How to enable GPU processing for preview playback?

My preview is incredibly slow/choppy from various edits/filters that I’ve put over my footage. I’ve seen that there’s a way to have the GPU handle doing the preview so that the playback is smoother, but I can’t seem to figure out how to turn that feature on.

The GPU is not used when previewing. Dan would like to do it, but it isn’t easy and so would take some effort to do. See here:

To get smoother previewing (but slower) you could switch off the setting:
Realtime (frame dropping)

That is not exactly correct. OpenGL is always used to display the video, and it often does a final step of colorspace conversion and scaling to fit the window. If Display Method = DirectX, then OpenGL is converted to DirectX. Here the GPU is used for preview but not for the image processing in filters, transitions, and track blending. You can turn on that unstable feature in the configuration file. However, it will not accelerate existing projects made using the CPU effects. I will not tell you further how to find the config file and turn it on because it is unsupported and this is for advanced users willing to make tests to see if it works OK for them. An advanced user will know how to locate the configuration document on the web site. Do not report bugs while this option is enabled.