Firstly, you will need adb for this method.
Because Android does not allow adb connection if the device was not unlocked, you can't access adb from the system itself in your situation. Instead, you will need some recovery that gives you adb access.
twrp (Team Win Recovery Project)'s recovery gives you adb access. What you want to do is install TWRP on the OnePlus One (bacon) device; you can download the img file from here.
Next, you want to make sure that you unlocked the bootloader. If you didn't beforehand then you're out of luck¹ – but if the device is unlocked, boot into fastboot (hold volume up + power until the "fastboot" screen appears). You then could install TWRP by typing this command:
option 1 (installing TWRP to the device):
fastboot flash recovery [TWRP.img on your computer]
or option 2 (just booting it once without installing):
fastboot boot [TWRP.img on your computer]
then reboot to recovery (only option 1 – option 2 does that automatically).
Now, to remove the pattern lock, run
adb shell rm /data/system/gesture.key, and reboot the device.
¹ If you havn't unlocked the device yet, unlocking it will wipe everything (including the pattern lock) so adb wont matter. If you do want to unlock the device (your own risk):
- reboot to bootloader
- type in
fastboot oem unlock.
that's it. hope it helped you.