From 9d59ddc4661453dc65a8fc81dd75bfea40b7696c Mon Sep 17 00:00:00 2001
From: Jim Warner <james.warner@comcast.net>
Date: Thu, 21 Jun 2018 00:00:00 -0500
Subject: [PATCH] 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 | 36 +++++++++++++++++++++++++++---------
 top/top.h |  4 ++++
 2 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/top/top.c b/top/top.c
index 5fed17d6..78510172 100644
--- a/top/top.c
+++ b/top/top.c
@@ -3957,7 +3957,9 @@ static WIN_t *win_select (int ch) {
       default:                    // keep gcc happy
          break;
    }
-   return Curwin = w;
+   Curwin = w;
+   mkVIZrow1(Curwin);
+   return Curwin;
 } // end: win_select
 
 
@@ -4184,6 +4186,9 @@ static void wins_stage_2 (void) {
    // fill in missing Fieldstab members and build each window's columnhdr
    zap_fieldstab();
 
+   // 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
@@ -4940,7 +4945,7 @@ 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;
@@ -5077,8 +5082,10 @@ 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:
@@ -5693,20 +5700,24 @@ static const char *task_show (const WIN_t *q, struct pids_stack *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 >= PIDSmaxt) w->begtask = PIDSmaxt - 1;
+   // next 'if' will force a forward scan ...
+   if (w->begtask <= 0) { w->begtask = 0; w->begnext = +1; }
+   else if (w->begtask >= PIDSmaxt) w->begtask = PIDSmaxt - 1;
 
+   reversed = 0;
    // potentially scroll forward ...
    if (w->begnext > 0) {
+fwd_redux:
       for (i = w->begtask; i < PIDSmaxt; i++) {
          if (wins_usrselect(w, w->ppt[i])
          && (*task_show(w, w->ppt[i])))
@@ -5726,7 +5737,14 @@ 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 (!(wins_usrselect(w, w->ppt[0]))
+      || (!(*task_show(w, w->ppt[0])))) {
+         reversed = 1;
+         goto fwd_redux;
+      }
+   }
 
 wrap_up:
    w->begnext = 0;
diff --git a/top/top.h b/top/top.h
index 3bbdba83..7eca5f2d 100644
--- a/top/top.h
+++ b/top/top.h
@@ -388,6 +388,10 @@ 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 ------------------------------------------ */
         /* /////////////////////////////////////////////////////////////// */