commit 94ec38e85dbc4ec718934b3bcc765398e2b8ccd4
from: Omar Polo <op@omarpolo.com>
date: Tue Jun 29 18:44:37 2021 UTC

optimisation: cache the top_line vline

instead of using the line_off + vline_nth, cache the current top line.

commit - 60e7ebd308ed9ece004eb91f81feb9343e589334
commit + 94ec38e85dbc4ec718934b3bcc765398e2b8ccd4
blob - 4d64069ea7d59c6276e1dbe0ff26a8dbbb8c533a
blob + b5cff45710f8bacfe9d23f92805d6e7fe19748f0
--- cmd.c
+++ cmd.c
@@ -141,6 +141,7 @@ cmd_scroll_line_up(struct buffer *buffer)
 		return;
 
 	buffer->line_off--;
+	buffer->top_line = TAILQ_PREV(buffer->top_line, vhead, vlines);
 	buffer->current_line = TAILQ_PREV(buffer->current_line, vhead, vlines);
 	restore_cursor(buffer);
 }
@@ -157,7 +158,10 @@ cmd_scroll_line_down(struct buffer *buffer)
 		return;
 
 	buffer->current_line = vl;
+
+	buffer->top_line = TAILQ_NEXT(buffer->top_line, vlines);
 	buffer->line_off++;
+
 	restore_cursor(buffer);
 }
 
@@ -187,6 +191,7 @@ void
 cmd_beginning_of_buffer(struct buffer *buffer)
 {
 	buffer->current_line = TAILQ_FIRST(&buffer->head);
+	buffer->top_line = buffer->current_line;
 	buffer->line_off = 0;
 	buffer->curs_y = 0;
 	buffer->cpoff = 0;
@@ -200,6 +205,15 @@ cmd_end_of_buffer(struct buffer *buffer)
 
 	off = buffer->line_max - body_lines;
 	off = MAX(0, off);
+
+	while (buffer->line_off > (size_t)off) {
+		buffer->line_off--;
+		buffer->top_line = TAILQ_PREV(buffer->top_line, vhead, vlines);
+	}
+	while (buffer->line_off < (size_t)off) {
+		buffer->line_off++;
+		buffer->top_line = TAILQ_NEXT(buffer->top_line, vlines);
+	}
 
 	buffer->line_off = off;
 	buffer->curs_y = MIN((size_t)body_lines-1, buffer->line_max-1);
blob - d1627087376d67b890105acc9638195bb0c13202
blob + 8ba69fbf498995de86497b1f3d19c5b144c6abff
--- telescope.h
+++ telescope.h
@@ -200,6 +200,7 @@ struct buffer {
 	int			 curs_y;
 	size_t			 line_off;
 	size_t			 line_max;
+	struct vline		*top_line;
 	struct vline		*current_line;
 	size_t			 cpoff;
 	TAILQ_HEAD(vhead, vline) head;
blob - 919c538e2658fe1a8347a999c4faea6e64c819ba
blob + 2b0cc30aa67a7e932f2f09f29e4896693dd2c3dc
--- ui.c
+++ ui.c
@@ -568,9 +568,9 @@ wrap_page(struct buffer *buffer, int width)
 	int			 pre_width;
 	const char		*prfx;
 
-	orig = buffer->current_line == NULL
-		? NULL
-		: buffer->current_line->parent;
+	orig = buffer->current_line == NULL ? NULL : buffer->current_line->parent;
+
+	buffer->top_line = NULL;
 	buffer->current_line = NULL;
 
 	buffer->force_redraw = 1;
@@ -619,6 +619,8 @@ wrap_page(struct buffer *buffer, int width)
         if (buffer->current_line == NULL)
 		buffer->current_line = TAILQ_FIRST(&buffer->head);
 
+	buffer->top_line = buffer->current_line;
+
 	return 1;
 }
 
@@ -792,8 +794,7 @@ redraw_window(WINDOW *win, int height, int width, stru
 		goto end;
 
 	l = 0;
-	vl = nth_line(buffer, buffer->line_off);
-	for (; vl != NULL; vl = TAILQ_NEXT(vl, vlines)) {
+	for (vl = buffer->top_line; vl != NULL; vl = TAILQ_NEXT(vl, vlines)) {
 		wmove(win, l, 0);
 		print_vline(x_offset, width, win, vl);
 		l++;