
/* Copyright (c) Mark J. Kilgard, 1994. */

/* This program is freely distributable without licensing fees
   and is provided without guarantee or warrantee expressed or
   implied. This program is -not- in the public domain. */

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <assert.h>

#include <X11/Xlib.h>
#include <X11/cursorfont.h>  /* for XC_arrow */

#include <GL/glut.h>
#include "glutint.h"
#include "layerutil.h"

GLUTmenu *__glutCurrentMenu = NULL;
void (*__glutMenuStatusFunc) (int, int, int);
GLUTmenu *__glutMappedMenu;
GLUTwindow *__glutMenuWindow;
GLUTmenuItem *__glutItemSelected;

static GLUTmenu **menuList = NULL;
static int menuListSize = 0;
static XFontStruct *menuFont = NULL;
static Cursor menuCursor;
static Colormap menuColormap;
static Visual *menuVisual;
static int menuDepth;
static int fontHeight;
static GC blackGC, grayGC, whiteGC;
static unsigned long menuBlack, menuWhite, menuGray;
static unsigned long useSaveUnders;

/* A replacement for XAllocColor (originally by Brian Paul).
   This  function should never fail to allocate a color.  When
   XAllocColor fails, we return the nearest matching color.  If
   we have to allocate many colors this function isn't a great
   solution; the XQueryColors() could be done just once.  */
static void
noFaultXAllocColor(Display * dpy, Colormap cmap, int cmapSize,
  XColor * color)
{
  XColor *ctable, subColor;
  int i, bestmatch;
  double mindist;       /* 3*2^16^2 exceeds long int precision. 
                         */

  for (;;) {
    /* First try just using XAllocColor. */
    if (XAllocColor(dpy, cmap, color))
      return;

    /* Retrieve color table entries. */
    /* XXX alloca candidate. */
    ctable = (XColor *) malloc(cmapSize * sizeof(XColor));
    for (i = 0; i < cmapSize; i++)
      ctable[i].pixel = i;
    XQueryColors(dpy, cmap, ctable, cmapSize);

    /* Find best match. */
    bestmatch = -1;
    mindist = 0.0;
    for (i = 0; i < cmapSize; i++) {
      double dr = (double) color->red - (double) ctable[i].red;
      double dg = (double) color->green - (double) ctable[i].green;
      double db = (double) color->blue - (double) ctable[i].blue;
      double dist = dr * dr + dg * dg + db * db;
      if (bestmatch < 0 || dist < mindist) {
        bestmatch = i;
        mindist = dist;
      }
    }

    /* Return result. */
    subColor.red = ctable[bestmatch].red;
    subColor.green = ctable[bestmatch].green;
    subColor.blue = ctable[bestmatch].blue;
    free(ctable);
    if (XAllocColor(dpy, cmap, &subColor)) {
      *color = subColor;
      return;
    }
    /* Extremely unlikely, but possibly color was deallocated
       and reallocated by someone else before we could
       XAllocColor the color cell we located.  If so, loop
       again... */
  }
}

static void
menuVisualSetup(void)
{
  XLayerVisualInfo template, *visual, *overlayVisuals;
  XColor color;
  Status status;
  Bool presumablyMesa;
  int layer, nVisuals, i, dummy;

  for (layer = 3; layer > 0; layer--) {
    template.layer = layer;
    template.vinfo.screen = __glutScreen;
    overlayVisuals = __glutXGetLayerVisualInfo(__glutDisplay,
      VisualScreenMask | VisualLayerMask, &template, &nVisuals);
    if (overlayVisuals) {
      for (i = 0; i < nVisuals; i++) {
        visual = &overlayVisuals[i];
        if (visual->vinfo.colormap_size >= 3) {
          menuColormap = XCreateColormap(__glutDisplay, __glutRoot,
            visual->vinfo.visual, AllocNone);
          /* Allocate overlay colormap cells in defined order:
             gray, black, white to match the IRIS GL allocation
             scheme.  Increases likelihood of less overlay
             colormap flashing. */
          /* XXX nice if these 3 AllocColor's could be done in
             one protocol round-trip */
          color.red = color.green = color.blue = 0xaa00;
          status = XAllocColor(__glutDisplay,
            menuColormap, &color);
          if (!status) {
            XFreeColormap(__glutDisplay, menuColormap);
            continue;
          }
          menuGray = color.pixel;
          color.red = color.green = color.blue = 0x0000;
          status = XAllocColor(__glutDisplay,
            menuColormap, &color);
          if (!status) {
            XFreeColormap(__glutDisplay, menuColormap);
            continue;
          }
          menuBlack = color.pixel;
          color.red = color.green = color.blue = 0xffff;
          status = XAllocColor(__glutDisplay,
            menuColormap, &color);
          if (!status) {
            XFreeColormap(__glutDisplay, menuColormap);
            continue;
          }
          menuWhite = color.pixel;
          menuVisual = visual->vinfo.visual;
          menuDepth = visual->vinfo.depth;
          /* If using overlays, avoid requesting "save unders". 
           */
          useSaveUnders = 0;
          XFree(overlayVisuals);
          return;
        }
      }
      XFree(overlayVisuals);
    }
  }
  /* settle for default visual */
  menuVisual = DefaultVisual(__glutDisplay, __glutScreen);
  menuDepth = DefaultDepth(__glutDisplay, __glutScreen);
  menuColormap = DefaultColormap(__glutDisplay, __glutScreen);
  menuBlack = BlackPixel(__glutDisplay, __glutScreen);
  menuWhite = WhitePixel(__glutDisplay, __glutScreen);
  color.red = color.green = color.blue = 0xaa00;
  noFaultXAllocColor(__glutDisplay, menuColormap,
    menuVisual->map_entries, &color);
  menuGray = color.pixel;

  /* When no overlays are supported, we would like to use X
     "save unders" to avoid exposes to windows obscured by
     pop-up menus.  However, OpenGL's direct rendering support
     means OpenGL interacts poorly with X backing store and
     save unders.  X servers do not (in implementation
     practice) redirect OpenGL rendering destined to obscured
     window regions into backing store.

     Implementation solutions exist for this problem, but they
     are expensive and high-end OpenGL implementations
     typically provide fast rendering and/or overlays to
     obviate the problem associated of user interfaces (pop-up
     menus) forcing redraws of complex normal plane scenes.
     (See support for overlays pop-up menus above.)

     Mesa 3D, however, does not support direct rendering.
     Overlays are often unavailable to Mesa, and Mesa is also
     relatively slow.  For these reasons, Mesa-rendering GLUT
     programs can and should use X save unders.

     Look for the GLX extension.  If _not_ supported, we are
     presumably using Mesa so enable save unders. */

  presumablyMesa = !XQueryExtension(__glutDisplay, "GLX",
    &dummy, &dummy, &dummy);

  if (presumablyMesa)
    useSaveUnders = CWSaveUnder;
  else
    useSaveUnders = 0;
}

static void
menuSetup(void)
{
  if (menuFont) {
    /* menuFont overload to indicate menu initialization */
    return;
  }
  menuFont = XLoadQueryFont(__glutDisplay,
    "-*-helvetica-bold-o-normal--14-*-*-*-p-*-iso8859-1");
  if (!menuFont) {
    /* try back up font */
    menuFont = XLoadQueryFont(__glutDisplay, "fixed");
  }
  if (!menuFont) {
    __glutFatalError("could not load font.");
  }
  menuVisualSetup();
  fontHeight = menuFont->ascent + menuFont->descent;
  menuCursor = XCreateFontCursor(__glutDisplay, XC_arrow);
}

static void
menuGraphicsContextSetup(Window win)
{
  XGCValues gcvals;

  if (blackGC != None)
    return;
  gcvals.font = menuFont->fid;
  gcvals.foreground = menuBlack;
  blackGC = XCreateGC(__glutDisplay, win,
    GCFont | GCForeground, &gcvals);
  gcvals.foreground = menuGray;
  grayGC = XCreateGC(__glutDisplay, win, GCForeground, &gcvals);
  gcvals.foreground = menuWhite;
  whiteGC = XCreateGC(__glutDisplay, win, GCForeground, &gcvals);
}

/* OBSOLETE - use glutMenuStatusFunc instead. */
void
glutMenuStateFunc(GLUTmenuStateCB menuStateFunc)
{
  __glutMenuStatusFunc = (GLUTmenuStatusCB) menuStateFunc;
}

void
glutMenuStatusFunc(GLUTmenuStatusCB menuStatusFunc)
{
  __glutMenuStatusFunc = menuStatusFunc;
}

void
__glutSetMenu(GLUTmenu * menu)
{
  __glutCurrentMenu = menu;
}

static void
unmapMenu(GLUTmenu * menu)
{
  if (menu->cascade) {
    unmapMenu(menu->cascade);
    menu->cascade = NULL;
  }
  menu->anchor = NULL;
  menu->highlighted = NULL;
  XUnmapWindow(__glutDisplay, menu->win);
}

void
__glutFinishMenu(Window win, int x, int y)
{
  Window dummy;
  int rc;

  unmapMenu(__glutMappedMenu);
  XUngrabPointer(__glutDisplay, CurrentTime);

  /* This XFlush is needed to to make sure the pointer is
     really ungrabbed when the application's menu callback is
     called. Otherwise, a deadlock might happen because the
     application may try to read from an terminal window, but
     yet the ungrab hasn't really happened since it hasn't been
     flushed out. */
  XFlush(__glutDisplay);

  if (__glutMenuStatusFunc) {
    if (win != __glutMenuWindow->win) {
      /* The button release may have occurred in a window other
         than the window requesting the pop-up menu (for
         example, one of the submenu windows).  In this case, we
         need to translate the coordinates into the coordinate
         system of the window associated with the window. */
      rc = XTranslateCoordinates(__glutDisplay, win, __glutMenuWindow->win,
        x, y, &x, &y, &dummy);
      assert(rc != False);  /* Will always be on same screen. */
    }
    __glutSetWindow(__glutMenuWindow);
    __glutSetMenu(__glutMappedMenu);

    /* Setting __glutMappedMenu to NULL permits operations that
       change menus or destroy the menu window again. */
    __glutMappedMenu = NULL;

    __glutMenuStatusFunc(GLUT_MENU_NOT_IN_USE, x, y);
  }
  /* Setting __glutMappedMenu to NULL permits operations that
     change menus or destroy the menu window again. */
  __glutMappedMenu = NULL;

  /* If an item is selected and it is not a submenu trigger,
     generate menu callback. */
  if (__glutItemSelected && !__glutItemSelected->isTrigger) {
    __glutSetWindow(__glutMenuWindow);
    /* When menu callback is triggered, current menu should be
       set to the callback menu. */
    __glutSetMenu(__glutItemSelected->menu);
    __glutItemSelected->menu->select(
      __glutItemSelected->value);
  }
  __glutMenuWindow = NULL;
}

#define MENU_BORDER 1
#define MENU_GAP 2
#define MENU_ARROW_GAP 6
#define MENU_ARROW_WIDTH 8

static void
mapMenu(GLUTmenu * menu, int x, int y)
{
  XWindowChanges changes;
  unsigned int mask;
  int subMenuExtension, num;

  /* If there are submenus, we need to provide extra space for
     the submenu pull arrow.  */
  if (menu->submenus > 0) {
    subMenuExtension = MENU_ARROW_GAP + MENU_ARROW_WIDTH;
  } else {
    subMenuExtension = 0;
  }

  changes.stack_mode = Above;
  mask = CWStackMode | CWX | CWY;
  /* If the menu isn't managed (ie, validated so all the
     InputOnly subwindows are the right size), do so.  */
  if (!menu->managed) {
    GLUTmenuItem *item;

    item = menu->list;
    num = menu->num;
    while (item) {
      XWindowChanges itemupdate;

      itemupdate.y = (num - 1) * fontHeight + MENU_GAP;
      itemupdate.width = menu->pixwidth;
      itemupdate.width += subMenuExtension;
      XConfigureWindow(__glutDisplay, item->win,
        CWWidth | CWY, &itemupdate);
      item = item->next;
      num--;
    }
    menu->pixheight = MENU_GAP +
      fontHeight * menu->num + MENU_GAP;
    changes.height = menu->pixheight;
    changes.width = MENU_GAP +
      menu->pixwidth + subMenuExtension + MENU_GAP;
    mask |= CWWidth | CWHeight;
    menu->managed = True;
  }
  /* make sure menu appears fully on screen */
  if (y + menu->pixheight >= __glutScreenHeight) {
    changes.y = __glutScreenHeight - menu->pixheight;
  } else {
    changes.y = y;
  }
  if (x + menu->pixwidth + subMenuExtension >=
    __glutScreenWidth) {
    changes.x = __glutScreenWidth -
      menu->pixwidth + subMenuExtension;
  } else {
    changes.x = x;
  }

  /* Remember where the menu is placed so submenus can be
     properly placed relative to it. */
  menu->x = changes.x;
  menu->y = changes.y;

  XConfigureWindow(__glutDisplay, menu->win, mask, &changes);
  XInstallColormap(__glutDisplay, menuColormap);
  /* XXX The XRaiseWindow below should not be necessary because
     the XConfigureWindow requests an Above stack mode (same as
     XRaiseWindow), but some Sun users complained this was still
     necessary.  Probably some window manager or X server bug on
     these machines?? */
  XRaiseWindow(__glutDisplay, menu->win);
  XMapWindow(__glutDisplay, menu->win);
}

void
__glutStartMenu(GLUTmenu * menu, GLUTwindow * window,
  int x, int y, int x_win, int y_win)
{
  int grab;

  assert(__glutMappedMenu == NULL);
  grab = XGrabPointer(__glutDisplay, __glutRoot, True,
    ButtonPressMask | ButtonReleaseMask,
    GrabModeAsync, GrabModeAsync,
    __glutRoot, menuCursor, CurrentTime);
  if (grab != GrabSuccess) {
    /* Somebody else has pointer grabbed, ignore menu
       activation. */
    return;
  }
  __glutMappedMenu = menu;
  __glutMenuWindow = window;
  __glutItemSelected = NULL;
  if (__glutMenuStatusFunc) {
    __glutSetMenu(menu);
    __glutSetWindow(window);
    __glutMenuStatusFunc(GLUT_MENU_IN_USE, x_win, y_win);
  }
  mapMenu(menu, x, y);
}

static void
paintSubMenuArrow(Window win, int x, int y)
{
  XPoint p[5];

  p[0].x = p[4].x = x;
  p[0].y = p[4].y = y - menuFont->ascent + 1;
  p[1].x = p[0].x + MENU_ARROW_WIDTH - 1;
  p[1].y = p[0].y + (menuFont->ascent / 2) - 1;
  p[2].x = p[1].x;
  p[2].y = p[1].y + 1;
  p[3].x = p[0].x;
  p[3].y = p[0].y + menuFont->ascent - 2;
  XFillPolygon(__glutDisplay, win,
    whiteGC, p, 4, Convex, CoordModeOrigin);
  XDrawLines(__glutDisplay, win, blackGC, p, 5, CoordModeOrigin);
}

static void
paintMenuItem(GLUTmenuItem * item, int num)
{
  Window win = item->menu->win;
  GC gc;
  int y;
  int subMenuExtension;

  if (item->menu->submenus > 0) {
    subMenuExtension = MENU_ARROW_GAP + MENU_ARROW_WIDTH;
  } else {
    subMenuExtension = 0;
  }
  if (item->menu->highlighted == item) {
    gc = whiteGC;
  } else {
    gc = grayGC;
  }
  y = MENU_GAP + fontHeight * num - menuFont->descent;
  XFillRectangle(__glutDisplay, win, gc,
    MENU_GAP, y - fontHeight + menuFont->descent,
    item->menu->pixwidth + subMenuExtension, fontHeight);
  XDrawString(__glutDisplay, win, blackGC,
    MENU_GAP, y, item->label, item->len);
  if (item->isTrigger) {
    paintSubMenuArrow(win,
      item->menu->pixwidth + MENU_ARROW_GAP + 1, y);
  }
}

void
__glutPaintMenu(GLUTmenu * menu)
{
  GLUTmenuItem *item;
  int i = menu->num;
  int y = MENU_GAP + fontHeight * i - menuFont->descent;

  item = menu->list;
  while (item) {
    if (item->menu->highlighted == item) {
      paintMenuItem(item, i);
    } else {
      /* quick render of the menu item; assume background
         already cleared to gray */
      XDrawString(__glutDisplay, menu->win, blackGC,
        2, y, item->label, item->len);
      if (item->isTrigger) {
        paintSubMenuArrow(menu->win,
          menu->pixwidth + MENU_ARROW_GAP + 1, y);
      }
    }
    i--;
    y -= fontHeight;
    item = item->next;
  }
}

GLUTmenuItem *
__glutGetMenuItem(GLUTmenu * menu, Window win, int *which)
{
  GLUTmenuItem *item;
  int i;

  i = menu->num;
  item = menu->list;
  while (item) {
    if (item->win == win) {
      *which = i;
      return item;
    }
    if (item->isTrigger) {
      GLUTmenuItem *subitem;

      subitem = __glutGetMenuItem(menuList[item->value],
        win, which);
      if (subitem) {
        return subitem;
      }
    }
    i--;
    item = item->next;
  }
  return NULL;
}

static int
getMenuItemIndex(GLUTmenuItem * item)
{
  int count = 0;

  while (item) {
    count++;
    item = item->next;
  }
  return count;
}

GLUTmenu *
__glutGetMenu(Window win)
{
  GLUTmenu *menu;

  menu = __glutMappedMenu;
  while (menu) {
    if (win == menu->win) {
      return menu;
    }
    menu = menu->cascade;
  }
  return NULL;
}

GLUTmenu *
__glutGetMenuByNum(int menunum)
{
  if (menunum < 1 || menunum > menuListSize) {
    return NULL;
  }
  return menuList[menunum - 1];
}

static int
getUnusedMenuSlot(void)
{
  int i;

  /* Look for allocated, unused slot. */
  for (i = 0; i < menuListSize; i++) {
    if (!menuList[i]) {
      return i;
    }
  }
  /* Allocate a new slot. */
  menuListSize++;
  if (menuList) {
    menuList = (GLUTmenu **)
      realloc(menuList, menuListSize * sizeof(GLUTmenu *));
  } else {
    /* XXX Some realloc's do not correctly perform a malloc
       when asked to perform a realloc on a NULL pointer,
       though the ANSI C library spec requires this. */
    menuList = (GLUTmenu **) malloc(sizeof(GLUTmenu *));
  }
  if (!menuList)
    __glutFatalError("out of memory.");
  menuList[menuListSize - 1] = NULL;
  return menuListSize - 1;
}

static void
menuModificationError(void)
{
  /* XXX Remove the warning after GLUT 3.0. */
  __glutWarning("The following is a new check for GLUT 3.0; update your code.");
  __glutFatalError("menu manipulation not allowed while menus in use");
}

int
glutCreateMenu(GLUTselectCB selectFunc)
{
  XSetWindowAttributes wa;
  GLUTmenu *menu;
  int menuid;

  if (__glutMappedMenu)
    menuModificationError();
  if (!__glutDisplay)
    __glutOpenXConnection(NULL);
  menuid = getUnusedMenuSlot();
  menu = (GLUTmenu *) malloc(sizeof(GLUTmenu));
  if (!menu)
    __glutFatalError("out of memory.");
  menu->id = menuid;
  menu->num = 0;
  menu->submenus = 0;
  menu->managed = False;
  menu->pixwidth = 0;
  menu->select = selectFunc;
  menu->list = NULL;
  menu->cascade = NULL;
  menu->highlighted = NULL;
  menu->anchor = NULL;
  menuSetup();
  wa.override_redirect = True;
  wa.background_pixel = menuGray;
  wa.border_pixel = menuBlack;
  wa.colormap = menuColormap;
  wa.event_mask = StructureNotifyMask | ExposureMask |
    ButtonPressMask | ButtonReleaseMask |
    EnterWindowMask | LeaveWindowMask;
  /* Save unders really only enabled if useSaveUnders is set to
     CWSaveUnder, ie. using Mesa 3D.  See earlier comments. */
  wa.save_under = True;
  menu->win = XCreateWindow(__glutDisplay, __glutRoot,
  /* real position determined when mapped */
    0, 0,
  /* real size will be determined when menu is managed */
    1, 1,
    MENU_BORDER, menuDepth, InputOutput, menuVisual,
    CWOverrideRedirect | CWBackPixel | CWBorderPixel |
    CWEventMask | CWColormap | useSaveUnders,
    &wa);
  menuGraphicsContextSetup(menu->win);
  menuList[menuid] = menu;
  __glutSetMenu(menu);
  return menuid + 1;
}

void
glutDestroyMenu(int menunum)
{
  GLUTmenu *menu = __glutGetMenuByNum(menunum);
  GLUTmenuItem *item, *next;

  if (__glutMappedMenu)
    menuModificationError();
  assert(menu->id == menunum - 1);
  XDestroySubwindows(__glutDisplay, menu->win);
  XDestroyWindow(__glutDisplay, menu->win);
  menuList[menunum - 1] = NULL;
  /* free all menu entries */
  item = menu->list;
  while (item) {
    assert(item->menu == menu);
    next = item->next;
    free(item->label);
    free(item);
    item = next;
  }
  if (__glutCurrentMenu == menu) {
    __glutCurrentMenu = NULL;
  }
  free(menu);
}

int
glutGetMenu(void)
{
  if (__glutCurrentMenu) {
    return __glutCurrentMenu->id + 1;
  } else {
    return 0;
  }
}

void
glutSetMenu(int menuid)
{
  GLUTmenu *menu;

  if (menuid < 1 || menuid > menuListSize) {
    __glutWarning("glutSetMenu attempted on bogus menu.");
    return;
  }
  menu = menuList[menuid - 1];
  if (!menu) {
    __glutWarning("glutSetMenu attempted on bogus menu.");
    return;
  }
  __glutSetMenu(menu);
}

static void
setMenuItem(GLUTmenuItem * item, char *label,
  int value, Bool isTrigger)
{
  GLUTmenu *menu;

  menu = item->menu;
  item->label = strdup(label);
  if (!item->label)
    __glutFatalError("out of memory.");
  item->isTrigger = isTrigger;
  item->len = (int) strlen(label);
  item->value = value;
  item->pixwidth = XTextWidth(menuFont, label, item->len) + 4;
  if (item->pixwidth > menu->pixwidth) {
    menu->pixwidth = item->pixwidth;
  }
  menu->managed = False;
}

void
glutAddMenuEntry(char *label, int value)
{
  XSetWindowAttributes wa;
  GLUTmenuItem *entry;

  if (__glutMappedMenu)
    menuModificationError();
  entry = (GLUTmenuItem *) malloc(sizeof(GLUTmenuItem));
  if (!entry)
    __glutFatalError("out of memory.");
  entry->menu = __glutCurrentMenu;
  setMenuItem(entry, label, value, False);
  wa.event_mask = EnterWindowMask | LeaveWindowMask;
  entry->win = XCreateWindow(__glutDisplay,
    __glutCurrentMenu->win, MENU_GAP,
    __glutCurrentMenu->num * fontHeight + MENU_GAP,  /* x & y */
    entry->pixwidth, fontHeight,  /* width & height */
    0, CopyFromParent, InputOnly, CopyFromParent,
    CWEventMask, &wa);
  XMapWindow(__glutDisplay, entry->win);
  __glutCurrentMenu->num++;
  entry->next = __glutCurrentMenu->list;
  __glutCurrentMenu->list = entry;
}

void
glutAddSubMenu(char *label, int menu)
{
  XSetWindowAttributes wa;
  GLUTmenuItem *submenu;

  if (__glutMappedMenu)
    menuModificationError();
  submenu = (GLUTmenuItem *) malloc(sizeof(GLUTmenuItem));
  if (!submenu)
    __glutFatalError("out of memory.");
  __glutCurrentMenu->submenus++;
  submenu->menu = __glutCurrentMenu;
  setMenuItem(submenu, label, /* base 0 */ menu - 1, True);
  wa.event_mask = EnterWindowMask | LeaveWindowMask;
  submenu->win = XCreateWindow(__glutDisplay,
    __glutCurrentMenu->win, MENU_GAP,
    __glutCurrentMenu->num * fontHeight + MENU_GAP,  /* x & y */
    submenu->pixwidth, fontHeight,  /* width & height */
    0, CopyFromParent, InputOnly, CopyFromParent,
    CWEventMask, &wa);
  XMapWindow(__glutDisplay, submenu->win);
  __glutCurrentMenu->num++;
  submenu->next = __glutCurrentMenu->list;
  __glutCurrentMenu->list = submenu;
}

void
glutChangeToMenuEntry(int num, char *label, int value)
{
  GLUTmenuItem *item;
  int i;

  if (__glutMappedMenu)
    menuModificationError();
  i = __glutCurrentMenu->num;
  item = __glutCurrentMenu->list;
  while (item) {
    if (i == num) {
      if (item->isTrigger) {
        /* If changing a submenu trigger to a menu entry, we
           need to account for submenus.  */
        item->menu->submenus--;
      }
      free(item->label);
      setMenuItem(item, label, value, False);
      return;
    }
    i--;
    item = item->next;
  }
  __glutWarning("Current menu has no %d item.", num);
}

void
glutChangeToSubMenu(int num, char *label, int menu)
{
  GLUTmenuItem *item;
  int i;

  if (__glutMappedMenu)
    menuModificationError();
  i = __glutCurrentMenu->num;
  item = __glutCurrentMenu->list;
  while (item) {
    if (i == num) {
      if (!item->isTrigger) {
        /* If changing a menu entry to as submenu trigger, we
           need to account for submenus.  */
        item->menu->submenus++;
      }
      free(item->label);
      setMenuItem(item, label, /* base 0 */ menu - 1, True);
      return;
    }
    i--;
    item = item->next;
  }
  __glutWarning("Current menu has no %d item.", num);
}

void
glutRemoveMenuItem(int num)
{
  GLUTmenuItem *item, **prev, *remaining;
  int pixwidth, i;

  if (__glutMappedMenu)
    menuModificationError();
  i = __glutCurrentMenu->num;
  prev = &__glutCurrentMenu->list;
  item = __glutCurrentMenu->list;
  /* If menu item is removed, the menu's pixwidth may need to
     be recomputed. */
  pixwidth = 0;
  while (item) {
    if (i == num) {
      /* If this menu item's pixwidth is as wide as the menu's
         pixwidth, removing this menu item will necessitate
         shrinking the menu's pixwidth. */
      if (item->pixwidth >= __glutCurrentMenu->pixwidth) {
        /* Continue recalculating menu pixwidth, first skipping
           the removed item. */
        remaining = item->next;
        while (remaining) {
          if (remaining->pixwidth > pixwidth) {
            pixwidth = remaining->pixwidth;
          }
          remaining = remaining->next;
        }
      }
      __glutCurrentMenu->num--;
      __glutCurrentMenu->managed = False;
      __glutCurrentMenu->pixwidth = pixwidth;

      /* Patch up menu's item list. */
      *prev = item->next;

      free(item->label);
      free(item);
      return;
    }
    if (item->pixwidth > pixwidth) {
      pixwidth = item->pixwidth;
    }
    i--;
    prev = &item->next;
    item = item->next;
  }
  __glutWarning("Current menu has no %d item.", num);
}

void
glutAttachMenu(int button)
{
  if (__glutMappedMenu)
    menuModificationError();
  if (__glutCurrentWindow->menu[button] < 1) {
    __glutCurrentWindow->buttonUses++;
  }
  __glutChangeWindowEventMask(
    ButtonPressMask | ButtonReleaseMask, True);
  __glutCurrentWindow->menu[button] = __glutCurrentMenu->id + 1;
}

void
glutDetachMenu(int button)
{
  if (__glutMappedMenu)
    menuModificationError();
  if (__glutCurrentWindow->menu[button] > 0) {
    __glutCurrentWindow->buttonUses--;
    __glutChangeWindowEventMask(ButtonPressMask | ButtonReleaseMask,
      __glutCurrentWindow->buttonUses > 0);
    __glutCurrentWindow->menu[button] = 0;
  }
}

void
__glutMenuItemEnterOrLeave(GLUTmenuItem * item,
  int num, int type)
{
  int alreadyUp = 0;

  if (type == EnterNotify) {
    GLUTmenuItem *prevItem = item->menu->highlighted;

    if (prevItem && prevItem != item) {
      /* If there's an already highlighted item in this menu
         that is different from this one (we could be
         re-entering an item with an already cascaded
         submenu!), unhighlight the previous item. */
      item->menu->highlighted = NULL;
      paintMenuItem(prevItem, getMenuItemIndex(prevItem));
    }
    item->menu->highlighted = item;
    __glutItemSelected = item;
    if (item->menu->cascade) {
      if (!item->isTrigger) {
        /* Entered a menu item that is not a submenu trigger,
           so pop down the current submenu cascade of this
           menu.  */
        unmapMenu(item->menu->cascade);
        item->menu->cascade = NULL;
      } else {
        GLUTmenu *submenu = menuList[item->value];

        if (submenu->anchor == item) {
          /* We entered the submenu trigger for the submenu
             that is already up, so don't take down the
             submenu.  */
          alreadyUp = 1;
        } else {
          /* Submenu already popped up for some other submenu
             item of this menu; need to pop down that other
             submenu cascade.  */
          unmapMenu(item->menu->cascade);
          item->menu->cascade = NULL;
        }
      }
    }
    if (!alreadyUp) {
      /* Make sure the menu item gets painted with
         highlighting. */
      paintMenuItem(item, num);
    } else {
      /* If already up, should already be highlighted.  */
    }
  } else {
    /* LeaveNotify: Handle leaving a menu item...  */
    if (item->menu->cascade &&
      item->menu->cascade->anchor == item) {
      /* If there is a submenu casacaded from this item, do not
         change the highlighting on this item upon leaving. */
    } else {
      /* Unhighlight this menu item.  */
      item->menu->highlighted = NULL;
      paintMenuItem(item, num);
    }
    __glutItemSelected = NULL;
  }
  if (item->isTrigger) {
    if (type == EnterNotify && !alreadyUp) {
      GLUTmenu *submenu = menuList[item->value];

      mapMenu(submenu,
        item->menu->x + item->menu->pixwidth +
        MENU_ARROW_GAP + MENU_ARROW_WIDTH +
        MENU_GAP + MENU_BORDER,
        item->menu->y + fontHeight * (num - 1) + MENU_GAP);
      item->menu->cascade = submenu;
      submenu->anchor = item;
    }
  }
}
