fix: resolution-dependent RGB565 byte order + GUI crash on HID handshake failure

RGB565 byte order: Windows TRCC ImageTo565 uses big-endian only for 320x320,
little-endian for all other resolutions (240x240, 480x480, etc.). Our code
was hardcoded to big-endian, causing swapped R/B channels on non-320x320
SCSI devices like FROZEN WARFRAME. Fixes #17.

GUI crash: HID devices with failed handshake keep resolution (0,0). The GUI
propagated this into setFixedSize(0,0) and theme directory lookups, causing
a PyQt6 segfault ("Memory access error"). Now guards against (0,0) and shows
a status message instead. Fixes #1 (PantherX12max crash).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Lexonight1

doc/USBLCD_PROTOCOL.md

@@ -206,13 +206,18 @@ Triggered when shared memory byte[3] == 0x7F.
 
 ## Pixel Format
 
-RGB565 big-endian, 2 bytes per pixel:
+RGB565, 2 bytes per pixel. **Byte order is resolution-dependent** (from Windows TRCC `ImageTo565`):
+
+- **320×320** (`is320x320`): big-endian — byte[0]=RRRRRGGG, byte[1]=GGGBBBBB
+- **Other resolutions** (240×240, 480×480, etc.): little-endian — byte[0]=GGGBBBBB, byte[1]=RRRRRGGG
 
 ```python
 r5 = (r >> 3) & 0x1F   # 5 bits red
 g6 = (g >> 2) & 0x3F   # 6 bits green
 b5 = (b >> 3) & 0x1F   # 5 bits blue
-pixel = (r5 << 11) | (g6 << 5) | b5  # uint16, stored big-endian
+pixel = (r5 << 11) | (g6 << 5) | b5  # uint16
+# 320x320: struct.pack('>H', pixel)   — big-endian
+# other:   struct.pack('<H', pixel)   — little-endian
 ```
 
 Total frame size = width × height × 2 bytes.

src/trcc/core/controllers.py

@@ -41,8 +41,15 @@
 )
 
 
-def image_to_rgb565(img: Any) -> bytes:
-    """Convert PIL Image to RGB565 bytes (big-endian, masked)."""
+def image_to_rgb565(img: Any, byte_order: str = '>') -> bytes:
+    """Convert PIL Image to RGB565 bytes.
+
+    Windows TRCC ImageTo565: big-endian for 320x320, little-endian otherwise.
+
+    Args:
+        img: PIL Image.
+        byte_order: '>' for big-endian, '<' for little-endian.
+    """
     if img.mode != 'RGB':
         img = img.convert('RGB')
 
@@ -51,7 +58,7 @@ def image_to_rgb565(img: Any) -> bytes:
     g = (arr[:, :, 1] >> 2) & 0x3F
     b = (arr[:, :, 2] >> 3) & 0x1F
     rgb565 = (r << 11) | (g << 5) | b
-    return rgb565.astype('>u2').tobytes()
+    return rgb565.astype(f'{byte_order}u2').tobytes()
 
 
 def apply_rotation(image: Any, rotation: int) -> Any:
@@ -1095,8 +1102,16 @@ def _send_frame_to_lcd(self, image: Any):
             self._handle_error(f"LCD send error: {e}")
 
     def _image_to_rgb565(self, img: Any) -> bytes:
-        """Convert PIL Image to RGB565 bytes."""
-        return image_to_rgb565(img)
+        """Convert PIL Image to RGB565 bytes.
+
+        Byte order matches Windows TRCC ImageTo565:
+        big-endian for 320x320, little-endian for other resolutions.
+        """
+        byte_order = '>'
+        device = self.devices.get_selected()
+        if device and device.protocol == 'scsi' and device.resolution != (320, 320):
+            byte_order = '<'
+        return image_to_rgb565(img, byte_order)
 
     # =========================================================================
     # Callbacks from sub-controllers

src/trcc/core/models.py

@@ -289,6 +289,7 @@ def detect_devices(self) -> List[DeviceInfo]:
                     device_index=d.get('device_index', 0),
                     protocol=d.get('protocol', 'scsi'),
                     device_type=d.get('device_type', 1),
+                    implementation=d.get('implementation', 'generic'),
                 )
                 for d in raw_devices
             ]

src/trcc/device_implementations.py

@@ -73,11 +73,21 @@ def get_frame_delay(self) -> float:
         """Delay between frames (seconds)"""
         return 0.0
 
+    @property
+    def pixel_byte_order(self) -> str:
+        """RGB565 byte order: '>' big-endian or '<' little-endian.
+
+        Windows TRCC ImageTo565 uses big-endian only for 320x320 (is320x320)
+        and SPIMode=2 (FBL 51/53). All other resolutions use little-endian.
+        """
+        if (self.width, self.height) == (320, 320):
+            return '>'
+        return '<'
+
     def rgb_to_bytes(self, r: int, g: int, b: int) -> bytes:
-        """Convert RGB to device pixel format"""
-        # RGB565 big-endian (default)
+        """Convert RGB to device pixel format (RGB565)."""
         pixel = ((r & 0xF8) << 8) | ((g & 0xFC) << 3) | (b >> 3)
-        return struct.pack('>H', pixel)
+        return struct.pack(f'{self.pixel_byte_order}H', pixel)
 
     def detect_resolution(self, device_path: str, verbose: bool = False) -> bool:
         """

src/trcc/qt_components/qt_app_mvc.py

@@ -797,9 +797,13 @@ def _on_device_selected(self, device: DeviceInfo):
             device.device_index, device.vid, device.pid)
         self.uc_preview.set_status(f"Device: {device.path}")
 
-        # Update resolution if changed
-        if device.resolution != (self.controller.lcd_width, self.controller.lcd_height):
-            self._on_resolution_changed(*device.resolution)
+        # Update resolution if changed (skip (0,0) — HID handshake failed)
+        w, h = device.resolution
+        if (w, h) == (0, 0):
+            self.uc_preview.set_status("Handshake failed — replug device and restart")
+            return
+        if (w, h) != (self.controller.lcd_width, self.controller.lcd_height):
+            self._on_resolution_changed(w, h)
 
         # Restore per-device brightness and rotation
         cfg = get_device_config(self._active_device_key)