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By Andrew Berge

Adding Dirt 2 - Making a realistic Wall with Materials vs Geometry

This scene was a simple exercise in creating realism through materials. Note that there is only 3 rectangles and 1 cube in this scene ! We could have cleaned up the junction between grass and edge with a NURB surface if desired.

example scene: dirt/projects/dirtywall.r3d

There are several elements in this scene: The wall, grass, downpipe and grass edge. Lets examine each in turn and how we achived each material.

The Wall

This object has the most materials applied:

At the "back" is our first crack - this is simply a bump image (Black and White) of a crack. Note if we map consecutive bumps to each other, the background must be black as white is high, black is low. We wanted the material to crack in, so we have used a negative value to "invert" the bump.

Next is the brick photo by itself. This is only a small section of a brick wall made "Tilable" This is best achieved in Photoshop by using the filter/offset with 'wrap around' set, to see how a material tiles. Using the stamp tool, you can make a material tile properly.

Over the brick we have put a subtle noise. Click HERE to see the values used for the noise. This adds a basic black and white noise on top of the brick to give it a slightly dirty appearance. Note we use the Scope parameter of the parallel mapping object itself (Under the Properties/spec tab) to give the noise more or less effect. Currently set quite low (0.6).

On top of the brick we have added a stain; vertical water stains that have dripped down from the top of the brickwork. This material is simply a scope material. The scope channel uses a B+W image again, with white designating the area of effect. Note we can put any material or colour in this material and the area of scope limits it to this. In this material however, we have simply used a color- hence the scope limits the colour to the area of the scope image, thus creating our vertical stains.

Then we have a simple brick bump. Note we could just as easily have added the bump with the brick material. We have used the original bump material for the bump channel, but ideally we would create a B+W bump material to emphasise the areas of interest (The mortar joints).

Last is the Graphiti. Like our stain, the graphiti is simply a scope material. The white defines the area of colour, and creates our graphiti. Note that any of these scope materials can be moved freely around the wall or duplicated to create more. Also, we have set the FINITE tags under the parallel mapping object. This limits the area of effect for this material within the boundaries set by the mapping object. Unless we wanted to tile this graphiti, generally we should use FINITE mappings for scope based objects.

Grass foreground

This object was used to show the use of the fade mapping channel. We could have just as easily mapped this material onto the brick wall using a scope instead of a fade.

This material has a fade and a colour channel used. Note that we have also used a fade constant (above). We set the fade as a constant of 1 (white) then with the image mapped to the fade channel, we use a SUBTRACT operator to essentially "invert" the alpha. We do this because RS3D uses White for transparent and black for solid in FADE channels only. Scope uses the opposite. Hence, we INVERT our alpha channel by doing this. The texture is a Targa, so the alpha is embedded into the same texture. Hence, both the colour and fade textures have the same image applied. Under Bindings tab of the fade texture, you can check that it is bound to alpha->fade. An alpha JPG would have something like ColorR->fade.

This material is then parallel mapped to the rectangle and repeated in one axis. the alpha acts as a cookie cutter and actually cuts the object itself (vs using a scope which merely limits the material).


This baseplane is simple: it has a grass texture parallel mapping tiled, then another 'Grit' material applied over that - essentially simulating some sticks over the grass - and then a duplicate copy of our Noise material from the brick to simulate a bit of un-evenness.


This object is probably more complicated than it needs to be - but shows a multiple layering of scoped materials. Note these materials make use of the scope - hence we have not globally set the colour of the object itself - hence the colour is derived from the object properties/col tab. The multiple scoped materials give a random appearance to flaking paint - all 3 of which are simply B+W scope maps and a color. We then added our noise again to give it some random discolouration.

Page updated on Tuesday, 25 February, 2003 . For feedback / model submissions or articles - please email us.
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