Reduce polygons complexity by using bump mapping

 (by Jean-Sebastien Perron)

Too many polygons door

Only 6 polygon door

When do you need that kind of trick?

-You have a corridor with 10 doors.

-They are nice doors with many small details and many polygons.

-You would like to reduce the complexity of the scene.

-Polygon reduction is not an option, since you like the detailed door the way they are.

-How about replacing that 1000 polygon door with only a cube of 6 polygon.

-If you only see the door closed, you can even go as far as 1 polygon per door.

-And all this without loosing any details.

-You think I am crazy, read the tutorial.

Note

This technique can be used to replace wood molding on walls for example.

This technique is the best way to create your own 3D texture and bump maps.

We could render the depth instead with standard depth rendering of the renderer.

But, with a texture you get more control and precision.

Quick overview

-What we want is a front-view depth rendering of the "fully complex door"

-Then put the depth information of the "complex polygon door" as a bump map on a much lower polygon object.

The technique

-Create a material with a ramp texture from black to white.

-Below is an example of that concept

-On the left you can see the parallel mapping with the ramp texture applied to all the objects.

-This is exactly a depth rendering, but made manually.

The material

-The color should be black, so that the light won't interact with it.

-Put the "black to white ramp texture" in the illumination channel.

-If you are the lucky owner of Realsoft, download this optimized material jsp_depth_revealed.r3d

Mapping this material to the object to extract depth

-Map this material with a "parallel" mapping

-Map it from the side of the door

-The result should be that the more the polygon are to the front of the door, the more they are bright.

-You should adjust the mapping so that it fit perfectly the beginning of the object to the end.

Note : It does not matter if the ramp is from white to black or black to white, you can edit it later in your 2D editing application.

-Rendering the object should look like below.

-Now render the door from the front view.

-You should remove the perspective first : select orthogonal for the camera projection.

-This should give a result similar than this :

Note : What you see below has been color inverted in a 2D editing software.

Final assembly

-Then use the above as a bump texture on the low poly door.

So the low polygon object + the bump mapping made out of the complex door = an almost exact replica of the hi-polygon door.

Errors while making this tutorial

-I forgot to choose an "orthogonal camera" while rendering the depth for the texture bump map.

-The depth of the bump map could be set to match exaclty the depth of the original door (witch i did not).

-So it is possible, if you do it correctly to match exactly the original door with a texture map.

-You could also use the bump map as a displacement.