[hackers] [PATCH 1/5] allow neutralizing a key modifier by applying the same modifier again

[Maarten van Gompel]

From: Max Schillinger <maxschillin...@web.de>

svkbd allows you to create keys for symbols of the second (=shift) layer by 
defining them with a modifier included, like:

    { "|", "|", XK_backslash, 1, XK_Shift_L },

This key creates a pipe symbol by sending shift + backslash. But unfortunately, 
this way you can't emit get the original symbol (backslash) anymore. So you 
still need a separate key for typing a backslash, wasting precious space on the 
screen.

The appended patch fixes this by allowing to neutralize the shift by tapping 
this key with shift. It works both by tapping first shift, then the pipe key on 
the on-screen keyboard, or by clicking the pipe key with the middle mouse 
button (assuming XK_Shift_L is set as the button 2 mod).

This way you can create a "flipped" backslash/pipe key:

    { "|", "\\", XK_backslash, 1, XK_Shift_L },

This patch works equally for AltGr symbols in a `de`-based layout. For example:

    { "~", "+", XK_plus, 1, XK_ISO_Level3_Shift },

(In the German QWERTZ layout, you enter "~" with AltGr-"+".)

Best regards,
Max

Signed-off-by: Maarten van Gompel <proy...@anaproy.nl>
---
 svkbd.c | 36 +++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/svkbd.c b/svkbd.c
index f9b951d..61778c6 100644
--- a/svkbd.c
+++ b/svkbd.c
@@ -198,16 +198,19 @@ buttonpress(XEvent *e)
        if (!(k = findkey(ev->x, ev->y)))
                return;
 
-       if (k->modifier) {
-               mod = k->modifier;
-       } else {
-               for (i = 0; i < LENGTH(buttonmods); i++) {
-                       if (ev->button == buttonmods[i].button) {
-                               mod = buttonmods[i].mod;
-                               break;
-                       }
+       for (i = 0; i < LENGTH(buttonmods); i++) {
+               if (ev->button == buttonmods[i].button) {
+                       mod = buttonmods[i].mod;
+                       break;
                }
        }
+
+       if (k->modifier) {
+               if (mod == k->modifier)
+                       mod = 0;
+               else
+                       mod = k->modifier;
+       }
        press(k, mod);
 }
 
@@ -231,7 +234,9 @@ buttonrelease(XEvent *e)
        if (ev->x < 0 || ev->y < 0) {
                unpress(NULL, mod);
        } else if ((k = findkey(ev->x, ev->y))) {
-               if (k->modifier)
+               if (k->modifier == mod)
+                       unpress(k, 0);
+               else if (k->modifier)
                        unpress(k, k->modifier);
                else
                        unpress(k, mod);
@@ -564,6 +569,7 @@ void
 unpress(Key *k, KeySym buttonmod)
 {
        int i;
+       Bool neutralizebuttonmod = False;
 
        if (k != NULL) {
                switch(k->keysym) {
@@ -589,10 +595,13 @@ unpress(Key *k, KeySym buttonmod)
                /* simulate the press event, as we postponed it earlier in 
press() */
                for (i = 0; i < numkeys; i++) {
                        if (keys[i].pressed && IsModifierKey(keys[i].keysym)) {
-                               simulate_keypress(keys[i].keysym);
+                               if (keys[i].keysym == buttonmod)
+                                       neutralizebuttonmod = True;
+                               else
+                                       simulate_keypress(keys[i].keysym);
                        }
                }
-               if (buttonmod) {
+               if (buttonmod && !neutralizebuttonmod) {
                        simulate_keypress(buttonmod);
                }
                simulate_keypress(k->keysym);
@@ -615,14 +624,15 @@ unpress(Key *k, KeySym buttonmod)
                }
        }
 
-       if (buttonmod) {
+       if (buttonmod && !neutralizebuttonmod) {
                simulate_keyrelease(buttonmod);
        }
 
        if ((k == NULL) || (!IsModifierKey(k->keysym))) {
                for (i = 0; i < numkeys; i++) {
                        if (keys[i].pressed && IsModifierKey(keys[i].keysym)) {
-                               simulate_keyrelease(keys[i].keysym);
+                               if (!(keys[i].keysym == buttonmod && 
neutralizebuttonmod))
+                                       simulate_keyrelease(keys[i].keysym);
                                keys[i].pressed = 0;
                                drawkey(&keys[i]);
                        }
-- 
2.32.0