top: normalize vertical scrolling for hidden processes

To my knowledge, nobody has ever complained about some
anomalies when scrolling vertically if tasks should be
hidden from view. This can happen with the user filter
('u/U') or other filter ('o/O') features. And although
some tasks are not shown, they still impact scrolling.

This is most apparent when that scroll coordinates msg
is on ('C') & up/down arrow keys used (vs. pgup/pgdn).

Now that we can collapse/expand forked children, there
is a potential for yet more of those hidden processes.

So this commit normalizes vertical scrolling providing
an expected behavior. In other words, the up/down keys
skip the unseen tasks to reposition on a visible task.

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

top/top.c

@@ -3919,9 +3919,9 @@ static void win_names (WIN_t *q, const char *name) {
 static void win_reset (WIN_t *q) {
          SETw(q, Show_IDLEPS | Show_TASKON);
 #ifndef SCROLLVAR_NO
-         q->rc.maxtasks = q->usrseltyp = q->begpflg = q->begtask = q->varcolbeg = 0;
+         q->rc.maxtasks = q->usrseltyp = q->begpflg = q->begtask = q->begnext = q->varcolbeg = 0;
 #else
-         q->rc.maxtasks = q->usrseltyp = q->begpflg = q->begtask = 0;
+         q->rc.maxtasks = q->usrseltyp = q->begpflg = q->begtask = q->begnext = 0;
 #endif
          Monpidsidx = 0;
          osel_clear(q);
@@ -4408,7 +4408,7 @@ static void find_string (int ch) {
 #endif
    }
    if (Curwin->findstr[0]) {
-      SETw(Curwin, INFINDS_xxx);
+      SETw(Curwin, NOPRINT_xxx);
       for (i = Curwin->begtask; i < PIDSmaxt; i++) {
          const char *row = task_show(Curwin, Curwin->ppt[i]);
          if (*row && -1 < find_ofs(Curwin, row)) {
@@ -4990,10 +4990,10 @@ static void keys_window (int ch) {
          }
          break;
       case kbd_UP:
-         if (VIZCHKw(w)) if (CHKw(w, Show_IDLEPS) && 0 < w->begtask) w->begtask -= 1;
+         if (VIZCHKw(w)) if (CHKw(w, Show_IDLEPS)) w->begnext = -1;
          break;
       case kbd_DOWN:
-         if (VIZCHKw(w)) if (CHKw(w, Show_IDLEPS) && (w->begtask < PIDSmaxt - 1)) w->begtask += 1;
+         if (VIZCHKw(w)) if (CHKw(w, Show_IDLEPS)) w->begnext = +1;
          break;
 #ifdef USE_X_COLHDR // ------------------------------------
       case kbd_LEFT:
@@ -5063,17 +5063,14 @@ static void keys_window (int ch) {
       case kbd_PGUP:
          if (VIZCHKw(w)) {
             if (CHKw(w, Show_IDLEPS) && 0 < w->begtask) {
-               w->begtask -= (w->winlines - 1);
+               w->begnext = -(w->winlines - 1);
-               if (0 > w->begtask) w->begtask = 0;
             }
          }
          break;
       case kbd_PGDN:
          if (VIZCHKw(w)) {
             if (CHKw(w, Show_IDLEPS) && w->begtask < PIDSmaxt - 1) {
-               w->begtask += (w->winlines - 1);
+               w->begnext = +(w->winlines - 1);
-               if (w->begtask > PIDSmaxt - 1) w->begtask = PIDSmaxt - 1;
-               if (0 > w->begtask) w->begtask = 0;
             }
          }
          break;
@@ -5087,8 +5084,7 @@ static void keys_window (int ch) {
       case kbd_END:
          if (VIZCHKw(w)) {
             if (CHKw(w, Show_IDLEPS)) {
-               w->begtask = (PIDSmaxt - w->winlines) + 1;
+               w->begnext = (PIDSmaxt - w->winlines) + 1;
-               if (0 > w->begtask) w->begtask = 0;
                w->begpflg = w->endpflg;
 #ifndef SCROLLVAR_NO
                w->varcolbeg = 0;
@@ -5507,7 +5503,7 @@ static const char *task_show (const WIN_t *q, struct pids_stack *p) {
          case EU_XOF:
          case EU_XON:
             cp = NULL;
-            if (!CHKw(q, INFINDS_xxx | NOHIFND_xxx | NOHISEL_xxx)) {
+            if (!CHKw(q, NOPRINT_xxx | NOHIFND_xxx | NOHISEL_xxx)) {
                /* treat running tasks specially - entire row may get highlighted
                   so we needn't turn it on and we MUST NOT turn it off */
                if (!('R' == rSv(EU_STA, s_ch) && CHKw(q, Show_HIROWS)))
@@ -5662,7 +5658,7 @@ static const char *task_show (const WIN_t *q, struct pids_stack *p) {
       #undef Jn
    } // end: for 'maxpflgs'
 
-   if (!CHKw(q, INFINDS_xxx)) {
+   if (!CHKw(q, NOPRINT_xxx)) {
       const char *cap = ((CHKw(q, Show_HIROWS) && 'R' == rSv(EU_STA, s_ch)))
          ? q->capclr_rowhigh : q->capclr_rownorm;
       char *row = rbuf;
@@ -5693,6 +5689,51 @@ static const char *task_show (const WIN_t *q, struct pids_stack *p) {
 } // end: task_show
 
 
+        /*
+         * 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 */
+static void window_hlp (void) {
+   WIN_t *w = Curwin;             // avoid gcc bloat with a local copy
+   int i;
+
+   SETw(w, NOPRINT_xxx);
+   w->begtask += w->begnext;
+   if (w->begtask < 0) w->begtask = 0;
+   if (w->begtask >= PIDSmaxt) w->begtask = PIDSmaxt - 1;
+
+   // potentially scroll forward ...
+   if (w->begnext > 0) {
+      for (i = w->begtask; i < PIDSmaxt; i++) {
+         if (wins_usrselect(w, w->ppt[i])
+         && (*task_show(w, w->ppt[i])))
+            break;
+      }
+      if (i < PIDSmaxt) {
+         w->begtask = i;
+         goto wrap_up;
+      }
+      // no luck forward, so let's try backward
+      w->begtask = PIDSmaxt - 1;
+   }
+
+   // potentially scroll backward ...
+   for (i = w->begtask; i > 0; i--) {
+      if (wins_usrselect(w, w->ppt[i])
+      && (*task_show(w, w->ppt[i])))
+         break;
+   }
+   w->begtask = i;
+
+wrap_up:
+   w->begnext = 0;
+   OFFw(w, NOPRINT_xxx);
+} // end: window_hlp
+
+
 static int window_show (WIN_t *q, int wmax) {
  #define sORDER  CHKw(q, Qsrt_NORMAL) ? PIDS_SORT_DESCEND : PIDS_SORT_ASCEND
  /* the isBUSY macro determines if a task is 'active' --
@@ -5717,6 +5758,9 @@ static int window_show (WIN_t *q, int wmax) {
          error_exit(fmtmk(N_fmt(LIB_errorpid_fmt),__LINE__, strerror(errno)));
    }
 
+   if (q->begnext) window_hlp();
+   else OFFw(q, NOPRINT_xxx);
+
    i = q->begtask;
    lwin = 1;                                        // 1 for the column header
    wmax = winMIN(wmax, q->winlines + 1);            // ditto for winlines, too
@@ -5807,7 +5851,6 @@ static void frame_make (void) {
    Tree_idx = Pseudo_row = Msg_row = scrlins = 0;
    summary_show();
    Max_lines = (Screen_rows - Msg_row) - 1;
-   OFFw(w, INFINDS_xxx);
 
    // we're now on Msg_row so clear out any residual messages ...
    putp(Cap_clr_eol);

top/top.h

@@ -245,7 +245,7 @@ typedef          long long SIC_t;
 #define Show_JRSTRS  0x040000     // 'j' - right justify "string" data cols
 #define Show_JRNUMS  0x020000     // 'J' - right justify "numeric" data cols
         // these flag(s) have no command as such - they're for internal use
-#define INFINDS_xxx  0x010000     // build rows for find_string, not display
+#define NOPRINT_xxx  0x010000     // build task rows only (not for display)
 #define EQUWINS_xxx  0x000001     // rebalance all wins & tasks (off i,n,u/U)
 #ifndef USE_X_COLHDR
 #define NOHISEL_xxx  0x200000     // restrict Show_HICOLS for osel temporarily
@@ -325,6 +325,7 @@ typedef struct WIN_t {
           begpflg,         // scrolled beginning pos into pflgsall array
           endpflg,         // scrolled ending pos into pflgsall array
           begtask,         // scrolled beginning pos into total tasks
+          begnext,         // new scrolled delta for next frame's begtask
 #ifndef SCROLLVAR_NO
           varcolbeg,       // scrolled position within variable width col
 #endif
@@ -665,6 +666,7 @@ typedef struct WIN_t {
 //atic void          summary_hlp (struct stat_stack *this, const char *pfx);
 //atic void          summary_show (void);
 //atic const char   *task_show (const WIN_t *q, struct pids_stack *p);
+//atic void          window_hlp (void);
 //atic int           window_show (WIN_t *q, int wmax);
 /*------  Entry point plus two  ------------------------------------------*/
 //atic void          frame_hlp (int wix, int max);