The basis of this texture is an brick-like image consisting of red bricks (R=1,G=0,B=0) and green mortar (R=0,G=1,B=0) as shown below:

This image is selected with the image pattern module. Because of the way the colours have been used, the green output of this module will have a value of 1 for all green parts of the image (the "bricks") and 0 for everything else, and the red output will be 1 for all the red parts (the "mortar") and 0 everywhere else. This enables the bricks and the mortar to have different properties. The red output is multiplied by a noise function (Noise A below) fed into a 'mortar' colour map.

This has the result of applying the function only to the mortar. The green output is similarly fed into a brick-like colour map using the noise function (Noise B below).

The two results are summed to give the bricks and the mortar diffuse colour.

We want the bricks to stick out from the surface. This could be simulated using the bump height property but for a more realistic effect, true displacement mapping is used. The green output of the image module has been used to select only the bricks. This has been scaled down by 0.5 and combined with another noise function (Noise C - below) to give an extra random bumpiness. A linear transform (see below) has been applied to scale down this noise in order to add small-scale bumpiness to the bricks.

A further scaling factor of 0.05 has been applied to the combination of brick and noise bumps to reduce the displacement to a more realistic level.

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