Greg, I do this all the time, in fact, we built a custom 40 inch diagonal prompter head to play powerpoints on, that’s big enough to put two studio cameras behind it, one on a wider version of the shot, one tighter, so not only do we have perfect eye contact with the audience the whole time, I can live switch between the two cameras to keep things more interesting and punctuate ideas better. Getting a beamsplitter mirror for that size is tough and expensive: we wound up getting a mylar film to make the glass half-reflective, but even with naked glass, if we crank the maximum brightness from the LED tv set built in to this unit, it works.
So, to feed your laptop to a prompter you might be able to use HDM , SDI, or VGA, depends on the prompter’s monitor section… or you might have to first run a cable out of the laptop into a scan converter, then the scan converter feeds the prompter head. The “gotcha” that can come up is, at some point the video needs to be reversed and inverted, so that after it hits the mirror it reads correctly. Some prompting software does this automatically, but if you’re playing VGA graphics out of a laptop using powerpoint, you will need to flip the video stream coming out of the laptop. There’s a specific scan converter made just for this job, I will post the info on that tomorrow if I remember. That’s how we do it.
In a pinch, while saving up for said scan converter, you can cheat by taking all the PPT slides into photoshop or similar and pre-reversing them. You’re trading time for money here: save three hundred or so bucks by not buying the scan converter, but if you need to change a slide or add one on a moment’s notice, you can’t do it on the fly; you’d have to first pre-process it in photoshop. Or export the stills from PPT as jpegs, then re-import them and use powerpoint’s editing functions to flip them.
You have a good idea; pursue it! We did!