top: provide for avoiding task focus ('F') distortions

In the patch referenced below the focus task logic was
improved to ensure that newly cloned tasks 'above' the
focused task did not force an effect like the up arrow
key. That commit also acknowledged that when some task
'above' ended, it *would* act like the down arrow key.

Well, with this commit a task ending 'above' a focused
task no longer distorts the focus. That's assuming the
new '#define FOCUS_HARD_Y' is specified plus the total
focused tasks does not exceed the current screen rows.

Thus, the manual scrolling with up and down arrow keys
is allowed when the total focused exceeds screen rows.

[ but keep in mind that when a focused task has been ]
[ hardened some otherwise useful toggles will not be ]
[ available. keystrokes like 'v' and even 'F' itself ]
[ can not be applied to another task with no scroll. ]

Reference(s):
. Sep, 2021 - 'focus' logic improved
commit 69978e3650

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

top/top.c

@@ -4625,7 +4625,7 @@ static void forest_config (WIN_t *q) {
    if (i == PIDSmaxt)
       q->focus_pid = q->begtask = 0;
    else {
-#ifdef TREE_FOCUS_X
+#ifdef FOCUS_TREE_X
       q->focus_lvl = rSv(i);
 #endif
       while (i+1 < PIDSmaxt && rSv(i+1) > level)
@@ -4636,6 +4636,15 @@ static void forest_config (WIN_t *q) {
          q->begtask = q->focus_beg;
          q->begnext = 0;     // as 'mkVIZoff' but in any window
       }
+#ifdef FOCUS_HARD_Y
+      // if some task 'above' us ended, try to maintain focus
+      // ( but allow scrolling when there are many children )
+      if (q->begtask > q->focus_beg
+      && (Screen_rows > (q->focus_end - q->focus_beg))) {
+         q->begtask = q->focus_beg;
+         q->begnext = 0;     // as 'mkVIZoff' but in any window
+      }
+#endif
    }
  #undef rSv
 } // end: forest_config
@@ -4658,7 +4667,7 @@ static inline const char *forest_display (const WIN_t *q, int idx) {
    const char *which = (CHKw(q, Show_CMDLIN)) ? rSv(eu_CMDLINE) : rSv(EU_CMD);
    int level = rSv_Lvl;
 
-#ifdef TREE_FOCUS_X
+#ifdef FOCUS_TREE_X
    if (q->focus_pid) {
       if (idx >= q->focus_beg && idx < q->focus_end)
          level -= q->focus_lvl;

top/top.h

@@ -29,6 +29,8 @@
 //#define CASEUP_HEXES            /* show all those hex values in upper case */
 //#define CASEUP_SUFIX            /* show time/mem/cnts suffix in upper case */
 //#define EQUCOLHDRYES            /* yes, equalize the column header lengths */
+//#define FOCUS_HARD_Y            /* 'F' will avoid topmost task distortions */
+//#define FOCUS_TREE_X            /* 'F' resets forest view indentation to 0 */
 //#define GETOPTFIX_NO            /* do not address getopt_long deficiencies */
 //#define INSP_JUSTNOT            /* do not smooth unprintable right margins */
 //#define INSP_OFFDEMO            /* disable demo screens, issue msg instead */
@@ -57,7 +59,6 @@
 //#define TOG4_NOTRUNC            /* ensure no truncation for 2 abreast mode */
 //#define TOG4_OFF_MEM            /* don't show two abreast memory statistic */
 //#define TOG4_OFF_SEP            /* don't show two abreast visual separator */
-//#define TREE_FOCUS_X            /* 'F' resets forest view indentation to 0 */
 //#define TREE_NORESET            /* sort keys should not force 'V' view off */
 //#define TREE_SCANALL            /* rescan array w/ forest view, avoid sort */
 //#define TREE_VALTMRK            /* use an indented '+' with collapsed pids */
@@ -373,7 +374,7 @@ typedef struct WIN_t {
    int    focus_pid;                   // target pid when 'F' toggle is active
    int    focus_beg;                   // ppt index where 'F' toggle has begun
    int    focus_end;                   // ppt index where 'F' toggle has ended
-#ifdef TREE_FOCUS_X
+#ifdef FOCUS_TREE_X
    int    focus_lvl;                   // the indentation level of parent task
 #endif
    struct pids_stack **ppt;            // this window's stacks ptr array