prompt: You will be provided with a partial code base and an issue statement explaining a problem to resolve.
  <issue>
  Default to QT_QPA_PLATFORM=xcb on Linux/Wayland
  If we detect a linux box running on wayland, we should force Qt to use the xcb platform as the wayland backend doesn't work properly with moderngl.
  
  This maybe a good way to detect wayland:
  ```
  XDG_SESSION_TYPE=wayland
  ```
  
  Relevant discussions:
  - https://github.com/abey79/vsketch/issues/353
  - https://discord.com/channels/550302843777712148/696045774970028062/1072436292798926868
  
  </issue>
  <code>
  [start of vpype_viewer/qtviewer/__init__.py]
  1 from .viewer import *
  2
  [end of vpype_viewer/qtviewer/__init__.py]
  </code>
  
  I need you to solve this issue by generating a single patch file that I can apply directly to this repository using git apply. Please respond with a single patch file in the following format.
  <patch>
  diff --git a/file.py b/file.py
  --- a/file.py
  +++ b/file.py
  @@ -1,27 +1,35 @@
   def euclidean(a, b):
  -    while b:
  -        a, b = b, a % b
  -    return a
  +    if b == 0:
  +        return a
  +    return euclidean(b, a % b)
   
   
   def bresenham(x0, y0, x1, y1):
       points = []
       dx = abs(x1 - x0)
       dy = abs(y1 - y0)
  -    sx = 1 if x0 < x1 else -1
  -    sy = 1 if y0 < y1 else -1
  -    err = dx - dy
  +    x, y = x0, y0
  +    sx = -1 if x0 > x1 else 1
  +    sy = -1 if y0 > y1 else 1
   
  -    while True:
  -        points.append((x0, y0))
  -        if x0 == x1 and y0 == y1:
  -            break
  -        e2 = 2 * err
  -        if e2 > -dy:
  -            err -= dy
  -            x0 += sx
  -        if e2 < dx:
  -            err += dx
  -            y0 += sy
  +    if dx > dy:
  +        err = dx / 2.0
  +        while x != x1:
  +            points.append((x, y))
  +            err -= dy
  +            if err < 0:
  +                y += sy
  +                err += dx
  +            x += sx
  +    else:
  +        err = dy / 2.0
  +        while y != y1:
  +            points.append((x, y))
  +            err -= dx
  +            if err < 0:
  +                x += sx
  +                err += dy
  +            y += sy
  +
  +    points.append((x, y))
       return points
  
  </patch>
golden_diff: diff --git a/vpype_viewer/qtviewer/__init__.py b/vpype_viewer/qtviewer/__init__.py
  --- a/vpype_viewer/qtviewer/__init__.py
  +++ b/vpype_viewer/qtviewer/__init__.py
  @@ -1 +1,18 @@
  +def _check_wayland():
  +    """Fix QT env variable on Wayland-based systems.
  +
  +    See https://github.com/abey79/vpype/issues/596
  +    """
  +    import os
  +    import sys
  +
  +    if sys.platform.startswith("linux"):
  +        if os.environ.get("XDG_SESSION_TYPE", "") == "wayland":
  +            if "QT_QPA_PLATFORM" not in os.environ:
  +                os.environ["QT_QPA_PLATFORM"] = "xcb"
  +
  +
  +_check_wayland()
  +
  +
   from .viewer import *
  
verification_info: {"golden_diff": "diff --git a/vpype_viewer/qtviewer/__init__.py b/vpype_viewer/qtviewer/__init__.py\n--- a/vpype_viewer/qtviewer/__init__.py\n+++ b/vpype_viewer/qtviewer/__init__.py\n@@ -1 +1,18 @@\n+def _check_wayland():\n+    \"\"\"Fix QT env variable on Wayland-based systems.\n+\n+    See https://github.com/abey79/vpype/issues/596\n+    \"\"\"\n+    import os\n+    import sys\n+\n+    if sys.platform.startswith(\"linux\"):\n+        if os.environ.get(\"XDG_SESSION_TYPE\", \"\") == \"wayland\":\n+            if \"QT_QPA_PLATFORM\" not in os.environ:\n+                os.environ[\"QT_QPA_PLATFORM\"] = \"xcb\"\n+\n+\n+_check_wayland()\n+\n+\n from .viewer import *\n", "issue": "Default to QT_QPA_PLATFORM=xcb on Linux/Wayland\nIf we detect a linux box running on wayland, we should force Qt to use the xcb platform as the wayland backend doesn't work properly with moderngl.\r\n\r\nThis maybe a good way to detect wayland:\r\n```\r\nXDG_SESSION_TYPE=wayland\r\n```\r\n\r\nRelevant discussions:\r\n- https://github.com/abey79/vsketch/issues/353\r\n- https://discord.com/channels/550302843777712148/696045774970028062/1072436292798926868\n", "before_files": [{"content": "from .viewer import *\n", "path": "vpype_viewer/qtviewer/__init__.py"}]}