devdraw/x11: fix modifier key handling for some XkbOptions

Certain XkbOptions in X11 would change keysyms for modifier keys
between the key press and key release.

For example, under the XkbOptions "grp:shifts_toggle", though shift
keys remain Shift_L/R when pressed, they become ISO_Group_Next/Prev
when released.

This behavior makes devdraw unable to detect the release event
correctly and as a result mouse button 1 click always interpreted
as button 3 event after a shift key is used.

1 files changed, 31 insertions, 12 deletions

diff --git a/src/cmd/devdraw/x11-screen.c b/src/cmd/devdraw/x11-screen.c
index 0bbc25d6..9490ab8f 100644
--- a/src/cmd/devdraw/x11-screen.c
+++ b/src/cmd/devdraw/x11-screen.c
@@ -312,6 +312,8 @@ xloop(void)
 	}
 }
 
+static int kcodecontrol, kcodealt, kcodeshift;
+
 /*
  * Handle an incoming X event.
  */
@@ -319,12 +321,15 @@ static void
 runxevent(XEvent *xev)
 {
 	int c;
+	int modp;
 	KeySym k;
 	static Mouse m;
 	XButtonEvent *be;
 	XKeyEvent *ke;
 	Xwin *w;
 
+	modp = 0;
+
 #ifdef SHOWEVENT
 	static int first = 1;
 	if(first){
@@ -424,20 +429,34 @@ runxevent(XEvent *xev)
 			break;
 		}
 
-		switch(k) {
-		case XK_Control_L:
-			if(xev->type == KeyPress)
+		if(xev->type == KeyPress)
+			switch(k) {
+			case XK_Control_L:
+			case XK_Control_R:
+				kcodecontrol = ke->keycode;
 				c |= ControlMask;
-			else
-				c &= ~ControlMask;
-			goto kbutton;
-		case XK_Alt_L:
-		case XK_Shift_L:
-			if(xev->type == KeyPress)
+				modp = 1;
+				break;
+			case XK_Alt_L:
+			case XK_Alt_R:
+				kcodealt = ke->keycode;
+				// fall through
+			case XK_Shift_L:
+			case XK_Shift_R:
+				kcodeshift = ke->keycode;
 				c |= Mod1Mask;
-			else
+				modp = 1;
+			}
+		else {
+			if(ke->keycode == kcodecontrol){
+				c &= ~ControlMask;
+				modp = 1;
+		        } else if(ke->keycode == kcodealt || ke->keycode == kcodeshift){
 				c &= ~Mod1Mask;
-		kbutton:
+				modp = 1;
+			}
+		}
+		if(modp){
 			_x.kstate = c;
 			if(m.buttons || _x.kbuttons) {
 				_x.altdown = 0; // used alt
@@ -447,8 +466,8 @@ runxevent(XEvent *xev)
 				if(c & Mod1Mask)
 					_x.kbuttons |= 4;
 				gfx_mousetrack(w->client, m.xy.x, m.xy.y, m.buttons|_x.kbuttons, m.msec);
-				break;
 			}
+			modp = 0;
 		}
 
 		if(xev->type != KeyPress)