GRIME-POLYS: SANDSTONE STAIRWAY TUTORIAL - DIRT IN CONCAVE PARTS OF OBJECTS

1) Load stairway.lwo. If you do a test render(f9) you'll see the stairway object with a sandstone texture. The stairs look as if they had never been used

2) Go to the Surfaces panel and select "sandstone" as your Current Surface.

3) Click on the Advanced Options tab and add Grime-Polys under Shader Plug-ins. Another test render at this point will utilize Grime-Polys' default settings. It may take a few seconds for Grime to calculate the stairway geometry for its initial pass.

This is not the effect we are looking for so let's adjust the values to apply dirt and give the stairs an older appearance.

4) Deactivate the Color gradient by clicking on the Color tab.

5) Click on the Diffuse tab. This will select and activate the Diffuse gradient.

6) Delete the first key (located at -100) in the Effect gradient.

7) Change the value for the first key (also located at -100) in the Opacity gradient to 73.

8) Add a new key in the Opacity channel at position -61.5 (simply click in a blank area on the gradient bar, click the Add button and type -61.5 in the position requester). Set the new key value to 0.

figure 2 - Diffuse gradient settings (click image to enlarge)

A test render at this point shows that we are headed in the right direction however we are not quite there yet. The positioning of the dirt is not where it should be.

9) Use the settings below to restrict the dirt to the concave regions of the stairs.

figure 3 - Grime-Polys Crack parameters (click image to enlarge)

In the opacity gradient only its left part (the one which applies the effect to cracks) is relevant. Since the diffuse gradient is set to 0 and the opacity is in the 73 to 0 range, diffuse is gradually decreasing as we are nearing the crack.

Relevant Crack parameters:

Since the angle between steps is 90° , the only relevant parameters are those for 90° , .i.e.:

This means that Diffuse will have a constant value (taken from Start Value) within the distance of 0.1 m from the crack.

The first Diffuse value is taken from the -100 position (for edge it would be 100) of the gradient. Here in this position the diffuse gradient has the value ), but opacity is 73, therefore finally diffuse has the value of 27. Practically it would be just as good to set the entire opacity gradient to 100 and just modify the diffuse gradient, but then Grime-Polys would completely overwrite any previous textures in the Diffuse channel.

Decaying within the distance of 1 m practically means that the gradient is 'stretched' within such distance. Since the opacity gradient reaches value of 0 in the - 61 position, the effect disappears at the distance of 100 - 61 = 39 cm from the crack.

A test rendering showed that these values produce a rather exaggerated effect, therefore the Fast scaling option was set to 0.4. It decreased Max value.

figure 4 - The final product