[hackers] [scroll] Obey line length while scrolling || Jochen Sprickerhof

[git]

commit 247a9b042655291ab64aa9c43f9e89d820e932ee
Author:     Jochen Sprickerhof <g...@jochen.sprickerhof.de>
AuthorDate: Wed Apr 29 23:46:11 2020 +0200
Commit:     Jochen Sprickerhof <g...@jochen.sprickerhof.de>
CommitDate: Wed Apr 29 23:50:36 2020 +0200

    Obey line length while scrolling

diff --git a/scroll.c b/scroll.c
index 26b0527..9242936 100644
--- a/scroll.c
+++ b/scroll.c
@@ -295,7 +295,7 @@ redraw()
 void
 scrollup(int n)
 {
-       int rows = 2, x, y;
+       int rows = 2, x, y, extra = 0;
        struct line *scrollend = bottom;
 
        if (bottom == NULL)
@@ -306,18 +306,24 @@ scrollup(int n)
        if (n < 0) /* scroll by fraction of ws.ws_row, but at least one line */
                n = ws.ws_row > (-n) ? ws.ws_row / (-n) : 1;
 
-       /* wind back scrollend pointer by one page plus n */
-       for (; TAILQ_NEXT(scrollend, entries) != NULL &&
-           rows < y + n; rows++)
+       /* wind back scrollend pointer by the current screen */
+       while (rows < y && TAILQ_NEXT(scrollend, entries) != NULL) {
                scrollend = TAILQ_NEXT(scrollend, entries);
-
-       rows -= y;
+               rows += (scrollend->len - 1) / ws.ws_col + 1;
+       }
 
        if (rows <= 0)
                return;
 
+       /* wind back scrollend pointer n lines */
+       for (rows = 0; rows + extra < n &&
+           TAILQ_NEXT(scrollend, entries) != NULL; rows++) {
+               scrollend = TAILQ_NEXT(scrollend, entries);
+               extra += (scrollend->len - 1) / ws.ws_col;
+       }
+
        /* move the text in terminal rows lines down */
-       dprintf(STDOUT_FILENO, "\033[%dT", rows);
+       dprintf(STDOUT_FILENO, "\033[%dT", n);
        /* set cursor position to upper left corner */
        write(STDOUT_FILENO, "\033[0;0H", 6);
        /* hide cursor */
@@ -357,9 +363,10 @@ scrolldown(char *buf, size_t size, int n)
 
        bottom = TAILQ_PREV(bottom, tailhead, entries);
        /* print n lines */
-       for (; n > 0 && bottom != NULL && bottom != TAILQ_FIRST(&head); n--) {
+       while (n > 0 && bottom != NULL && bottom != TAILQ_FIRST(&head)) {
                bottom = TAILQ_PREV(bottom, tailhead, entries);
                write(STDOUT_FILENO, bottom->buf, bottom->size);
+               n -= (bottom->len - 1) / ws.ws_col + 1;
        }
        if (n > 0 && bottom == TAILQ_FIRST(&head)) {
                write(STDOUT_FILENO, "\033[?25h", 6);   /* show cursor */