Reverse-Shadow-Mapping

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Old 06 June 2013   #1
Reverse-Shadow-Mapping

Hi,

The situation:

Model fo a simple rectangular room, single light source below the ceiling in the center of the room.

The goal:
I want to "draw shadows" on the walls, like drawing splineshapes where I want shadows, practically paintinh the room with light/shadow. Now I need to get a lampshade geometry out of that drawn shadows which in turn produces those shadows.

Is there an easy way to calculate a shadow-casting geometry out of shadows i painted as geometry?

Edit: I would also have Houdini if that is better suited.
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Last edited by Sowiedu : 06 June 2013 at 07:03 PM.
 
Old 06 June 2013   #2
Here is how I would approach it:

*After you draw the shadow splines, align a base geometry object in the general shape of the lamp shade to the light source. For example, create a Sphere, a Cylinder, a Box or whatever and make sure it is centered at the light.
*Then write a simple script that takes each knot in the wall shadow spline, shoots a ray in the direction of the light source's position and intersects with the base lamp shade geometry. You might want to even add more vertices to the shape to ensure the resolution is high enough to produce a nice projection on the geometry.
*Move each vertex of the spline to the intersection point.
*Create a clone of the lamp shade geometry.
*Create a ShapeMerge compound object from the lamp shade and pick the projected spline. Set to Cookie Cutter and check the Invert option. The result will be a piece of the lamp shade in the shape of the shadow's spline projection.
*Repeat for each spline with its own clone of the lamp shade and you should end up with the final shadow casting geometry pieces.
*Flip the normals, set to double-sided, or add a Shell modifier to make sure the light "sees" the geometry.
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Old 06 June 2013   #3
Sounds like Shadowbox in Zbrush.

http://pixologic.com/zbrush/features/shadowbox/
 
Old 06 June 2013   #4
Different way.
Uvw unwrap the wall of the room.
RendertoTexture a Lightmap of the wall shadows.
Take this into Illustrator or something that will do a bitmaptoVector conversion and converting to an .ai. Export as an .ai.
Bring it back into Max and add edit mesh.

Or increase the Lightmap contrast and use it as an opacity map on a Plane.
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Old 06 June 2013   #5
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