Punch Glitch

Punch glitch is a bug that is exclusively encountered on the PlayStation 3 Jak and Daxter Collection.

Technical

During the development of the PC port for Jak and Daxter: The Precursor Legacy, it was discovered that punch glitch was occurring.

The issue is the acos in logic-target.gc. In PCSX2/PS2 it can never quite return 0.0. But on PC it does, and it causes 0/0 instead of 0/very-small-number. This is used as the input to a slerp and it ends up setting the output quaternion to 0 0 0 0. Over the next 2 frames, this completely breaks the dir-targ and unknown-quaternion00 and the target/camera rotation matrix ends up being identity. This sudden change rotates jak's velocity so it is entirely in the global x direction.

My understanding is that this should only happen when the dir-targ aligns with jak's velocity exactly. It may only be catastrophic if the camera is also aligned so that pushing forward on the stick will move jak in this direction.

I don't think the location has anything to do with it. It's possible that it only happens on ground that's perfectly level but I don't know. Instead, I think it tends to happen in places where people are lined up well with the camera and punching in/out of the camera exactly.

- Water111

The following code was added to acos in trigonometry.gc to fix the problem:

(defun acos ((arg0 float))
  "Inverse cosine. Returns rotation units"
  (let ((result (- 16384.000000 (asin arg0))))
    (#when PC_PORT
      ;; to avoid punch glitch:
      ;; (note: it might be a better fix to change the global rounding mode,
      ;;  but it's not super clear to me that the mode picked by PCSX2 is
      ;;  more accurate than normal in all cases. So, we'll do this for now.)
      (when (= result 0.0)
        (set! result 0.00000000001)
        )
      )
    result
    )
  )