[hackers] [scroll] Rework scrollup to accept n, lines to scroll || Jochen Sprickerhof

[git]

commit eec2eca605ddcf8f3774e702d405736d798a8d32
Author:     Jochen Sprickerhof <g...@jochen.sprickerhof.de>
AuthorDate: Sat Apr 4 20:15:24 2020 +0200
Commit:     Jochen Sprickerhof <g...@jochen.sprickerhof.de>
CommitDate: Sat Apr 4 20:15:59 2020 +0200

    Rework scrollup to accept n, lines to scroll

diff --git a/scroll.c b/scroll.c
index ceed4ef..4c77654 100644
--- a/scroll.c
+++ b/scroll.c
@@ -249,38 +249,40 @@ addline(char *buf, size_t size)
 }
 
 void
-scrollup(void)
+scrollup(int n)
 {
-       int rows = - ws.ws_row + 1;
-       struct line *bottom_old = bottom;
+       int rows = 2;
+       struct line *scrollend = bottom;
 
-       /* account for last line */
-       if (bottom != NULL && TAILQ_PREV(bottom, tailhead, entries) == NULL)
-               rows++;
+       /* wind back scrollend pointer by one page plus n */
+       for (; scrollend != NULL && TAILQ_NEXT(scrollend, entries) != NULL &&
+           rows < ws.ws_row + n; rows++)
+               scrollend = TAILQ_NEXT(scrollend, entries);
 
-       /* wind back bottom pointer by two pages */
-       for (; bottom != NULL && TAILQ_NEXT(bottom, entries) != NULL &&
-           rows <= ws.ws_row; rows++)
-               bottom = TAILQ_NEXT(bottom, entries);
+       rows -= ws.ws_row;
 
        if (rows <= 0) {
-               bottom = bottom_old;
                return;
        }
 
-       /* move the text in terminal n lines down */
+       /* move the text in terminal rows lines down */
        dprintf(STDOUT_FILENO, "\033[%dT", rows);
        /* set cursor position to upper left corner */
        write(STDOUT_FILENO, "\033[0;0H", 6);
        /* hide cursor */
        write(STDOUT_FILENO, "\033[?25l", 6);
 
-       /* print one page */
-       for (; rows > 0; rows--) {
-               write(STDOUT_FILENO, bottom->buf, bottom->size);
-               bottom = TAILQ_PREV(bottom, tailhead, entries);
-       }
+       /* remove newline of first line as we are at 0,0 already */
+       if (scrollend->size > 2)
+               write(STDOUT_FILENO, scrollend->buf + 2, scrollend->size - 2);
        bottom = TAILQ_NEXT(bottom, entries);
+
+       /* print rows lines and move bottom forward to the new screen bottom */
+       for (; rows > 1; rows--) {
+               scrollend = TAILQ_PREV(scrollend, tailhead, entries);
+               bottom = TAILQ_NEXT(bottom, entries);
+               write(STDOUT_FILENO, scrollend->buf, scrollend->size);
+       }
 }
 
 void
@@ -389,10 +391,10 @@ main(int argc, char *argv[])
                        if (n <= 0 && errno != EINTR)
                                die("read:");
 
-                       if (!altscreen &&
-                           (strncmp(KB_SCROLL_UP, input, n) == 0 ||
-                           strncmp(MS_SCROLL_UP, input, n) == 0))
-                               scrollup();
+                       if (!altscreen && strncmp(KB_SCROLL_UP, input, n) == 0)
+                               scrollup(ws.ws_row);
+                       else if (!altscreen && strncmp(MS_SCROLL_UP, input, n) 
== 0)
+                               scrollup(1);
                        else if (!altscreen &&
                            (strncmp(KB_SCROLL_DOWN, input, n) == 0 ||
                            strncmp(MS_SCROLL_DOWN, input, n) == 0))