From d0c5cf6e9fa3c7f85531cfc3d3166c2cf7b6707e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Mon, 5 Oct 2020 18:33:50 +0200
Subject: [PATCH] =?UTF-8?q?sixel:=20reflow:=20drop=20sixels=20that=20cross?=
 =?UTF-8?q?es=20the=20scrollback=20history=E2=80=99s=20end?=
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This fixes various crashes that occurred after a reflow due to the
sixel image list invariants no longer being true.
---
 sixel.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/sixel.c b/sixel.c
index 0b971a90..898b8713 100644
--- a/sixel.c
+++ b/sixel.c
@@ -643,6 +643,29 @@ sixel_reflow(struct terminal *term)
                 continue;
             }
 
+            /* Drop sixels that now cross the current scrollback end
+             * border. This is similar to a sixel that have been
+             * scrolled out */
+            /* TODO: should be possible to optimize this */
+            bool sixel_destroyed = false;
+            int last_row = -1;
+
+            for (int j = 0; j < six->rows; j++) {
+                int row_no = rebase_row(term, six->pos.row + j);
+                if (last_row != -1 && last_row >= row_no) {
+                    sixel_destroy(six);
+                    sixel_destroyed = true;
+                    break;
+                }
+
+                last_row = row_no;
+            }
+
+            if (sixel_destroyed) {
+                LOG_WARN("destroyed sixel that now crossed history");
+                continue;
+            }
+
             /* Sixels that didn’t overlap may now do so, which isn’t
              * allowed of course */
             _sixel_overwrite_by_rectangle(