Windows Management: Dealing with HDMI Matrix

[macdaddie]

Monitor name lost after HDMI matrix switch – workaround using UUID fallback in Hammerspoon

Context

I'm using a macOS setup with multiple external monitors, one of which is routed through an HDMI matrix switch. When I toggle the matrix to another source and then return it back to the Mac, Hammerspoon loses access to the monitor’s display name via hs.screen:name() — it returns nil or "".

The reason I'm using `name()' rather than the screen position is that following the use of the HDMI matrix the screens can reorder themselves randomly.

Despite trying things like:

• hs.reload()
• hs.screen.restoreGamma()
• killall -HUP WindowServer

…macOS doesn't re-register the display name for the HDMI-matrix-connected monitor. However, interestingly, the monitor's UUID (hs.screen:getUUID()) remains stable across switches.

This breaks any monitor-specific logic that relies on screen:name() (like placing windows on a named screen).

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Problem Summary

After switching an HDMI matrix away from and back to a Mac-connected monitor:

• screen:name() becomes nil or ""
• Hammerspoon can no longer detect the monitor by name
• UUIDs are still available and reliable
• hs.reload() or even WindowServer resets do not restore the name

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My Workaround

Since only one of my monitors is routed through the matrix, I wrote logic to assume that any screen with no name is the matrix-connected monitor, and fallback to using its UUID.

local screen = hs.screen.mainScreen()
local sname = screen:name()

if sname == "VE228" or sname == nil or sname == "" then
  top_right = screen:getUUID()
end

This allows me to:

• Keep using monitor-specific logic
• Avoid hard failures when name detection breaks
• Work around macOS not re-polling the EDID over HDMI via the matrix

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Caveat

This workaround is fine as long as you only have one matrix-routed monitor. It falls down if you have multiple monitors plugged into the HDMI matrix if they all lose their name.

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Would love input from others:

• Is there a way to force macOS or Hammerspoon to re-fetch EDID / display name metadata?
• Any best practices around using hs.screen with matrixed or virtual monitors?

Hopefully this helps someone else running into the same issue!