Directional Light Actor Position Affects Preview Shadows Indicator (preview watermark). Huh?

Hello Fellow Developers,

Assumption: The position of a stationary Directional Light Actor in a level makes no difference since it’s based on light coming from infinitely far away and only the direction of the light matters, which is performed by changing its Y and/or Z rotation since the light is always aligned with the X axis). Directional Lights | Unreal Engine Documentation

Question: Why is it that if I move the Directional Light Actor, the “Preview” shadow indicator (this is found in viewport > show > visualize > preview shadows indicator) moves?

This image shows the directional light selected and shows its Transform data. As you can see, the direction of the light is the White Arrow defined by the Actor’s Rotation. Focus on the Z position (100 units)

Without moving the position of the view into the world through the viewport, I move the directional light up 47 units, and this is the result. Notice the word “Preview” has moved.

It seems as though it’s on a cycle; where if I move a magic number of units, the pattern will repeat, as if the words “Preview” are going in a rotation (circle) of some sort.

The reason I’m confused is because I thought changing the Directional Light Actor position made no difference (in world space of course, if it had a rotation, then moving it along its local space would change the angle of the light). This is the way I understand it to be, and if this is indeed true, then why does the Preview Shadow data change with the location of the Directional Light Actor?

Yes, I understand the “Preview” is an indicator of sorts to visualize where shadows ‘would’ be because light was changed, but why does the indicator move? Is there something I don’t understand about directional light?


I would say that’s probably a flaw with the editor, since you’re right about the position not affecting the shadows, you can even see that the shadows haven’t changed. It’s probably something where it’s just checking if the transform of the light has changed then invalidate lighting.

The Preview Shadows Indicator is a tiling Light Function using standard UV coordinates, so it will offset based on the projecting light’s position. If it bothers you, you could change it to a world-space projection since the material is located in the Engine Content section.

Hi rosegoldslugs: It doesn’t bother me. The editor has this built in for a purpose and I find it useful. Could you point me where in the documentation I may find what you say in your first sentence? this? I’d like to learn more. Thank you!

There isn’t much on light functions specifically, but I know they’re covered in a few videos on YouTube as well. Here’s the official documentation though: Using Light Functions in Unreal Engine | Unreal Engine Documentation

And you can find it in the Content Browser if you make Engine Content visible(Get access to the Engine folder in content browser - AnswerHub - Unreal Engine Forums), then search for “Preview” while Engine Content is selected