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Basically, I would like to have a cross billboard (such as the one below) have it's lighting come from above it. In other words, I would like the lighting to be as if the sunshine was hitting it from above.

Grass billboard

The intention is for the billboard - Which will have a grass texture on it - To take lighting from the same direction as the terrain underneath.

The best way to do this, I believe, would appear to be with a normal map, making all 4 faces take lighting from 90 degrees upward.

Would this be possible to do with Blender?

Joehot200
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1 Answers1

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Normal maps are not necessarily for adding detail but to change the way light falls on the surface. Here is a quick example of changed normal map without changing the detail using the Normal node:

enter image description here

Here is an alternative with the normal map generated dynamically by calculating the direction between the object and the light (Can I refer to another object's properties from a Cycles node shader? Drivers? If so, how?):

enter image description here enter image description here

Watch this excellent tutorial by Zacharias Reinhardt https://www.youtube.com/watch?v=BtUS8QTsVZA&index=4&list=PLGodxM8aVtUfH9_xv4OdMM4xvBGZpggoA

in a nutshell, you have to

  1. create your full object with material first
  2. render it in ortho on a square plane
  3. generate normal map and color texture for this square projection
  4. use the normal and color textures as material for your "cross billboard"

To get a proper shadow is more complicated but can be achieved as per the great trick of part 2 of the video by Zacharias Reinhardt!

Bruno
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  • The tutorial is great, however I can't see specifically how it solves my problem, as it focuses on adding bumps to a flat surface, as opposed to making the light appear as if it's from a completely different direction. – Joehot200 Feb 05 '18 at 12:33
  • this is exactly what normal maps are for. So could you try to formulate what else you would expect? – Bruno Feb 05 '18 at 19:56
  • What I'm trying to do is make the light look like it is coming from a completely different direction. So the screenshot posted in the original post would have it's lighting from directly above.

    I am aware that normal maps are generally for adding details, however I cannot see why they're unable to be used for changing the lighting direction as well? Or am I missing something?

     – Joehot200 Feb 05 '18 at 21:56
  • normal maps just fake the direction of the "pixel" that receives the light is facing. It does not change where the light source come from. If you want the light for a specific object to be different than for other objects in your scene, you have to use some other mechanism. Ex: https://blender.stackexchange.com/questions/15337/how-do-i-make-objects-ignore-certain-light-sources . This is an old Q&A so may be it is now possible with Cycles render engine. – Bruno Feb 06 '18 at 08:26
  • I want to fake the direction of the "pixel" that receives the light, so that the pixel receives the light from above. – Joehot200 Feb 07 '18 at 10:55
  • what kind of lighting do you have in your scene? – Bruno Feb 07 '18 at 11:09
  • I have the default lighting as if a new scene was created. – Joehot200 Feb 07 '18 at 14:41
  • I still think you're confused about the role of normal maps then. Do you have normal map with the grass texture you are referring to? can you edit your post and add them please? – Bruno Feb 07 '18 at 16:13
  • I don't have a normal map with the texture. I'm sure I could add one, but I'm not looking for extra detail, I'm looking to fake the light from a different direction. It's clearly possible, as in UE4 I was able to create a custom material which could do this by faking a normal vector, however I could never get it done so that the lighting was correctly lit from above. – Joehot200 Feb 07 '18 at 18:57
  • There's no "correctly" in "lit from above" - your material is unphysical. Not because it breaks the second law of thermodynamics. It breaks time reversal symmetry and conservation of energy (= time translation symmetry). – John Dvorak Feb 08 '18 at 04:34
  • Your initial post mentioning the two crossing planes does not seem to be about respecting the real world laws of physics. You're loosing me in what you want to achieve. Can you try to illustrate it with a drawing or something? – Bruno Feb 08 '18 at 06:15