From 75e258280290f6b766261293d7237efc349fda6b Mon Sep 17 00:00:00 2001
From: Mathieu Duponchelle <mathieu@centricular.com>
Date: Fri, 4 Jul 2025 00:29:23 +0200
Subject: [PATCH] tttocea708/translate: improve logic for prepending spaces

No space needs to be prepended after inserting a carriage return or
clearing the screen.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/2345>
---
 .../closedcaption/src/tttocea708/translate.rs | 24 +++++++++++++++----
 video/closedcaption/tests/tttocea708.rs       |  6 ++---
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/video/closedcaption/src/tttocea708/translate.rs b/video/closedcaption/src/tttocea708/translate.rs
index cbafb1028..65d739fcb 100644
--- a/video/closedcaption/src/tttocea708/translate.rs
+++ b/video/closedcaption/src/tttocea708/translate.rs
@@ -391,6 +391,7 @@ impl TextToCea708 {
                 }
                 self.pen_location.column = origin_column as u8;
                 need_pen_location = true;
+                cleared = true;
             }
         }
 
@@ -437,12 +438,17 @@ impl TextToCea708 {
 
             for (i, chunk) in line.chunks.iter().enumerate() {
                 let (cr, mut prepend_space) = if i == 0 {
-                    (line.carriage_return, true)
+                    (
+                        line.carriage_return,
+                        line.carriage_return.map(|cr| !cr).unwrap_or(!cleared),
+                    )
                 } else {
                     (Some(false), false)
                 };
                 self.open_line(chunk, cr);
 
+                cleared = false;
+
                 if is_punctuation(&chunk.text) {
                     prepend_space = false;
                 }
@@ -463,9 +469,7 @@ impl TextToCea708 {
                         continue;
                     }
 
-                    let code = Code::from_char(c).unwrap_or(Code::Space);
-                    self.service_writer.push_codes(&[code]);
-                    self.pen_location.column += 1;
+                    let mut push_code = true;
 
                     if self.mode == Cea708Mode::RollUp {
                         /* In roll-up mode, we introduce carriage returns automatically.
@@ -488,8 +492,18 @@ impl TextToCea708 {
                             self.pen_location.column = self.origin_column as u8;
 
                             self.open_line(chunk, Some(true));
+
+                            push_code = !c.is_ascii_whitespace();
                         }
-                    } else if self.pen_location.column > 31 {
+                    }
+
+                    if push_code {
+                        let code = Code::from_char(c).unwrap_or(Code::Space);
+                        self.service_writer.push_codes(&[code]);
+                        self.pen_location.column += 1;
+                    }
+
+                    if self.mode != Cea708Mode::RollUp && self.pen_location.column > 31 {
                         if chars.peek().is_some() {
                             gst::warning!(CAT, "Dropping characters after 32nd column: {}", c);
                         }
diff --git a/video/closedcaption/tests/tttocea708.rs b/video/closedcaption/tests/tttocea708.rs
index 5a24223f7..ab98dd80e 100644
--- a/video/closedcaption/tests/tttocea708.rs
+++ b/video/closedcaption/tests/tttocea708.rs
@@ -56,7 +56,7 @@ static PADDING: [u8; 60] = [
 ];
 
 static POP_ON_PREAMBLE: [u8; 24] = [
-    0xff, 0x0d, 0x37, 0xfe, 0x88, 0x01, 0xfe, 0x8c, 0xfe, 0xfe, 0x99, 0x18, 0xfe, 0xe4, 0x32, 0xfe,
+    0xff, 0x0c, 0x36, 0xfe, 0x88, 0x01, 0xfe, 0x8c, 0xfe, 0xfe, 0x99, 0x18, 0xfe, 0xe4, 0x32, 0xfe,
     0x7e, 0x1f, 0xfe, 0x11, 0x92, 0xfe, 0x0e, 0x00,
 ];
 
@@ -81,8 +81,8 @@ fn test_tttocea708_one_timed_buffer_and_eos() {
     expected0[..3].copy_from_slice(&[0xfc, 0x94, 0x20]);
     expected0[6..30].copy_from_slice(&POP_ON_PREAMBLE);
     // Hello ETX
-    expected0[30..45].copy_from_slice(&[
-        0xfe, 0x20, 0x48, 0xfe, 0x65, 0x6c, 0xfe, 0x6c, 0x6f, 0xfe, 0x8b, 0x03, 0xfe, 0x03, 0x00,
+    expected0[30..42].copy_from_slice(&[
+        0xfe, 0x48, 0x65, 0xfe, 0x6c, 0x6c, 0xfe, 0x6f, 0x8b, 0xfe, 0x03, 0x03,
     ]);
     let mut expected1 = PADDING;
     expected1[..3].copy_from_slice(&[0xfc, 0x94, 0xae]);