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fix(virtdisplay): stop enabling Composite by default -- it segfaults recording

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9654452 enabled Xvfb's Composite extension on the theory that #93 (no video
under headless="virtual") was caused by disabling it. Measurement disproves it:

  composite off + record_video_dir -> valid .webm, 24 pure-white frames
  composite ON  + record_video_dir -> browser dies with SIGSEGV, no video
  composite ON  + no recording     -> fine

So compositing does not fix #93, and defaulting it on turns a blank recording
into a crash for anyone recording under a virtual display. The segfault
reproduces on the shipped 152.0.4-beta.28 too, so it is a pre-existing fault in
the screencast capture path rather than something this branch introduced -- but
that is exactly why it should not be reached by default.

Kept as an opt-in (CAMOUFOX_VIRTUAL_DISPLAY_COMPOSITE=1) for hosts with real
GL, where it may behave differently. The real-screen-size half of 9654452 is
unaffected and stays.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Jake Writer
2026-07-28 11:16:29 -06:00
parent bb994a8299
commit 75d09a3dad
1 changed files with 16 additions and 6 deletions
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pythonlib/camoufox/virtdisplay.py
+16 -6
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@@ -29,12 +29,22 @@ DISPLAYFD_READ_TIMEOUT_S = 10.0
DEFAULT_SCREEN = "1920x1080x24"
SCREEN_ENV_VAR = "CAMOUFOX_VIRTUAL_DISPLAY_SIZE"
# The Composite extension. Offscreen rendering -- which is what Playwright's
# video recording relies on -- needs it, so disabling it silently broke
# record_video_dir under headless="virtual" (#93). A real X server has it, so
# enabling it is also the more faithful default.
# The Composite extension, disabled by default (Xvfb's `-extension COMPOSITE`).
#
# Set CAMOUFOX_VIRTUAL_DISPLAY_COMPOSITE=0 to go back to disabling it.
# This was briefly enabled by default on the theory that #93 (no video under
# headless="virtual") was caused by disabling it. Measurement says otherwise:
#
# composite off, record_video_dir -> a valid .webm of 24 pure-white frames
# composite ON, record_video_dir -> browser dies with SIGSEGV, no video
# composite ON, no recording -> fine
#
# So compositing does not fix #93, and turning it on converts a blank recording
# into a crash whenever someone records under a virtual display. Reproduced on
# both this build and the shipped 152.0.4-beta.28, so the segfault is in the
# screencast capture path, not something this branch introduced.
#
# Left as an opt-in for hosts with real GL where it may behave differently:
# set CAMOUFOX_VIRTUAL_DISPLAY_COMPOSITE=1 to enable it.
COMPOSITE_ENV_VAR = "CAMOUFOX_VIRTUAL_DISPLAY_COMPOSITE"
@@ -65,7 +75,7 @@ class VirtualDisplay:
self.debug = debug
self.screen = screen or _resolve_screen()
if composite is None:
composite = os.environ.get(COMPOSITE_ENV_VAR, "1").strip() not in ("0", "false", "")
composite = os.environ.get(COMPOSITE_ENV_VAR, "0").strip() in ("1", "true")
self.composite = composite
self.proc: Optional[subprocess.Popen] = None
self._display: Optional[int] = None