How do I raise funds before I have a patent?

There are 3 sources of financing for startups, equity, grants and debt. Depending on your country and development pathway, you may be eligible for R&D grants ... for example Singapore (currently visiting for Robotics Week) has a $75 M fund for Deep Technologies (https://www.techinasia.com/spring-singapore-56m-startup-investment/). USPTO rules are that any offer for sale starts a countdown and you have 1 year to file a patent. However, this does not cover trade-secrets or confidential so you can prepare investor memorandums in two stages, a general overview and NDA due diligence. Note that the guidelines on "reduce to practice" is not strictly a complete prototype but to the point where it can be envisaged to work so your computer simulations may qualify (especially if on the visuals/parallax corrections etc) but be warned that software only patents will come under scrutiny. Depending on what you want to protect, (eg patents for hardware, copyright for software, trade secrets for autostereoscopic latency) you can have a mix of tactics.