes, but for keycodes instead now, which appears to be more
accurate.

Since keyboard layout isn't (generally) available to web apps, this
adds an internal interface to send key events with both scancode
and keycode to SDL's internals, instead of sending just scancodes and
expecting SDL to use its own keymap to generate keycodes.

Future work in this area would be to use the keyboard layout APIs
on browsers that support them, which would allow us to use SDL's
usual keymap code and not rely on a deprecated browser API, but
until we get there, this patch gives significantly more correct
results than we would have before.

Fixes #2098.

Author: icculus

src/events/SDL_keyboard.c

@@ -800,12 +800,11 @@ SDL_SetKeyboardFocus(SDL_Window * window)
 }
 
 static int
-SDL_SendKeyboardKeyInternal(Uint8 source, Uint8 state, SDL_Scancode scancode)
+SDL_SendKeyboardKeyInternal(Uint8 source, Uint8 state, SDL_Scancode scancode, SDL_Keycode keycode)
 {
     SDL_Keyboard *keyboard = &SDL_keyboard;
     int posted;
     SDL_Keymod modifier;
-    SDL_Keycode keycode;
     Uint32 type;
     Uint8 repeat = SDL_FALSE;
 
@@ -851,7 +850,9 @@ SDL_SendKeyboardKeyInternal(Uint8 source, Uint8 state, SDL_Scancode scancode)
     /* Update internal keyboard state */
     keyboard->keystate[scancode] = state;
 
-    keycode = keyboard->keymap[scancode];
+    if (keycode == SDLK_UNKNOWN) {
+        keycode = keyboard->keymap[scancode];
+    }
 
     if (source == KEYBOARD_AUTORELEASE) {
         keyboard->autorelease_pending = SDL_TRUE;
@@ -971,13 +972,19 @@ SDL_SendKeyboardUnicodeKey(Uint32 ch)
 int
 SDL_SendKeyboardKey(Uint8 state, SDL_Scancode scancode)
 {
-    return SDL_SendKeyboardKeyInternal(KEYBOARD_HARDWARE, state, scancode);
+    return SDL_SendKeyboardKeyInternal(KEYBOARD_HARDWARE, state, scancode, SDLK_UNKNOWN);
+}
+
+int
+SDL_SendKeyboardKeyComplete(Uint8 state, SDL_Scancode scancode, SDL_Keycode keycode)
+{
+    return SDL_SendKeyboardKeyInternal(KEYBOARD_HARDWARE, state, scancode, keycode);
 }
 
 int
 SDL_SendKeyboardKeyAutoRelease(SDL_Scancode scancode)
 {
-    return SDL_SendKeyboardKeyInternal(KEYBOARD_AUTORELEASE, SDL_PRESSED, scancode);
+    return SDL_SendKeyboardKeyInternal(KEYBOARD_AUTORELEASE, SDL_PRESSED, scancode, SDLK_UNKNOWN);
 }
 
 void
@@ -989,7 +996,7 @@ SDL_ReleaseAutoReleaseKeys(void)
     if (keyboard->autorelease_pending) {
         for (scancode = SDL_SCANCODE_UNKNOWN; scancode < SDL_NUM_SCANCODES; ++scancode) {
             if (keyboard->keysource[scancode] == KEYBOARD_AUTORELEASE) {
-                SDL_SendKeyboardKeyInternal(KEYBOARD_AUTORELEASE, SDL_RELEASED, scancode);
+                SDL_SendKeyboardKeyInternal(KEYBOARD_AUTORELEASE, SDL_RELEASED, scancode, SDLK_UNKNOWN);
             }
         }
         keyboard->autorelease_pending = SDL_FALSE;

src/events/SDL_keyboard_c.h

@@ -53,6 +53,10 @@ extern int SDL_SendKeyboardUnicodeKey(Uint32 ch);
 extern int SDL_SendKeyboardKey(Uint8 state, SDL_Scancode scancode);
 extern int SDL_SendKeyboardKeyAutoRelease(SDL_Scancode scancode);
 
+/* This is for platforms that don't know the keymap but can report scancode and keycode directly.
+   Most platforms should prefer to optionally call SDL_SetKeymap and then use SDL_SendKeyboardKey. */
+extern int SDL_SendKeyboardKeyComplete(Uint8 state, SDL_Scancode scancode, SDL_Keycode keycode);
+
 /* Release all the autorelease keys */
 extern void SDL_ReleaseAutoReleaseKeys(void);