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

This tutorial shows how to produce old or dirty objects using the Grime-Polys algorithm.

Grime-Polys is used for griming objects made of fewer large plygons. The dirt / tarnish effects is applied between individual polygons. It is best for applying the efect to larger scale objects, e.g. walls of buidings. This tutorial presents a stairway.

This is the stairway object to be used.

This image presents the stairway object after a sandstone texture has been applied. The stairs look as if they had never been used.

Grime gave them an older appearance by apllying dirt to all receses. Note that the bannisters are also dirtied. The settings are as in

In the opacity gradient only its left part (the one which apllies 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 paamteres are those for 90° , .i.e.:

Start Distance:

Max Angle is 90° and Max Value is 0.1

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

Start Value:

Max Angle is 90° and Max Value is 1.0

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.

Decay Value:

Max Angle is 90° and Max Value is 1.0

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.