commit a00b4c97e6dd47ac8ada094890b515cfe6744607
from: Omar Polo <op@omarpolo.com>
date: Sun Jun 20 14:54:12 2021 UTC

optimize redraw_window

don't redraw the page if no scrolling happened.  There's still need to
``force'' the redraw sometimes, like after a resize or after toggling
olivetti-mode, so add a buffer->force_redraw flag for it.

commit - f9560742eabf2ce27a6204047984be113db92642
commit + a00b4c97e6dd47ac8ada094890b515cfe6744607
blob - d56d1135ac820f016d1e15baa26b4149dfc2dd73
blob + ae84fd1733a499d1c4f7f3d5002172687c81fde2
--- telescope.h
+++ telescope.h
@@ -171,6 +171,10 @@ struct hist {
 
 struct buffer {
 	struct parser		 page;
+
+	size_t			 last_line_off;
+	int			 force_redraw;
+
 	int			 curs_x;
 	int			 curs_y;
 	size_t			 line_off;
blob - dd9149bc39d552f9f124461aee85788c9ef010ad
blob + 82a0fedd736cd241035a1e18f08fabc0f32e5a95
--- ui.c
+++ ui.c
@@ -1352,6 +1352,7 @@ wrap_page(struct buffer *buffer, int width)
 		: buffer->current_line->parent;
 	buffer->current_line = NULL;
 
+	buffer->force_redraw = 1;
 	buffer->curs_y = 0;
 	buffer->line_off = 0;
 
@@ -1518,12 +1519,24 @@ redraw_window(WINDOW *win, int height, struct buffer *
 {
 	struct vline	*vl;
 	int		 l;
+
+	/*
+	 * Don't bother redraw the body if nothing changed.  Cursor
+	 * movements count as "nothing changed" if it hasn't produced
+	 * a scroll.  Ensure that wmove is called though!
+	 */
+	if (!buffer->force_redraw &&
+	    buffer->last_line_off == buffer->line_off)
+		goto end;
 
 	werase(win);
 
 	buffer->line_off = MIN(buffer->line_max-1, buffer->line_off);
+	buffer->force_redraw = 0;
+	buffer->last_line_off = buffer->line_off;
+
 	if (TAILQ_EMPTY(&buffer->head))
-		return;
+		goto end;
 
 	l = 0;
 	vl = nth_line(buffer, buffer->line_off);
@@ -1535,6 +1548,7 @@ redraw_window(WINDOW *win, int height, struct buffer *
 			break;
 	}
 
+end:
 	wmove(win, buffer->curs_y, buffer->curs_x);
 }