From a42df2434b796f19ff729e194dd6a22f5128b89a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Tue, 29 Oct 2019 21:09:37 +0100
Subject: [PATCH] scrollback: regression: fix rendering of scrollback diffs
 less than a screen

When doing "small" scrolls (typically done via mouse wheel or
similar), we render the scrolling by emitting a "scroll damage".

A recent commit changed how scroll damage is rendered; only when the
view is at the bottom ("following" the screen output) do we render the
damage.

To fix this, add a new type of scroll damage,
SCROLL_DAMAGE_IN_VIEW and SCROLL_DAMAGE_REVERSE_IN_VIEW.

These signal to the renderer that it should always render the damage.
---
 commands.c |  4 ++--
 render.c   | 29 ++++++++++++++++++-----------
 terminal.h |  4 +++-
 3 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/commands.c b/commands.c
index 01e73981..5d20b94b 100644
--- a/commands.c
+++ b/commands.c
@@ -72,7 +72,7 @@ cmd_scrollback_up(struct terminal *term, int rows)
     term->grid->view = new_view;
 
     if (diff >= 0 && diff < term->rows) {
-        term_damage_scroll(term, DAMAGE_SCROLL_REVERSE, (struct scroll_region){0, term->rows}, diff);
+        term_damage_scroll(term, DAMAGE_SCROLL_REVERSE_IN_VIEW, (struct scroll_region){0, term->rows}, diff);
         term_damage_rows_in_view(term, 0, diff - 1);
     } else
         term_damage_view(term);
@@ -142,7 +142,7 @@ cmd_scrollback_down(struct terminal *term, int rows)
     term->grid->view = new_view;
 
     if (diff >= 0 && diff < term->rows) {
-        term_damage_scroll(term, DAMAGE_SCROLL, (struct scroll_region){0, term->rows}, diff);
+        term_damage_scroll(term, DAMAGE_SCROLL_IN_VIEW, (struct scroll_region){0, term->rows}, diff);
         term_damage_rows_in_view(term, term->rows - diff, term->rows - 1);
     } else
         term_damage_view(term);
diff --git a/render.c b/render.c
index de5c2246..ca127389 100644
--- a/render.c
+++ b/render.c
@@ -530,22 +530,29 @@ grid_render(struct terminal *term)
         }
     }
 
-    if (term->grid->view == term->grid->offset) {
-        tll_foreach(term->grid->scroll_damage, it) {
-            switch (it->item.type) {
-            case DAMAGE_SCROLL:
+    tll_foreach(term->grid->scroll_damage, it) {
+        switch (it->item.type) {
+        case DAMAGE_SCROLL:
+            if (term->grid->view == term->grid->offset)
                 grid_render_scroll(term, buf, &it->item);
-                break;
+            break;
 
-            case DAMAGE_SCROLL_REVERSE:
+        case DAMAGE_SCROLL_REVERSE:
+            if (term->grid->view == term->grid->offset)
                 grid_render_scroll_reverse(term, buf, &it->item);
-                break;
-            }
+            break;
 
-            tll_remove(term->grid->scroll_damage, it);
+        case DAMAGE_SCROLL_IN_VIEW:
+            grid_render_scroll(term, buf, &it->item);
+            break;
+
+        case DAMAGE_SCROLL_REVERSE_IN_VIEW:
+            grid_render_scroll_reverse(term, buf, &it->item);
+            break;
         }
-    } else
-        tll_free(term->grid->scroll_damage);
+
+        tll_remove(term->grid->scroll_damage, it);
+    }
 
     if (term->render.workers.count > 0) {
 
diff --git a/terminal.h b/terminal.h
index 6f6e1d53..2a014d90 100644
--- a/terminal.h
+++ b/terminal.h
@@ -129,7 +129,9 @@ struct coord {
     int row;
 };
 
-enum damage_type {DAMAGE_SCROLL, DAMAGE_SCROLL_REVERSE};
+enum damage_type {DAMAGE_SCROLL, DAMAGE_SCROLL_REVERSE,
+                  DAMAGE_SCROLL_IN_VIEW, DAMAGE_SCROLL_REVERSE_IN_VIEW};
+
 struct damage {
     enum damage_type type;
     /* DAMAGE_SCROLL, DAMAGE_SCROLL_REVERSE */