feat: Optimize .t42 loading and improve decoder fidelity

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
 
@@ -182,52 +195,51 @@ 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):
     """

src/teletext/models.py

@@ -65,9 +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
@@ -75,6 +79,20 @@ 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.

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
@@ -272,29 +284,18 @@ class TeletextCanvas(QWidget):
             
         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
                 

src/teletext/ui.py

@@ -524,8 +524,9 @@ class MainWindow(QMainWindow):
         self.language_overrides[key] = idx
         
         # Patch Row 0 packet data to persist language selection to file
-        # Language bits are in Byte 8 (Control Bits 2): C12, C13, C14
+        # Language bits are in Byte 7 (Control Bits C11-C14)
-        # We need to preserve C11 (bit 3 of encoded 4-bit val) which is "Inhibit Display" usually 0
+        # 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
@@ -534,36 +535,23 @@ class MainWindow(QMainWindow):
                 header_packet = p
                 break
         
-        if header_packet and len(header_packet.data) > 8:
+        if header_packet and len(header_packet.data) >= 8:
             try:
-                old_val = decode_hamming_8_4(header_packet.data[8])
+                # Byte 7 contains C11, C12, C13, C14
-                # Encoded nibble structure: D1(b0), D2(b1), D3(b2), D4(b3)
+                old_val = decode_hamming_8_4(header_packet.data[7])
-                # D1 maps to C12
-                # D2 maps to C13
-                # D3 maps to C14
-                # D4 maps to C11
                 
-                # io.py logic for reading:
+                l0 = (idx >> 0) & 1 # C12
-                # language = ((c_bits_2 & 1) << 1) | ((c_bits_2 & 2) >> 1) | (c_bits_2 & 4)
+                l1 = (idx >> 1) & 1 # C13
-                # i.e. Lang Bit 0 comes from D2, Lang Bit 1 comes from D1, Lang Bit 2 comes from D3
+                l2 = (idx >> 2) & 1 # C14
                 
-                # So for writing:
+                d1 = (old_val >> 0) & 1 # Preserve C11
-                # D1 = Lang Bit 1
-                # D2 = Lang Bit 0
-                # D3 = Lang Bit 2
-                
-                l0 = (idx >> 0) & 1
-                l1 = (idx >> 1) & 1
-                l2 = (idx >> 2) & 1
-                
-                d1 = l1
                 d2 = l0
-                d3 = l2
+                d3 = l1
-                d4 = (old_val >> 3) & 1 # Preserve C11
+                d4 = l2
                 
                 new_val = d1 | (d2 << 1) | (d3 << 2) | (d4 << 3)
                 
-                header_packet.data[8] = encode_hamming_8_4(new_val)
+                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:
@@ -884,9 +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)