Rectangle Light diffuse vs 3DS Max

Just a quick note on rectangle light diffuse. In XLE, rectangle lights are slightly different from the default rectangle lights in 3DS Max.

XLE lights	3DS Max lights (Quicksilver renderer)

XLE rectangle lights emit light mostly in the forward direction (and a reduced amount sideways). But in the 3DS Max Quicksilver renderer, rectangle lights emit light in all direction.

Edge cases

This is partially because the method we're using for diffuse doesn't work well on extreme angles. In the above example, the light plane and the top/bottom/left/right walls are actually perpendicular.

This causes weird problems right on the edges.

XLE emulating 3DS Max	3DS Max lights (Quicksilver Renderer)

In the above example, the left and right walls look fine. But the top and bottom walls are missing their highlight. This is because the light is quite tall. A square light might be fine.

But you can see that, in general, the 3DS Max result and the XLE result is quite similar.

Practical uses

It might be possible to fix this with some research and a few tricks. But it's not clear if that would really be useful. Rectangle lights might be most useful for things like windows, TV screens, photography reflectors, etc. In these cases we normally want the light to always go forward, anyway.

Plus, if we block off the extreme edges, we have some easy options for shadowing.