From 91d112bf12789da07e25ed001f7961b1d6bd7a76 Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Mon, 18 Jan 2021 10:27:54 +0000
Subject: There is no need to clear every line entirely before drawing to it,
 this means moving the cursor and messes up wrapping. Better to just clear the
 sections that aren't written over. GitHub issue 2537.

---
 screen-write.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

(limited to 'screen-write.c')

diff --git a/screen-write.c b/screen-write.c
index 92f1aa39..7df5cd92 100644
--- a/screen-write.c
+++ b/screen-write.c
@@ -259,7 +259,6 @@ screen_write_start_callback(struct screen_write_ctx *ctx, struct screen *s,
 	}
 }
 
-
 /* Initialize writing. */
 void
 screen_write_start(struct screen_write_ctx *ctx, struct screen *s)
@@ -1517,6 +1516,7 @@ screen_write_collect_flush(struct screen_write_ctx *ctx, int scroll_only,
 	struct screen_write_collect_item	*ci, *tmp;
 	struct screen_write_collect_line	*cl;
 	u_int					 y, cx, cy, items = 0;
+	int					 clear = 0;
 	struct tty_ctx				 ttyctx;
 	size_t					 written = 0;
 
@@ -1540,22 +1540,29 @@ screen_write_collect_flush(struct screen_write_ctx *ctx, int scroll_only,
 	cx = s->cx; cy = s->cy;
 	for (y = 0; y < screen_size_y(s); y++) {
 		cl = &ctx->s->write_list[y];
-		if (cl->bg != 0) {
-			screen_write_set_cursor(ctx, 0, y);
-			screen_write_initctx(ctx, &ttyctx, 1);
-			ttyctx.bg = cl->bg - 1;
-			tty_write(tty_cmd_clearline, &ttyctx);
-		}
 		TAILQ_FOREACH_SAFE(ci, &cl->items, entry, tmp) {
+			if (clear != -1 &&
+			    (u_int)clear != ci->x &&
+			    cl->bg != 0) {
+				screen_write_set_cursor(ctx, clear, y);
+				screen_write_initctx(ctx, &ttyctx, 1);
+				ttyctx.bg = cl->bg - 1;
+				ttyctx.num = ci->x - clear;
+				log_debug("clear %u at %u", ttyctx.num, clear);
+				tty_write(tty_cmd_clearcharacter, &ttyctx);
+			}
+
 			screen_write_set_cursor(ctx, ci->x, y);
 			if (ci->type == CLEAR_END) {
 				screen_write_initctx(ctx, &ttyctx, 1);
 				ttyctx.bg = ci->bg;
 				tty_write(tty_cmd_clearendofline, &ttyctx);
+				clear = -1;
 			} else if (ci->type == CLEAR_START) {
 				screen_write_initctx(ctx, &ttyctx, 1);
 				ttyctx.bg = ci->bg;
 				tty_write(tty_cmd_clearstartofline, &ttyctx);
+				clear = ci->x + 1;
 			} else {
 				screen_write_initctx(ctx, &ttyctx, 0);
 				ttyctx.cell = &ci->gc;
@@ -1563,6 +1570,7 @@ screen_write_collect_flush(struct screen_write_ctx *ctx, int scroll_only,
 				ttyctx.ptr = cl->data + ci->x;
 				ttyctx.num = ci->used;
 				tty_write(tty_cmd_cells, &ttyctx);
+				clear = ci->x + ci->used;
 			}
 
 			items++;
@@ -1571,6 +1579,16 @@ screen_write_collect_flush(struct screen_write_ctx *ctx, int scroll_only,
 			TAILQ_REMOVE(&cl->items, ci, entry);
 			free(ci);
 		}
+		if (clear != -1 &&
+		    (u_int)clear != screen_size_x(s) - 1 &&
+		    cl->bg != 0) {
+			screen_write_set_cursor(ctx, clear, y);
+			screen_write_initctx(ctx, &ttyctx, 1);
+			ttyctx.bg = cl->bg - 1;
+			log_debug("clear to end at %u", clear);
+			tty_write(tty_cmd_clearendofline, &ttyctx);
+		}
+		clear = 0;
 		cl->bg = 0;
 	}
 	s->cx = cx; s->cy = cy;
-- 
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