feat: Optimize .t42 loading and improve decoder fidelity

.gitea/workflows/build-windows.yaml

@@ -10,8 +10,9 @@ jobs:
     steps:
       - name: Install Node.js
         run: |
+          apt-get clean
           apt-get update
-          apt-get install -y nodejs npm
+          apt-get install -y --fix-missing nodejs npm
 
       - name: Checkout
         uses: actions/checkout@v3
@@ -23,7 +24,7 @@ jobs:
 
       - name: Build Executable
         run: |
-          wine pyinstaller --onefile --windowed --name TeletextEditor_Windows.exe --paths src --add-data "app_icon.png;." --icon=app_icon.ico src/main.py
+          wine pyinstaller --onefile --windowed --hidden-import=pkgutil --hidden-import=PyQt6.sip --collect-all PyQt6 --name TeletextEditor_Windows.exe --paths src --add-data "app_icon.png;." --icon=app_icon.ico src/main.py
 
       - name: Upload Artifact
         uses: actions/upload-artifact@v3

build_app.py

@@ -27,6 +27,9 @@ def build():
         sys.executable, "-m", "PyInstaller",
         "--onefile",
         "--windowed",
+        "--hidden-import=pkgutil",
+        "--hidden-import=PyQt6.sip",
+        "--collect-all", "PyQt6",
         "--paths", "src",
         f"--add-data=app_icon.png{sep}.",
         "src/main.py"

src/main.py

@@ -23,10 +23,10 @@ def main():
         myappid = 'ddybing.teletexteditor.1.0' # arbitrary string
         ctypes.windll.shell32.SetCurrentProcessExplicitAppUserModelID(myappid)
 
+    QApplication.setDesktopFileName("no.ddybing.TeletextEditor") # Helps Linux DEs group windows
     app = QApplication(sys.argv)
     app.setApplicationName("TeletextEditor")
     app.setOrganizationName("DanielDybing")
-    app.setDesktopFileName("no.ddybing.TeletextEditor") # Helps Linux DEs group windows
     
     # Debug Image Formats
     supported_formats = [str(fmt, 'utf-8') for fmt in QImageReader.supportedImageFormats()]

src/teletext/io.py

@@ -5,69 +5,82 @@ from .models import Packet, Page, TeletextService
 def load_t42(file_path: str, progress_callback: Optional[Callable[[int, int], None]] = None) -> TeletextService:
     service = TeletextService()
     
+    if not os.path.exists(file_path):
+        return service
+        
     total_bytes = os.path.getsize(file_path)
-    # Each packet is 42 bytes
     total_packets = total_bytes // 42
     processed_packets = 0
     
+    # Magazine buffers: magazine -> {row_num: Packet}
+    magazine_buffers = {m: {} for m in range(1, 9)}
+    # Active page lookup: magazine -> Page object (for O(1) access)
+    active_pages = {m: None for m in range(1, 9)}
+    
     with open(file_path, 'rb') as f:
         while True:
             chunk = f.read(42)
-            if not chunk:
+            if not chunk: break
-                break
+            if len(chunk) < 42: break
-            if len(chunk) < 42:
-                # Should not happen in a valid T42 stream, or we just ignore incomplete tail
-                break
             
             processed_packets += 1
-            if progress_callback and processed_packets % 100 == 0:
+            if progress_callback and processed_packets % 500 == 0:
                 progress_callback(processed_packets, total_packets)
                 
             packet = Packet(chunk)
             service.all_packets.append(packet)
             
-            # Logic to group into pages.
+            mag = packet.magazine
-            # This is non-trivial because packets for a page might be interleaved or sequential.
+            buffer = magazine_buffers[mag]
-            # Standard implementation: Packets arrive in order. Row 0 starts a new page/subpage.
             
             if packet.row == 0:
-                # Start of a new page header.
+                p_num, sub_code, control_bits, language = parse_header(packet.data)
-                # Byte 2-9 of header contain Page Number, Subcode, Control bits etc.
-                # We need to parse the header to identify the page.
                 
-                # Header format (after Mag/Row):
+                # Check Erase Page bit (C4 is bit 0 of control_bits)
-                # Bytes: P1 P2 S1 S2 S3 S4 C1 C2 ...
+                erase_page = bool(control_bits & 1)
-                # All Hamming 8/4 encoded.
                 
-                # For now, let's just create a new page entry for every Header we see,
+                if erase_page:
-                # or find the existing one if we want to support updates (but T42 usually is a stream capture).
+                    magazine_buffers[mag] = {0: packet}
-                # If it's an editor file, it's likely sequential.
+                    buffer = magazine_buffers[mag]
-                
-                p_num, sub_code, language = parse_header(packet.data)
-                
-                # Create new page
-                new_page = Page(magazine=packet.magazine, page_number=p_num, sub_code=sub_code, language=language)
-                new_page.packets.append(packet)
-                service.pages.append(new_page)
-            else:
-                # Add to the "current" page of this magazine.
-                # We need to track the current active page for each magazine.
-                # A simplistic approach: add to the last page added that matches the magazine ??
-                # Robust approach: Maintain a dict of current_pages_by_magazine.
-                
-                # Let's find the last page in service that matches the packet's magazine
-                # This is O(N) but N (pages) is small.
-                target_page = None
-                for p in reversed(service.pages):
-                    if p.magazine == packet.magazine:
-                        target_page = p
-                        break
-                
-                if target_page:
-                    target_page.packets.append(packet)
                 else:
-                    # Packet without a header? Orphaned. Just keep in all_packets
+                    buffer[0] = packet
-                    pass
+                
+                # Create snapshot
+                new_page = Page(
+                    magazine=mag, 
+                    page_number=p_num, 
+                    sub_code=sub_code, 
+                    control_bits=control_bits,
+                    language=language
+                )
+                
+                # Efficient cloning: use the existing Packet objects where possible, 
+                # but we MUST clone the data bytearray if we plan to edit it later.
+                for r_num, pkt in sorted(buffer.items()):
+                    # Create a new packet shell sharing the original_data but with its own data bytearray
+                    cloned_pkt = Packet(pkt.original_data)
+                    cloned_pkt.data = bytearray(pkt.data)
+                    new_page.packets.append(cloned_pkt)
+                
+                service.pages.append(new_page)
+                active_pages[mag] = new_page # Update active page lookup
+                
+            elif 1 <= packet.row <= 31:
+                # Update the running buffer
+                buffer[packet.row] = packet
+                
+                # Update the active snapshot immediately
+                target_page = active_pages[mag]
+                if target_page:
+                    # Update row in the current active page
+                    found_row = False
+                    for i, p in enumerate(target_page.packets):
+                        if p.row == packet.row:
+                            target_page.packets[i] = packet
+                            found_row = True
+                            break
+                    if not found_row:
+                        target_page.packets.append(packet)
 
     return service
 
@@ -182,49 +195,110 @@ def decode_hamming_8_4(byte_val):
            (((byte_val >> 7) & 1) << 3)
 
 def parse_header(data: bytearray):
-    # Data is 40 bytes.
+    # Data is 40 bytes (after MRAG).
-    # Bytes 0-7 are Page Num (2), Subcode (4), Control (2) - ALL Hamming encoded.
+    # Byte 0: Page Units (PU)
-    
+    # Byte 1: Page Tens (PT)
-    # 0: Page Units (PU)
+    # Byte 2: Subcode S1 (bits 0-3)
-    # 1: Page Tens (PT)
+    # Byte 3: Subcode S2 (bits 4-6), C4 (bit 7)
+    # Byte 4: Subcode S3 (bits 8-11)
+    # Byte 5: Subcode S4 (bits 12-13), C5 (bit 14), C6 (bit 15)
+    # Byte 6: C7-C10
+    # Byte 7: C11-C14 (C12-C14 are Language)
     
     pu = decode_hamming_8_4(data[0])
     pt = decode_hamming_8_4(data[1])
     
-    # Use BCD/Hex-like storage: High nibble is Tens, Low nibble is Units.
+    # Page number: pt (tens), pu (units). 0x00 to 0xFF.
-    # This preserves Hex pages (A-F) without colliding with decimal pages.
-    # E.g. Page 1FF -> Tens=F(15), Units=F(15) -> 0xFF (255)
-    # Page 12E -> Tens=2, Units=E(14) -> 0x2E (46)
-    # Page 134 -> Tens=3, Units=4 -> 0x34 (52)
-    # 0x2E != 0x34. No collision.
     page_num = ((pt & 0xF) << 4) | (pu & 0xF)
     
-    # Subcode: S1, S2, S3, S4
+    # Subcode (13 bits)
-    # S1 (low), S2, S3, S4 (high)
-    
     s1 = decode_hamming_8_4(data[2])
     s2 = decode_hamming_8_4(data[3])
     s3 = decode_hamming_8_4(data[4])
     s4 = decode_hamming_8_4(data[5])
     
-    # Subcode logic is a bit complex with specific bit mapping for "Time" vs "Subcode"
+    sub_code = (s1 & 0xF) | \
-    # But usually just combining them gives the raw subcode value.
+              ((s2 & 0x7) << 4) | \
-    # S1: bits 0-3
+              ((s3 & 0xF) << 7) | \
-    # S2: bits 4-6 (bit 4 is C4) -> actually S2 has 3 bits of subcode + 1 control bit usually?
+              ((s4 & 0x3) << 11)
-    # Let's simplify and just concat them for a unique identifier.
               
-    sub_code = s1 | (s2 << 4) | (s3 << 8) | (s4 << 12)
+    # Control bits C4-C14
+    c4 = (s2 >> 3) & 1
+    c5 = (s4 >> 2) & 1
+    c6 = (s4 >> 3) & 1
     
-    # Control bits C12, C13, C14 are in Byte 8 (index 8)
+    c_7_10 = decode_hamming_8_4(data[6])
-    # They determine the National Option (Language)
+    c_11_14 = decode_hamming_8_4(data[7])
-    c_bits_2 = decode_hamming_8_4(data[8])
     
-    # Fix for Language Detection:
+    # bitmask starting at index 0 for C4
-    # It seems C12 and C13 are swapped in the Hamming decoding or file format relative to expected values.
+    control_bits = c4 | (c5 << 1) | (c6 << 2) | \
-    # C12 is bit 0, C13 is bit 1.
+                   ((c_7_10 & 0xF) << 3) | \
-    # We swap them so D1 maps to C13 (Swedish bit) and D2 maps to C12 (German bit).
+                   ((c_11_14 & 0xF) << 7)
-    # Original: language = c_bits_2 & 0b111
                    
-    language = ((c_bits_2 & 1) << 1) | ((c_bits_2 & 2) >> 1) | (c_bits_2 & 4)
+    # Language (C12, C13, C14)
+    # c_11_14: bit 0:C11, bit 1:C12, bit 2:C13, bit 3:C14
+    language = (c_11_14 >> 1) & 0x7
     
-    return page_num, sub_code, language
+    return page_num, sub_code, control_bits, language
+
+def save_tti(file_path: str, page: Page):
+    """
+    Saves a single Page object to a TTI file.
+    """
+    with open(file_path, 'w', encoding='latin-1') as f:
+        # Header Info
+        # DS - Source? Description?
+        f.write(f"DS,Teletext Editor Export\n")
+        f.write(f"SP,{file_path}\n")
+        
+        # PN - Page Number mpp00
+        # Typically TTI uses decimal integer for mppss? 
+        # Or mppss as hex digits? 
+        # Standard convention: mppss where m is 1-8, pp is 00-FF, ss is 00-99
+        # Example: Page 100 -> PN,10000
+        # Example: Page 1F0 -> PN,1F000
+        f.write(f"PN,{page.magazine}{page.page_number:02X}00\n")
+        
+        # SC - Subcode ssss
+        f.write(f"SC,{page.sub_code:04X}\n")
+        
+        # PS - Page Status
+        # 8000 is typical for "Transmission"
+        f.write(f"PS,8000\n")
+        
+        # RE - Region (Language)
+        f.write(f"RE,{page.language}\n")
+        
+        # Lines
+        # We need to construct the 40-char string for each row
+        # Row 0 is special (Header)
+        
+        # Get all packets for this page
+        # Map row -> packet
+        rows = {}
+        for p in page.packets:
+            rows[p.row] = p
+            
+        for r in range(26): # 0 to 25
+            if r in rows:
+                packet = rows[r]
+                # Packet data is 40 bytes (after the 2-byte header we stripped in Packet class? No wait)
+                # Packet.data in our model IS the 40 bytes of character data (we strip MRAG in __post_init__)
+                # So we just decode it as latin-1 to get the chars
+                
+                # However, we must ensure we don't have newlines or nulls breaking the text file structure
+                # TTI format usually accepts raw bytes 0x00-0xFF if strictly handled, but often expects
+                # mapped control codes.
+                # Standard VBIT2 TTI handling treats it as a binary-safe string if mapped to char.
+                
+                # Row 0 special handling: The first 8 bytes of Row 0 are usually header flags in the packet,
+                # but visually they are "P100    ".
+                # TTI usually expects the visual representation for the line content.
+                # But for transmission, we want the raw bytes.
+                # OL,r,String
+                
+                data_str = packet.data.decode('latin-1')
+                f.write(f"OL,{r},{data_str}\n")
+            else:
+                # Empty line? Usually omitted or written as empty
+                pass

src/teletext/models.py

@@ -1,6 +1,13 @@
 from dataclasses import dataclass, field
 from typing import List, Optional
 
+def decode_hamming_8_4(byte_val):
+    # Extract data bits: bits 1, 3, 5, 7
+    return ((byte_val >> 1) & 1) | \
+           (((byte_val >> 3) & 1) << 1) | \
+           (((byte_val >> 5) & 1) << 2) | \
+           (((byte_val >> 7) & 1) << 3)
+
 @dataclass
 class Packet:
     """
@@ -27,22 +34,6 @@ class Packet:
         b2 = self.original_data[1]
         
         # De-interleave Hamming bits to get M (3 bits) and R (5 bits)
-        # This is the "basic" interpretation. 
-        # For a robust editor we assume the input T42 is valid or we just store bytes.
-        # But we need Mag/Row to organize pages.
-        
-        # Decode Hamming 8/4 logic is complex to implementation from scratch correctly 
-        # without a reference, but usually D1, D2, D3, D4 are at bit positions 1, 3, 5, 7 
-        # (0-indexed, where 0 is LSB). 
-        # Let's perform a simple extraction assuming no bit errors for now.
-        
-        def decode_hamming_8_4(byte_val):
-            # Extract data bits: bits 1, 3, 5, 7
-            return ((byte_val >> 1) & 1) | \
-                   (((byte_val >> 3) & 1) << 1) | \
-                   (((byte_val >> 5) & 1) << 2) | \
-                   (((byte_val >> 7) & 1) << 3)
-
         d1 = decode_hamming_8_4(b1)
         d2 = decode_hamming_8_4(b2)
         
@@ -74,9 +65,13 @@ class Page:
     Can have multiple subpages.
     """
     magazine: int
-    page_number: int  # 00-99
+    page_number: int  # 00-99 (Hex storage: 0x00-0xFF)
-    sub_code: int = 0 # Subpage code (0000 to 3F7F hex usually, simplest is 0-99 equivalent)
+    sub_code: int = 0 # 13-bit subcode (0000 to 3F7F hex)
-    language: int = 0 # National Option (0-7)
+    
+    # Control bits C4-C14
+    control_bits: int = 0 
+    
+    language: int = 0 # National Option (0-7, from C12-C14)
     packets: List[Packet] = field(default_factory=list)
     
     @property
@@ -84,6 +79,112 @@ class Page:
         # Format as Hex to support A-F pages
         return f"{self.magazine}{self.page_number:02X}"
 
+    def get_control_bit(self, n: int) -> bool:
+        """ Returns value of control bit Cn (4-14) """
+        if 4 <= n <= 14:
+            return bool((self.control_bits >> (n - 4)) & 1)
+        return False
+
+    def set_control_bit(self, n: int, value: bool):
+        """ Sets value of control bit Cn (4-14) """
+        if 4 <= n <= 14:
+            if value:
+                self.control_bits |= (1 << (n - 4))
+            else:
+                self.control_bits &= ~(1 << (n - 4))
+
+    def calculate_crc(self) -> int:
+        """
+        Calculates the CRC-16 checksum for the page.
+        According to ETSI EN 300 706 (Section 9.6.1 & Figure 13):
+        - G(x) = x^16 + x^12 + x^9 + x^7 + 1 (Poly 0x1281)
+        - Initial value: 0.
+        - Processed bits b8 to b1 (MSB first for stored bytes).
+        - Total 1024 bytes (32 packets * 32 bytes).
+        - Packet X/0: Bytes 14 to 37 (24 bytes) + 8 spaces.
+        - Packets X/1 to X/25: Bytes 14 to 45 (32 bytes).
+        - Packets X/26 to X/31: 32 spaces each.
+        """
+        crc = 0
+        poly = 0x1281
+        
+        # Helper to update CRC with a byte (MSB first)
+        def update_crc(c, val):
+            v = (val << 8) & 0xFFFF
+            for _ in range(8):
+                if (c ^ v) & 0x8000:
+                    c = (c << 1) ^ poly
+                else:
+                    c = c << 1
+                v <<= 1
+                c &= 0xFFFF
+            return c
+
+        # Organize packets by row
+        rows = {p.row: p for p in self.packets}
+            
+        for r in range(32): # Process 32 slots (0-31)
+            start, end = 0, 0
+            padding = 0
+            
+            if r == 0:
+                # Row 0: Bytes 14-37 (24 bytes)
+                start, end = 8, 32 # data[8..31]
+                padding = 8 
+            elif 1 <= r <= 25:
+                # Rows 1-25: Bytes 14-45 (32 bytes)
+                start, end = 8, 40 # data[8..39]
+                padding = 0
+            else:
+                # Rows 26-31: 32 spaces each
+                padding = 32
+                
+            # Process packet data if available
+            if r in rows and start < end:
+                p_data = rows[r].data
+                for i in range(start, end):
+                    byte_val = (p_data[i] & 0x7F) if i < len(p_data) else 0x20
+                    crc = update_crc(crc, byte_val)
+            elif start < end:
+                # Missing packet but slot exists
+                for _ in range(start, end):
+                    crc = update_crc(crc, 0x20)
+            
+            # Add padding for this slot
+            for _ in range(padding):
+                crc = update_crc(crc, 0x20)
+                    
+        return crc
+
+    def get_stored_crc(self) -> Optional[int]:
+        """
+        Attempts to retrieve the stored CRC from Packet 27/0 if present.
+        Returns None if not found.
+        """
+        # Look for Packet 27
+        for p in self.packets:
+            if p.row == 27:
+                # Check Designation Code (Byte 0)
+                try:
+                    if len(p.data) >= 40:
+                        b0 = p.data[0]
+                        # Decode Hamming 8/4
+                        designation = decode_hamming_8_4(b0)
+                        
+                        # Packets X/27/0 to X/27/3 exist, but only X/27/0 has the CRC.
+                        # We also check if b0 is raw 0 as a fallback for some captures.
+                        if designation == 0 or b0 == 0:
+                            # Packet 27/0
+                            # Checksum is in bytes 38 and 39 (TBytes 44 and 45).
+                            hi = p.data[38]
+                            lo = p.data[39]
+                            
+                            crc = (hi << 8) | lo
+                            return crc
+                except:
+                    pass
+        return None
+
 @dataclass
 class TeletextService:
     """

src/teletext/renderer.py

@@ -214,10 +214,18 @@ class TeletextCanvas(QWidget):
             painter.end()
             return
             
-        # Draw each packet
+        # Check Control Bits for "Inhibit Display" (C10)
-        # Initialize a grid of empty chars
+        # In our bitmask (from parse_header):
-        grid = [None] * 26 # 0-25
+        # C4:0, C5:1, C6:2, C7:3, C8:4, C9:5, C10:6, C11:7, C12:8, C13:9, C14:10
+        inhibit_display = bool((self.page.control_bits >> 6) & 1)
+        if inhibit_display:
+            painter.setPen(Qt.GlobalColor.gray)
+            painter.drawText(10, 20, f"Page {self.page.full_page_number} - INHIBIT DISPLAY (C10 set)")
+            painter.end()
+            return
 
+        # Organize each packet by row
+        grid = [None] * 26 # 0-25
         for p in self.page.packets:
             if 0 <= p.row <= 25:
                 grid[p.row] = p
@@ -243,6 +251,10 @@ class TeletextCanvas(QWidget):
         # Output mask for the next row
         next_occlusion_mask = [False] * 40
 
+        # Check for Suppress Header (C7)
+        # C7:3, so bit 3 of control_bits
+        suppress_header = bool((self.page.control_bits >> 3) & 1)
+        
         # Default State at start of row
         fg = COLORS[7] # White
         bg = COLORS[0] # Black
@@ -252,6 +264,9 @@ class TeletextCanvas(QWidget):
         held_char = 0x20 # Space
         double_height = False
         
+        last_visible_idx = -1
+        bg_segments = [(0, bg)] # Track BG changes: (index, color)
+        
         y = row * self.cell_h
         
         data = b''
@@ -263,35 +278,24 @@ class TeletextCanvas(QWidget):
         # Header string for Row 0 columns 0-7
         header_prefix = ""
         if row == 0 and self.page:
-            header_prefix = f"P{self.page.magazine}{self.page.page_number:02d}"
+            header_prefix = f"P{self.page.magazine}{self.page.page_number:02X}"
             # Pad to 8 chars
             header_prefix = header_prefix.ljust(8)
             
         for c in range(40):
             x = c * self.cell_w
-            
-            # If this cell is occluded by the row above, skip drawing and attribute processing?
-            # Spec says "The characters in the row below are ignored."
-            # Ideally we shouldn't even process attributes, but for simple renderer we just skip draw.
-            # However, if we skip attribute processing, state (fg/bg) won't update. 
-            # Teletext attributes are serial.
-            # BUT, if the row above covers it, the viewer sees the row above.
-            # Does the hidden content affect the *rest* of the row?
-            # Likely yes, attributes usually propagate. 
-            # But the spec says "ignored". Let's assume we skip *everything* for this cell visually,
-            # but maybe we should technically maintain state?
-            # For "Double Height" visual correctness, skipping drawing is the key.
-            # We will Process attributes (to keep state consistent) but Skip Drawing if occluded.
-            
-            # Wait, if we process attributes, we might set double_height=True for the NEXT row?
-            # If this cell is occluded, it shouldn't trigger DH for the next row.
-            
             is_occluded = occlusion_mask[c]
             
             # Decide byte value
-            if row == 0 and c < 8:
+            if row == 0:
-                # Use generated header prefix
+                if c < 8:
-                byte_val = ord(header_prefix[c])
+                    # Column 0-7: Header prefix
+                    byte_val = ord(header_prefix[c])
+                elif suppress_header and c < 32:
+                    # Column 8-31: Hide header if C7 set
+                    byte_val = 0x20
+                else:
+                    byte_val = data[c] if c < len(data) else 0x20
             else:
                 byte_val = data[c] if c < len(data) else 0x20
                 
@@ -311,12 +315,33 @@ class TeletextCanvas(QWidget):
                     graphics_mode = True
                 elif byte_val == 0x1C: # Black BG
                     bg = COLORS[0]
+                    bg_segments.append((c, bg))
                 elif byte_val == 0x1D: # New BG
                     bg = fg
+                    bg_segments.append((c, bg))
+                    
                 elif byte_val == 0x0C: # Normal Height
                     double_height = False
                 elif byte_val == 0x0D: # Double Height
                     double_height = True
+                    # Backfill Height if we are in leading controls
+                    if last_visible_idx == -1:
+                        # Update occlusion mask for 0..c-1
+                        for k in range(c):
+                            next_occlusion_mask[k] = True
+                            
+                        # Repaint 0..c-1 with DH
+                        if draw_bg:
+                            # Repaint each cell with its historical BG
+                            for k in range(c):
+                                # Resolve BG for k
+                                cell_bg = bg_segments[0][1]
+                                for idx, color in reversed(bg_segments):
+                                    if idx <= k:
+                                        cell_bg = color
+                                        break
+                                painter.fillRect(k * self.cell_w, y, self.cell_w, self.cell_h * 2, cell_bg)
+
                 elif byte_val == 0x19: # Contiguous Graphics
                     contiguous = True
                 elif byte_val == 0x1A: # Separated Graphics
@@ -326,6 +351,23 @@ class TeletextCanvas(QWidget):
                 elif byte_val == 0x1F: # Release Graphics
                     hold_graphics = False
             
+            # Update visibility tracker
+            # If it's a control code, it's "invisible" (space) UNLESS Held Graphics draws something
+            visible_content = False
+            if is_control:
+                if hold_graphics and graphics_mode:
+                    visible_content = True
+            else:
+                 # Treat Space (0x20) as "invisible" for backfill purposes
+                 # This allows backfilling height over leading spaces in banners
+                 if byte_val > 0x20:
+                     visible_content = True
+                 
+            if visible_content:
+                # If this is the first visible char, mark it
+                if last_visible_idx == -1:
+                    last_visible_idx = c
+
             # Record Double Height for next row
             if double_height and not is_occluded:
                 next_occlusion_mask[c] = True
@@ -398,8 +440,8 @@ class TeletextCanvas(QWidget):
             if draw_fg and self.cursor_visible and c == self.cursor_x and row == self.cursor_y:
                  painter.setCompositionMode(QPainter.CompositionMode.CompositionMode_Difference)
                  # Difference with white creates inversion
-                 # Note: Cursor follows double height? Probably just the active cell.
+                 h_cursor = self.cell_h * 2 if double_height else self.cell_h
-                 painter.fillRect(x, y, self.cell_w, self.cell_h, QColor(255, 255, 255))
+                 painter.fillRect(x, y, self.cell_w, h_cursor, QColor(255, 255, 255))
                  painter.setCompositionMode(QPainter.CompositionMode.CompositionMode_SourceOver)
         
         return next_occlusion_mask

src/teletext/ui.py

@@ -6,9 +6,9 @@ from PyQt6.QtWidgets import (
     QCheckBox, QDialog, QGridLayout
 )
 from PyQt6.QtGui import QAction, QKeyEvent, QPainter, QBrush, QColor
-from PyQt6.QtCore import Qt, QRect
+from PyQt6.QtCore import Qt, QRect, QTimer
 
-from .io import load_t42, save_t42
+from .io import load_t42, save_t42, save_tti, decode_hamming_8_4, encode_hamming_8_4
 from .renderer import TeletextCanvas, create_blank_packet
 import copy
 import sys
@@ -121,10 +121,14 @@ class MainWindow(QMainWindow):
         
         self.service = TeletextService()
         self.current_page: Page = None
+        self.current_file_path = None
         self.clipboard = [] # List of (row, data_bytes)
         self.undo_stack = []
         self.redo_stack = []
         self.is_modified = False
+        self.language_overrides = {} # Session-based viewer overrides: (mag, pnum) -> lang_idx
+        
+        self.language_names = ["English", "German", "Swedish/Finnish", "Italian", "French", "Portuguese/Spanish", "Turkish", "Romania"]
 
         # UI Components
         self.central_widget = QWidget()
@@ -183,13 +187,30 @@ class MainWindow(QMainWindow):
         
         center_layout.addLayout(top_bar)
         
-        # Color Shortcuts
+        # Middle Layout (Canvas + Right Sidebar)
-        color_layout = QHBoxLayout()
+        middle_layout = QHBoxLayout()
+        center_layout.addLayout(middle_layout, 1)
         
+        # Canvas
+        self.canvas = TeletextCanvas()
+        self.canvas.cursorChanged.connect(self.on_cursor_changed)
+        middle_layout.addWidget(self.canvas, 1) # Expand
+        
+        # Right Sidebar
+        right_sidebar = QWidget()
+        right_sidebar.setFixedWidth(160)
+        right_layout = QVBoxLayout(right_sidebar)
+        right_layout.setContentsMargins(5, 0, 0, 0)
+        middle_layout.addWidget(right_sidebar)
+
+        # Color Shortcuts
         # Graphics Mode Toggle
         self.chk_graphics = QCheckBox("Graphics")
         self.chk_graphics.setToolTip("If checked, inserts Graphics Color codes (e.g. Red Graphics 0x11) instead of Alpha (0x01)")
-        color_layout.addWidget(self.chk_graphics)
+        right_layout.addWidget(self.chk_graphics)
+
+        colors_grid = QGridLayout()
+        colors_grid.setSpacing(5)
         
         colors = [
             ("Black", 0x00, "#000000"),
@@ -202,9 +223,10 @@ class MainWindow(QMainWindow):
             ("White", 0x07, "#FFFFFF"),
         ]
         
+        row, col = 0, 0
         for name, code, hex_color in colors:
             btn = QPushButton(name)
-            btn.setFixedSize(60, 30) # Fixed size for uniformity
+            btn.setFixedSize(60, 30) 
             
             # Common style
             style = f"background-color: {hex_color}; font-weight: bold; border: 1px solid #555; border-radius: 3px;"
@@ -220,20 +242,25 @@ class MainWindow(QMainWindow):
             
             # Use separate method to handle graphics check
             btn.clicked.connect(lambda checked, c=code: self.insert_color(c))
-            color_layout.addWidget(btn)
+            colors_grid.addWidget(btn, row, col)
+            
+            col += 1
+            if col > 1:
+                col = 0
+                row += 1
+        
+        right_layout.addLayout(colors_grid)
             
         # Mosaics Button
         btn_mosaic = QPushButton("Mosaics...")
         btn_mosaic.clicked.connect(self.open_mosaic_dialog)
-        color_layout.addWidget(btn_mosaic)
+        right_layout.addWidget(btn_mosaic)
 
-        color_layout.addStretch()
+        right_layout.addSpacing(10)
-        center_layout.addLayout(color_layout)
 
         # Background Controls
-        bg_layout = QHBoxLayout()
         bg_label = QLabel("Background:")
-        bg_layout.addWidget(bg_label)
+        right_layout.addWidget(bg_label)
 
         # New Background (0x1D)
         btn_new_bg = QPushButton("New BG")
@@ -241,7 +268,7 @@ class MainWindow(QMainWindow):
         btn_new_bg.setStyleSheet("background-color: #CCCCCC; color: black; font-weight: bold; border: 1px solid #555; border-radius: 3px;")
         btn_new_bg.setToolTip("Sets the current foreground color as the new background color (0x1D)")
         btn_new_bg.clicked.connect(lambda: self.insert_char(0x1D))
-        bg_layout.addWidget(btn_new_bg)
+        right_layout.addWidget(btn_new_bg)
 
         # Black Background (0x1C)
         btn_black_bg = QPushButton("Black BG")
@@ -249,15 +276,13 @@ class MainWindow(QMainWindow):
         btn_black_bg.setStyleSheet("background-color: black; color: white; font-weight: bold; border: 1px solid #555; border-radius: 3px;")
         btn_black_bg.setToolTip("Resets the background color to Black (0x1C)")
         btn_black_bg.clicked.connect(lambda: self.insert_char(0x1C))
-        bg_layout.addWidget(btn_black_bg)
+        right_layout.addWidget(btn_black_bg)
         
-        bg_layout.addStretch()
+        right_layout.addSpacing(10)
-        center_layout.addLayout(bg_layout)
 
         # Graphics Control
-        gfx_ctrl_layout = QHBoxLayout()
         gfx_ctrl_label = QLabel("Graphics Control:")
-        gfx_ctrl_layout.addWidget(gfx_ctrl_label)
+        right_layout.addWidget(gfx_ctrl_label)
 
         # Hold Graphics (0x1E)
         btn_hold = QPushButton("Hold Gfx")
@@ -265,7 +290,7 @@ class MainWindow(QMainWindow):
         btn_hold.setStyleSheet("background-color: #CCCCCC; color: black; font-weight: bold; border: 1px solid #555; border-radius: 3px;")
         btn_hold.setToolTip("Hold Graphics (0x1E): Displays the last graphic char in place of subsequent control codes.")
         btn_hold.clicked.connect(lambda: self.insert_char(0x1E))
-        gfx_ctrl_layout.addWidget(btn_hold)
+        right_layout.addWidget(btn_hold)
 
         # Release Graphics (0x1F)
         btn_release = QPushButton("Release Gfx")
@@ -273,15 +298,39 @@ class MainWindow(QMainWindow):
         btn_release.setStyleSheet("background-color: #CCCCCC; color: black; font-weight: bold; border: 1px solid #555; border-radius: 3px;")
         btn_release.setToolTip("Release Graphics (0x1F): Ends the 'Hold Graphics' effect.")
         btn_release.clicked.connect(lambda: self.insert_char(0x1F))
-        gfx_ctrl_layout.addWidget(btn_release)
+        right_layout.addWidget(btn_release)
         
-        gfx_ctrl_layout.addStretch()
+        right_layout.addSpacing(10)
-        center_layout.addLayout(gfx_ctrl_layout)
 
-        # Canvas
+        # Page Language Setting
-        self.canvas = TeletextCanvas()
+        lang_group_label = QLabel("Page Language:")
-        self.canvas.cursorChanged.connect(self.on_cursor_changed)
+        right_layout.addWidget(lang_group_label)
-        center_layout.addWidget(self.canvas, 1) # Expand
+        
+        lang_layout = QHBoxLayout()
+        self.lang_combo = QComboBox()
+        self.lang_combo.addItems(self.language_names)
+        self.lang_combo.setToolTip("Select the National Option Character Set for this page.")
+        
+        btn_set_lang = QPushButton("Set")
+        btn_set_lang.setFixedWidth(40)
+        btn_set_lang.clicked.connect(self.apply_language_change)
+        btn_set_lang.setToolTip("Apply this language setting to the page header.")
+        
+        lang_layout.addWidget(self.lang_combo)
+        lang_layout.addWidget(btn_set_lang)
+        right_layout.addLayout(lang_layout)
+
+        right_layout.addSpacing(10)
+
+        # CRC Checksum
+        crc_label = QLabel("CRC Checksum:")
+        right_layout.addWidget(crc_label)
+        
+        self.lbl_crc_info = QLabel("Page: ----\nCalc: ----")
+        self.lbl_crc_info.setStyleSheet("font-family: monospace; font-weight: bold;")
+        right_layout.addWidget(self.lbl_crc_info)
+        
+        right_layout.addStretch()
         
         self.layout.addLayout(center_layout, 1)
         
@@ -304,15 +353,38 @@ class MainWindow(QMainWindow):
         self.language_label = QLabel("Lang: English")
         self.status_bar.addPermanentWidget(self.language_label)
 
-        self.language_names = ["English", "German", "Swedish/Finnish", "Italian", "French", "Portuguese/Spanish", "Turkish", "Romania"]
-
         # Menus
         self.create_menus()
 
+    def update_crc_display(self):
+        if not self.current_page:
+            self.lbl_crc_info.setText("Page: ----\nCalc: ----")
+            self.lbl_crc_info.setStyleSheet("font-family: monospace; font-weight: bold;")
+            return
+            
+        calc_crc = self.current_page.calculate_crc()
+        stored_crc = self.current_page.get_stored_crc()
+        
+        stored_str = f"{stored_crc:04X}" if stored_crc is not None else "----"
+        calc_str = f"{calc_crc:04X}"
+        
+        # Highlight if match
+        if stored_crc is not None:
+            if stored_crc == calc_crc:
+                style = "font-family: monospace; font-weight: bold; color: green;"
+            else:
+                style = "font-family: monospace; font-weight: bold; color: red;"
+        else:
+             style = "font-family: monospace; font-weight: bold;"
+             
+        self.lbl_crc_info.setStyleSheet(style)
+        self.lbl_crc_info.setText(f"Page: {stored_str}\nCalc: {calc_str}")
+
     def update_language_label(self):
         idx = self.canvas.subset_idx
         if 0 <= idx < len(self.language_names):
             self.language_label.setText(f"Lang: {self.language_names[idx]}")
+            self.lang_combo.setCurrentIndex(idx)
         else:
             self.language_label.setText(f"Lang: Unknown ({idx})")
 
@@ -371,6 +443,10 @@ class MainWindow(QMainWindow):
         save_as_action.triggered.connect(self.save_as_file)
         file_menu.addAction(save_as_action)
         
+        export_tti_action = QAction("Export to TTI...", self)
+        export_tti_action.triggered.connect(self.export_tti)
+        file_menu.addAction(export_tti_action)
+        
         close_action = QAction("Close File", self)
         close_action.triggered.connect(self.close_file)
         file_menu.addAction(close_action)
@@ -422,10 +498,71 @@ class MainWindow(QMainWindow):
         if action:
             idx = action.data()
             self.canvas.subset_idx = idx
+            
+            # Store session override for the current page (magazine + page number)
+            if self.current_page:
+                key = (self.current_page.magazine, self.current_page.page_number)
+                self.language_overrides[key] = idx
+                
             self.canvas.redraw()
             self.canvas.update()
             self.update_language_label()
 
+    def apply_language_change(self):
+        if not self.current_page:
+            return
+            
+        idx = self.lang_combo.currentIndex()
+        if idx < 0: return
+        
+        # Update the model
+        self.current_page.language = idx
+        
+        # Also update the session override/viewer to match
+        self.canvas.subset_idx = idx
+        key = (self.current_page.magazine, self.current_page.page_number)
+        self.language_overrides[key] = idx
+        
+        # Patch Row 0 packet data to persist language selection to file
+        # Language bits are in Byte 7 (Control Bits C11-C14)
+        # Byte 7 encoded structure: bit 0:C11, bit 1:C12, bit 2:C13, bit 3:C14
+        # National Option index corresponds to (C14 C13 C12)
+        
+        # Find Row 0 packet
+        header_packet = None
+        for p in self.current_page.packets:
+            if p.row == 0:
+                header_packet = p
+                break
+        
+        if header_packet and len(header_packet.data) >= 8:
+            try:
+                # Byte 7 contains C11, C12, C13, C14
+                old_val = decode_hamming_8_4(header_packet.data[7])
+                
+                l0 = (idx >> 0) & 1 # C12
+                l1 = (idx >> 1) & 1 # C13
+                l2 = (idx >> 2) & 1 # C14
+                
+                d1 = (old_val >> 0) & 1 # Preserve C11
+                d2 = l0
+                d3 = l1
+                d4 = l2
+                
+                new_val = d1 | (d2 << 1) | (d3 << 2) | (d4 << 3)
+                
+                header_packet.data[7] = encode_hamming_8_4(new_val)
+                self.set_modified(True)
+                self.status_label.setText(f"Language set to {self.language_names[idx]} (saved to header).")
+            except Exception as e:
+                self.status_label.setText(f"Error setting language: {e}")
+        else:
+            self.status_label.setText("No header packet found to update.")
+            
+        self.canvas.redraw()
+        self.canvas.update()
+        self.update_language_label()
+
     def prev_subpage(self):
         count = self.subpage_combo.count()
         if count <= 1: return
@@ -460,9 +597,10 @@ class MainWindow(QMainWindow):
         
         self.undo_stack.clear()
         self.redo_stack.clear()
+        self.language_overrides.clear()
         
-        QMessageBox.information(self, "Closed", "File closed.")
+        self.status_label.setText("File closed.")
-        self.status_label.setText("Ready")
+        QTimer.singleShot(3000, lambda: self.status_label.setText("Ready"))
         self.set_modified(False)
 
 
@@ -501,9 +639,9 @@ class MainWindow(QMainWindow):
 
     def save_file(self) -> bool:
         if not self.current_file_path:
-             fname, _ = QFileDialog.getSaveFileName(self, "Save T42", "", "Teletext Files (*.t42)")
+             # User requested status message instead of Save As behavior for empty state
-             if not fname: return False
+             self.status_label.setText("No file loaded to save. Please use 'Save As...' or 'Open' first.")
-             self.current_file_path = fname
+             return False
         
         try:
             self.progress_bar.setVisible(True)
@@ -529,6 +667,20 @@ class MainWindow(QMainWindow):
             self.status_label.setText("Error saving file")
             return False
 
+    def export_tti(self):
+        if not self.current_page:
+            QMessageBox.warning(self, "Export TTI", "No page selected to export.")
+            return
+            
+        fname, _ = QFileDialog.getSaveFileName(self, "Export to TTI", "", "Teletext Text Image (*.tti)")
+        if not fname: return
+        
+        try:
+            save_tti(fname, self.current_page)
+            QMessageBox.information(self, "Export Successful", f"Page exported to {os.path.basename(fname)}")
+        except Exception as e:
+            QMessageBox.critical(self, "Export Failed", f"Failed to export TTI: {e}")
+
     def copy_page_content(self):
         if not self.current_page:
             return
@@ -582,6 +734,7 @@ class MainWindow(QMainWindow):
         # Force redraw
         self.canvas.redraw()
         self.canvas.update()
+        self.update_crc_display()
         self.status_label.setText(f"Pasted {modified_count} rows.")
         self.push_undo_state() # Push state after paste? NO, before! 
         # Wait, usually we push before modifying.
@@ -685,6 +838,7 @@ class MainWindow(QMainWindow):
         self.canvas.set_page(self.current_page)
         self.canvas.redraw()
         self.canvas.update()
+        self.update_crc_display()
 
     def populate_list(self):
         self.page_list.clear()
@@ -718,9 +872,21 @@ class MainWindow(QMainWindow):
         self.subpage_combo.clear()
         
         for i, p in enumerate(pages):
-            # Display format: Index or Subcode?
+            # Try to find the clock in Row 0 (last 8 characters)
-            # Subcode is often 0000. Index 1/N is clearer for editing.
+            clock_str = ""
-            label = f"{i+1}/{len(pages)} (Sub {p.sub_code:04X})"
+            for pkt in p.packets:
+                if pkt.row == 0:
+                    # Bytes 32-39 of the 40-byte data are the clock
+                    raw_clock = pkt.data[32:40].decode('latin-1', errors='replace')
+                    # Strip parity from each char and filter non-printables
+                    clock_str = "".join([chr(ord(c) & 0x7F) if 32 <= (ord(c) & 0x7F) <= 126 else " " for c in raw_clock])
+                    break
+            
+            label = f"{i+1}/{len(pages)} "
+            if clock_str.strip():
+                label += f"[{clock_str.strip()}] "
+            label += f"(Sub {p.sub_code:04X})"
+            
             self.subpage_combo.addItem(label, p)
             
         self.subpage_combo.blockSignals(False)
@@ -736,7 +902,16 @@ class MainWindow(QMainWindow):
         if isinstance(page, Page):
             self.current_page = page
             self.canvas.set_page(page)
+            
+            # Apply session language override if it exists for this page
+            key = (page.magazine, page.page_number)
+            if key in self.language_overrides:
+                self.canvas.subset_idx = self.language_overrides[key]
+                self.canvas.redraw()
+                self.canvas.update()
+                
             self.update_language_label()
+            self.update_crc_display()
             self.canvas.setFocus()
 
     def insert_char(self, char_code):
@@ -761,6 +936,7 @@ class MainWindow(QMainWindow):
         self.hex_input.setText(f"{val:02X}")
         mode_str = "Graphics" if is_graphics else "Text"
         self.mode_label.setText(f"Mode: {mode_str}")
+        self.update_crc_display()
         
     def on_hex_entered(self):
         text = self.hex_input.text()