Window flickering problem in XWin multiwindow mode

[S.J. Luo]

Hi,

I have some EDA tools running on a Linux machine and display on my Windows
PC using xorg-server-21.1.3 XWin multiwindow mode
Sometimes the application window flickers forever for an unknown reason.
The problem became more severe after my PC upgrade to Windows10.

Googling the problem, I did not find such issue reported.
I decided to take advantage of open source nature and solve it by myself.
After re-compiling and debugging, I found a calling loop triggered.
Here I eliminate the detail of the cause. I may write later if someone requires.

Knowing the root cause, I am now able to demonstrate the issue with a small
test case as well as a patch that works for me. Both are attached below.

SL

The test case:
==============
/* Compile : gcc -o flicker2 flicker2.c -lX11 */
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void SetMax(Display *dpy, Window win, int val)
{
    XEvent xev;
    Atom wm_state  =  XInternAtom(dpy, "_NET_WM_STATE", False);
    Atom max_horz  =  XInternAtom(dpy, "_NET_WM_STATE_MAXIMIZED_HORZ", False);
    Atom max_vert  =  XInternAtom(dpy, "_NET_WM_STATE_MAXIMIZED_VERT", False);

    memset(&xev, 0, sizeof(xev));
    xev.type = ClientMessage;
    xev.xclient.window = win;
    xev.xclient.message_type = wm_state;
    xev.xclient.format = 32;
    xev.xclient.data.l[0] = val; // _NET_WM_STATE_ADD or _NET_WM_STATE_REMOVE
    xev.xclient.data.l[1] = max_horz;
    xev.xclient.data.l[2] = max_vert;

    XSendEvent(dpy, DefaultRootWindow(dpy), False,
SubstructureNotifyMask, &xev);
}

int main(void) {
  Display *display;
  Window win;
  XEvent X;
  int screen;

  if (!(display = XOpenDisplay(NULL)))
    exit(1);

  screen = DefaultScreen(display);
  win = XCreateSimpleWindow(display, RootWindow(display, screen), 10,
10, 100, 100, 0,
                          BlackPixel(display, screen),
WhitePixel(display, screen));
  XMapWindow(display, win);
  SetMax(display, win, 1);
  SetMax(display, win, 0);
  XSelectInput(display, win, KeyPressMask | StructureNotifyMask);

  while (1) {
    XNextEvent(display, &X);
  }
  XCloseDisplay(display);
  return 0;
}
==============


and the patch I have applied
=======================
--- a/hw/xwin/winmultiwindowwm.c
+++ b/hw/xwin/winmultiwindowwm.c
@@ -153,6 +153,9 @@ static void

 static WMMsgNodePtr PopMessage(WMMsgQueuePtr pQueue, WMInfoPtr pWMInfo);

+static Bool
+ HaveMessage(WMMsgQueuePtr pQueue, UINT msg, xcb_window_t iWindow);
+
 static Bool
  InitQueue(WMMsgQueuePtr pQueue);

@@ -319,7 +322,6 @@ PopMessage(WMMsgQueuePtr pQueue, WMInfoPtr pWMInfo)
     return pNode;
 }

-#if 0
 /*
  * HaveMessage -
  */
@@ -331,12 +333,11 @@ HaveMessage(WMMsgQueuePtr pQueue, UINT msg,
xcb_window_t iWindow)

     for (pNode = pQueue->pHead; pNode != NULL; pNode = pNode->pNext) {
         if (pNode->msg.msg == msg && pNode->msg.iWindow == iWindow)
-            return True;
+            return TRUE;
     }

-    return False;
+    return FALSE;
 }
-#endif

 /*
  * InitQueue - Initialize the Window Manager message queue
@@ -1173,7 +1174,9 @@ winMultiWindowWMProc(void *pArg)
             break;

         case WM_WM_CHANGE_STATE:
-            UpdateState(pWMInfo, pNode->msg.iWindow, pNode->msg.dwID);
+            if(!HaveMessage(&pWMInfo->wmMsgQueue, pNode->msg.msg,
pNode->msg.iWindow))
+                UpdateState(pWMInfo, pNode->msg.iWindow, pNode->msg.dwID);
+
             break;

         default:
=======================

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