xwayland: add -noTouchPointerEmulation

In some scenarios, the Wayland compositor might have more knowledge
than the X11 server and may be able to perform pointer emulation for
touch events better. Add a command-line switch to allow compositors
to turn Xwayland pointer emulation off.

Signed-off-by: Simon Ser <contact@emersion.fr>

dix/touch.c

@@ -42,6 +42,8 @@
 
 #define TOUCH_HISTORY_SIZE 100
 
+Bool touchEmulatePointer = TRUE;
+
 /**
  * Some documentation about touch points:
  * The driver submits touch events with its own (unique) touch point ID.
@@ -142,7 +144,7 @@ TouchBeginDDXTouch(DeviceIntPtr dev, uint32_t ddx_id)
     if (!t)
         return NULL;
 
-    emulate_pointer = (t->mode == XIDirectTouch);
+    emulate_pointer = touchEmulatePointer && (t->mode == XIDirectTouch);
 
     /* Look for another active touchpoint with the same DDX ID. DDX
      * touchpoints must be unique. */

hw/xwayland/man/Xwayland.man

@@ -66,6 +66,11 @@ deprecated, use \fI\-listenfd\fP instead.
 Add given fd as a listen socket. This option is used by the \fIWayland\fP
 server to pass \fIXwayland\fP the socket where X clients connect.
 .TP 8
+.B \-noTouchPointerEmulation
+Disable touch pointer emulation. This allows the Wayland compositor to
+implement its own pointer emulation mechanism for X11 clients that don't
+support touch input.
+.TP 8
 .B \-rootless
 Run \fIXwayland\fP rootless, so that X clients integrate seamlessly with
 Wayland clients in a Wayland desktop. That requires the Wayland server

hw/xwayland/xwayland.c

@@ -95,6 +95,7 @@ ddxUseMsg(void)
     ErrorF("-shm                   use shared memory for passing buffers\n");
     ErrorF("-verbose [n]           verbose startup messages\n");
     ErrorF("-version               show the server version and exit\n");
+    ErrorF("-noTouchPointerEmulation  disable touch pointer emulation\n");
 }
 
 static int init_fd = -1;
@@ -185,6 +186,9 @@ ddxProcessArgument(int argc, char *argv[], int i)
         xwl_show_version();
         exit(0);
     }
+    else if (strcmp(argv[i], "-noTouchPointerEmulation") == 0) {
+        touchEmulatePointer = FALSE;
+    }
 
     return 0;
 }

hw/xwayland/xwayland.pc.in

@@ -11,3 +11,4 @@ have_initfd=true
 have_listenfd=true
 have_verbose=true
 have_terminate_delay=true
+have_no_touch_pointer_emulation=true

include/dix.h

@@ -147,6 +147,7 @@ extern _X_EXPORT ClientPtr serverClient;
 extern _X_EXPORT int currentMaxClients;
 extern _X_EXPORT char dispatchExceptionAtReset;
 extern _X_EXPORT int terminateDelay;
+extern _X_EXPORT Bool touchEmulatePointer;
 
 typedef int HWEventQueueType;
 typedef HWEventQueueType *HWEventQueuePtr;