avfilter/vf_drawtext: fix newline rendered as .notdef glyph

quink-black · Zhao Zhili · commit fd9f1e9c52d4 · 2026-03-26T07:24:15.000Z
GET_UTF8 advances the pointer past the newline byte before the
newline check, so shape_text_hb receives text that includes the
newline character. Since HarfBuzz does not treat U+000A as
default-ignorable, it gets shaped into a .notdef glyph.

Fixes #21565

Reported-by: scriptituk &lt;info@scriptit.uk&gt;
Signed-off-by: Zhao Zhili &lt;zhilizhao@tencent.com&gt;
diff --git a/libavfilter/vf_drawtext.c b/libavfilter/vf_drawtext.c
@@ -1452,13 +1452,14 @@ static int measure_text(AVFilterContext *ctx, TextMetrics *metrics)
             s->tab_clusters[tab_idx++] = i;
             *p = ' ';
         }
+        size_t len = p - start;
         GET_UTF8(code, *p ? *p++ : 0, code = 0xfffd; goto continue_on_failed2;);
 continue_on_failed2:
         if (ff_is_newline(code) || code == 0) {
             TextLine *cur_line = &s->lines[line_count];
             HarfbuzzData *hb = &cur_line->hb_data;
             cur_line->cluster_offset = line_offset;
-            ret = shape_text_hb(s, hb, start, p - start);
+            ret = shape_text_hb(s, hb, start, len);
             if (ret != 0) {
                 goto done;
             }
