>So I figured out that I needed to compute the line integral from the eye to every point on the screen. I learned some calculus in college, so I said to myself "I should be able to do this." So I figured out the formula for it with some crazy complicated trigonometry. I implemented it, but it was 100 times too slow. Then I realized, "Oh wait, I can do this in the lightmap space”, because the lightmap is a discretization of geometry into bite-sized chunks. I did that with lightmaps, so it was real-time.

What is lightmap space?