Abstract: Fast and realistic rendering of textures, characterised by a pronounced geometry, such as for example wickerwork, rattan or beach pebbles, is still a difficult and challenging problem in computer graphics. These effects can neither be simulated with 2D texture mapping nor with bump mapping. Direct geometric models or "volumetric" texturing approaches often become inevitable. All of them, however, imply excessive computational requirements. In this paper, the concept of bidirectional texture function (BTF) is introduced. A BTF permits a realistic simulation of the above mentioned effects at very low computational cost. Principles generally applied at microscale in the case of BRDFs are transposed at larger geometric scale. This allows us a direct generalisation of texture mapping and leads to many visual simulations beyond the possibilities of usual "fast" texturing techniques.