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More cleverness in midend_process_key()

It now strips off modifier flags from keys that shouldn't have them and
maps printable characters with MOD_CTRL to the corresponding control
characters.  It also catches Ctrl+Shift+Z because that obviously belongs
in the midend.

I've updated the JavaScript front-end to take advantage of these
changes.  Other front ends are unchanged and should work just as they
did before.

--- a/devel.but

+++ b/devel.but

@@ -3191,8 +3191,9 @@

 The parameters \c{x} and \c{y} are identical to the ones passed to the

 back end function \cw{interpret_move()} (\k{backend-interpret-move}).

-\c{button} is \e{almost} identical to the parameter passed to

-\cw{interpret_move()}. However, some additional special button values

+\c{button} is similar to the parameter passed to

+\cw{interpret_move()}. However, the midend is more relaxed about

+values passed to in, and some additional special button values

 are defined for the front end to pass to the midend (see below).

 Also, the front end is \e{not} required to provide guarantees about

@@ -3265,6 +3266,11 @@

 items the same, by translating each of them into a button code passed

 to the midend, and handle quitting by noticing the \c{false} return

 value from \cw{midend_process_key()}.)

+

+The midend tolerates any modifier being set on any key and removes

+them as necessary before passing the key on to the backend.  It will

+also handle translating printable characters combined with

+\cw{MOD_CTRL} into control characters.

 \H{midend-request-keys} \cw{midend_request_keys()}

--- a/emcc.c

+++ b/emcc.c

@@ -408,19 +408,9 @@

         keyevent = keycode;

     if (keyevent >= 0) {

-        if (shift && (keyevent >= 0x100 && !IS_UI_FAKE_KEY(keyevent)))

-            keyevent |= MOD_SHFT;

-

-        if (ctrl && !IS_UI_FAKE_KEY(keyevent)) {

-            if (keyevent >= 0x100)

-                keyevent |= MOD_CTRL;

-            else

-                keyevent &= 0x1F;

-        }

-

-        if ('0' <= keyevent && keyevent <= '9' &&

-            location == DOM_KEY_LOCATION_NUMPAD)

-            keyevent |= MOD_NUM_KEYPAD;

+        if (shift) keyevent |= MOD_SHFT;

+        if (ctrl) keyevent |= MOD_CTRL;

+        if (location == DOM_KEY_LOCATION_NUMPAD) keyevent |= MOD_NUM_KEYPAD;

         midend_process_key(me, 0, 0, keyevent, &handled);

         post_move();

--- a/midend.c

+++ b/midend.c

@@ -1140,6 +1140,10 @@

      * of '\n' etc for keyboard-based cursors. The choice of buttons

      * here could eventually be controlled by a runtime configuration

      * option.

+     *

+     * We also handle converting MOD_CTRL|'a' etc into '\x01' etc,

+     * specially recognising Ctrl+Shift+Z, and stripping modifier

+     * flags off keys that aren't meant to have them.

      */

     if (IS_MOUSE_DRAG(button) || IS_MOUSE_RELEASE(button)) {

         if (me->pressed_mouse_button) {

@@ -1169,6 +1173,18 @@

                         (LEFT_RELEASE - LEFT_BUTTON)), handled);

     }

+    /* Canonicalise CTRL+ASCII. */

+    if ((button & MOD_CTRL) && (button & ~MOD_MASK) < 0x80)

+        button = button & (0x1f | (MOD_MASK & ~MOD_CTRL));

+    /* Special handling to make CTRL+SHFT+Z into REDO. */

+    if ((button & (~MOD_MASK | MOD_SHFT)) == (MOD_SHFT | '\x1A'))

+        button = UI_REDO;

+    /* interpret_move() expects CTRL and SHFT only on cursor keys. */

+    if (!IS_CURSOR_MOVE(button & ~MOD_MASK))

+        button &= ~(MOD_CTRL | MOD_SHFT);

+    /* ... and NUM_KEYPAD only on ASCII values. */

+    if ((button & ~MOD_MASK) >= 0x80)

+        button &= ~MOD_NUM_KEYPAD;

     /*

      * Translate keyboard presses to cursor selection.

      */