This week, I continued to look up literature that would be helpful for my dissertation, and took notes on them to extract the highlights.
Common modelling and rendering tools have trouble with complex, repetitive scenes with forests, leaves, grass, hair, or fur. Even in high-end productions, this kind of scene is rarely used because it takes a lot of data, is hard to model and animate, and costs a lot of money to render realistically. The author talks about how volumetric textures work well in these kinds of scenes. These basic shapes can make modelling and animation much easier. More importantly, they can be rendered quickly and with little aliasing by using ray tracing. Kajiya and Kay (1989) came up with the main idea, which is to represent a pattern of 3D geometry in a reference volume that is tiled over a surface like a regular 2D texture. In our contribution, the mapping is independent of the mesh subdivision, the pattern can be any shape, and it is prefiltered at different scales, just like MIP-mapping. Even though the model is encoded in a volumetric way, the way it is drawn is very different from how volume rendering is usually done. A volumetric texture can only be found near a surface, and the repeated parts of the reference volume, which are called texels, are distorted in space. Also, each voxel in the reference volume has a key feature that controls the reflectance function that shows the overall geometry of the voxels. This lets a single ray per pixel be used to trace very complicated scenes with very few aliasing artefacts (for the part of the scene using the volumetric texture representation). The most important technical parts of our method are figuring out the ray path and figuring out the reflectance function. （Neyret, 1998)
Neyret, F., 1998. Modeling, animating, and rendering complex scenes using volumetric textures. IEEE Transactions on Visualization and Computer Graphics, 4(1), pp.55-70.
It allows texture elements to be placed on a surface in a way that is not limited by the mesh subdivision, just like regular 2D textures.
References:
Lake, A., Marshall, C., Harris, M. and Blackstein, M., 2000, June. Stylized rendering techniques for scalable real-time 3d animation. In Proceedings of the 1st international symposium on Non-photorealistic animation and rendering (pp. 13-20).
McDonnell, R., Breidt, M. and Bülthoff, H.H., 2012. Render me real? Investigating the effect of render style on the perception of animated virtual humans. ACM Transactions on Graphics (TOG), 31(4), pp.1-11.
Rosenblum, R.E., Carlson, W.E. and Tripp III, E., 1991. Simulating the structure and dynamics of human hair: modelling, rendering and animation. The Journal of Visualization and Computer Animation, 2(4), pp.141-148.
Strothotte, T. and Schlechtweg, S., 2002. Non-photorealistic computer graphics: modeling, rendering, and animation. Morgan Kaufmann.