top: a few tweaks for those scrolling (mostly) changes

This patch just addresses some edge cases with respect
to 'unseen' tasks. Given the ability to preserve other
filters in the rcfile, it's entirely possible the very
first task(s) may not be visible at top startup. Also,
when switching between windows ('a'/'w') we should try
to always position its row #1 on some visible process.

Lastly, a window might have *NO* visible tasks at all.
Therefore, protect 'window_hlp' from an infinite loop.

Signed-off-by: Jim Warner <james.warner@comcast.net>

top/top.c

@@ -4424,7 +4424,9 @@ static WIN_t *win_select (int ch) {
       default:                    // keep gcc happy
          break;
    }
-   return Curwin = w;
+   Curwin = w;
+   mkVIZrow1(Curwin);
+   return Curwin;
 } // end: win_select
 
 
@@ -4662,6 +4664,9 @@ static void wins_stage_2 (void) {
       ;                           // avoid -Wunused-result
 #endif
 
+   // with preserved 'other filters', ensure a visible task on row #1
+   mkVIZrow1(Curwin);
+
    // lastly, initialize a signal set used to throttle one troublesome signal
    sigemptyset(&Sigwinch_set);
 #ifdef SIGNALS_LESS
@@ -4788,7 +4793,7 @@ static inline const char *forest_display (const WIN_t *q, const proc_t *p) {
 
    if (!CHKw(q, Show_FOREST) || !p->pad_3) return which;
 #ifndef TREE_VWINALL
-   if (q == Curwin)
+   if (q == Curwin)            // note: the following is NOT indented
 #endif
    if (p->pad_2 == 'x') {
       snprintf(buf, sizeof(buf), "+%*s%s", ((4 * p->pad_3) - 1), "`- ", which);
@@ -5380,7 +5385,7 @@ static void keys_task (int ch) {
                   }
                }
                if (i == Hide_tot) Hide_pid[Hide_tot++] = pid;
-               // plenty of room, but if everything's expaned let's reset ...
+               // plenty of room, but if everything's expanded let's reset ...
                for (i = 0; i < Hide_tot; i++)
                   if (Hide_pid[i] > 0) break;
                if (i == Hide_tot) Hide_tot = 0;
@@ -5517,8 +5522,10 @@ static void keys_window (int ch) {
       case kbd_HOME:
 #ifndef SCROLLVAR_NO
          if (VIZCHKw(w)) if (CHKw(w, Show_IDLEPS)) w->begtask = w->begpflg = w->varcolbeg = 0;
+         mkVIZrow1(w);
 #else
          if (VIZCHKw(w)) if (CHKw(w, Show_IDLEPS)) w->begtask = w->begpflg = 0;
+         mkVIZrow1(w);
 #endif
          break;
       case kbd_END:
@@ -5931,7 +5938,7 @@ static const char *task_show (const WIN_t *q, const proc_t *p) {
       pad_2: 'x' means a collapsed thread, 'z' means an unseen child
       pad_3: where level number is stored (0 - 100) */
 #ifndef TREE_VWINALL
-   if (q == Curwin)
+   if (q == Curwin)            // note: the following is NOT indented
 #endif
    if (CHKw(q, Show_FOREST) && p->pad_2 == 'z')
       return "";
@@ -6191,20 +6198,24 @@ static const char *task_show (const WIN_t *q, const proc_t *p) {
          * A window_show *Helper* function ensuring that Curwin's 'begtask'
          * represents a visible process (not any hidden/filtered-out task).
          * In reality, this function is called:
-         *   1) exclusively for the current window
-         *   2) immediately after interacting with a user
-         *   3) with the only key stuck: up, down, pgup, pgdn or end */
+         *   1) exclusively for the 'current' window
+         *   2) immediately after interacting with the user
+         *   3) who struck 1 of these: up, down, pgup, pgdn, home or end
+         *   4) or upon the user switching from one window to another window */
 static void window_hlp (void) {
    WIN_t *w = Curwin;             // avoid gcc bloat with a local copy
-   int i;
+   int i, reversed;
 
    SETw(w, NOPRINT_xxx);
    w->begtask += w->begnext;
-   if (w->begtask < 0) w->begtask = 0;
-   if (w->begtask >= Frame_maxtask) w->begtask = Frame_maxtask - 1;
+   // next 'if' will force a forward scan ...
+   if (w->begtask <= 0) { w->begtask = 0; w->begnext = +1; }
+   else if (w->begtask >= Frame_maxtask) w->begtask = Frame_maxtask - 1;
 
+   reversed = 0;
    // potentially scroll forward ...
    if (w->begnext > 0) {
+fwd_redux:
       for (i = w->begtask; i < Frame_maxtask; i++) {
          if (user_matched(w, w->ppt[i])
          && (*task_show(w, w->ppt[i])))
@@ -6224,7 +6235,14 @@ static void window_hlp (void) {
       && (*task_show(w, w->ppt[i])))
          break;
    }
-   w->begtask = i;
+   // reached the top, but maybe this guy ain't visible
+   if (!(w->begtask = i) && !reversed) {
+      if (!(user_matched(w, w->ppt[0]))
+      || (!(*task_show(w, w->ppt[0])))) {
+         reversed = 1;
+         goto fwd_redux;
+      }
+   }
 
 wrap_up:
    w->begnext = 0;

top/top.h

@@ -474,6 +474,10 @@ typedef struct WIN_t {
 #define SCROLLAMT    8
 #endif
 
+        // Support for a proper (visible) row #1 whenever Curwin changes
+        // ( or a certain vertical scrolling key has been struck )
+#define mkVIZrow1(q) { q->begtask -= 1; q->begnext = +1; }
+
         /* Special Section: end ------------------------------------------ */
         /* /////////////////////////////////////////////////////////////// */