Manual DS4 mode: Allow Back/Select to trigger Touchpad click

[ekchang]

Description

When forcing manual DS4 emulation, there isn't a natural way to trigger Touchpad click for standard XInput. Current impl supports passing MISC_BUTTON (Xbox Series X Share button), but Steam Input doesn't expose this mapping, and most other XInput controllers on client don't have this button available.

Allow additional accessibility for clients wishing to emulate DS4 by having Back/Select also trigger Touchpad click. In most games supporting native DS4 input, Back/Share does not do anything anyway and typically should translate to a Touchpad click.

My specific usecase here is using Sunshine via Steam Deck Moonlight client. A DualShock 4 or DualSense controller configured via Steam Input cannot map the Touchpad click to Xbox 'Share' and the only way to pass through Touchpad clicks through to Sunshine is by disabling Steam Input altogether.

Screenshot

Issues Fixed or Closed

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• Bug fix (non-breaking change which fixes an issue)
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[CLAassistant]

All committers have signed the CLA.

[ReenigneArcher]

Thank you for the PR!

In addition to the below comments. I would also request the docs are updated. All config options are in the "advanced usage" section.

Also, perhaps this option should be named "ds4_back_as_touchpad_click" or something along those lines?

[ekchang]

Updated docs: