In the field of computer graphics, shaders provide an interface between lights and surfaces, giving the appearance of metal, plastic, wood, etc. As the field progresses, more and more shaders are required to simulate a wider and wider variety of materials. We present a new shader for the simulation of wood burl, a complex material used in furniture, art, car interiors, and a host of other luxury items. This shader was developed through a morphological approach - a study of the original material, its structure, and growth. Consequently, research began with a thorough look at wood burl, polished and unpolished, in an assortment of different species. We discovered the appearance can be broken into three sub-appearances - knots, curl, and a subtle undergrain. These three sub-appearances interact to create the characteristic swirls and whorls of burl. For the subtle undergrain, we used a common oak shader, added noise, and faded it into the background. We then developed a system of randomly placing points through the material to act as knots. Since the knots grow and distort the surrounding grain, we used distance-scaled forces to push the surface coordinates around and between all the knots. When the oak shader is applied, it appears to swirl and curl around the knots, much like a stream between rocks. This created the first level of curl or swirly grained wood, but one level alone appeared flat. To solve this, we procedurally blended levels of curl to give a look of increased depth. Finally, we added reflection, gloss, and other surface properties to give a look of warmth and polish. All of these properties are controlled by a set of parameters in the shader's interface. By adjusting these parameters, the user can emulate a variety of different burl types.

Celtic art contains mysterious and fascinating aesthetic elements including complex knot work motifs. The problem is that creating and exploring these motifs require substantial human effort. One solution to this problem is to create a process that collaboratively uses interactive and procedural methods within a computer graphic environment. Spline models of Celtic knot work can be interactively modeled and used as input into procedural shaders. Procedural shaders are computer programs that describe surface, light, and volumetric appearances to a renderer. The control points of spline models can be used to drive shading procedures such as the coloring and displacement of surface meshes. The result of this thesis provides both an automated and interactive process that is capable of producing complex interlaced structures such as Celtic knot work within a three-dimensional environment.

In the field of computer graphics, shaders provide an interface between lights and surfaces, giving the appearance of metal, plastic, wood, etc. As the field progresses, more and more shaders are required to simulate a wider and wider variety of materials. We present a new shader for the simulation of wood burl, a complex material used in furniture, art, car interiors, and a host of other luxury items. This shader was developed through a morphological approach - a study of the original material, its structure, and growth. Consequently, research began with a thorough look at wood burl, polished and unpolished, in an assortment of different species. We discovered the appearance can be broken into three sub-appearances - knots, curl, and a subtle undergrain. These three sub-appearances interact to create the characteristic swirls and whorls of burl. For the subtle undergrain, we used a common oak shader, added noise, and faded it into the background. We then developed a system of randomly placing points through the material to act as knots. Since the knots grow and distort the surrounding grain, we used distance-scaled forces to push the surface coordinates around and between all the knots. When the oak shader is applied, it appears to swirl and curl around the knots, much like a stream between rocks. This created the first level of curl or swirly grained wood, but one level alone appeared flat. To solve this, we procedurally blended levels of curl to give a look of increased depth. Finally, we added reflection, gloss, and other surface properties to give a look of warmth and polish. All of these properties are controlled by a set of parameters in the shader's interface. By adjusting these parameters, the user can emulate a variety of different burl types.

Celtic art contains mysterious and fascinating aesthetic elements including complex knot work motifs. The problem is that creating and exploring these motifs require substantial human effort. One solution to this problem is to create a process that collaboratively uses interactive and procedural methods within a computer graphic environment. Spline models of Celtic knot work can be interactively modeled and used as input into procedural shaders. Procedural shaders are computer programs that describe surface, light, and volumetric appearances to a renderer. The control points of spline models can be used to drive shading procedures such as the coloring and displacement of surface meshes. The result of this thesis provides both an automated and interactive process that is capable of producing complex interlaced structures such as Celtic knot work within a three-dimensional environment.

The purpose of this thesis is to develop a texture-based painterly shader that would render computer generated objects or scenes with strokes that are visually similar to paint media like watercolor, oil paint or dry media such as crayons, chalk, et cetera. This method would need an input scene in the form of three dimensional polygonal or NURBS meshes. While the structure of the meshes and the lighting in the scene would both play a crucial role in the final appearance of the scene, the painterly look will be imparted through a shader. This method, therefore, is essentially a rendering technique. Several modifiable parameters in the shader gives the user artistic freedom while overall introducing some amount of automation in the painterly rendering process.

This research develops a technique focused on shading and texturing, with an emphasis on line work and color, to emulate the unique qualities of copperplate line-engraving from 16th century cartography. A visual analysis of selected maps determines the defining characteristics adapted for three-dimensional computer generated environments. The resulting work is presented in a short time-based animation.

The purpose of this thesis is to develop a texture-based painterly shader that would render computer generated objects or scenes with strokes that are visually similar to paint media like watercolor, oil paint or dry media such as crayons, chalk, et cetera. This method would need an input scene in the form of three dimensional polygonal or NURBS meshes. While the structure of the meshes and the lighting in the scene would both play a crucial role in the final appearance of the scene, the painterly look will be imparted through a shader. This method, therefore, is essentially a rendering technique. Several modifiable parameters in the shader gives the user artistic freedom while overall introducing some amount of automation in the painterly rendering process.

This research develops a technique focused on shading and texturing, with an emphasis on line work and color, to emulate the unique qualities of copperplate line-engraving from 16th century cartography. A visual analysis of selected maps determines the defining characteristics adapted for three-dimensional computer generated environments. The resulting work is presented in a short time-based animation.

This thesis describes the development of a system for the procedural generation and painterly rendering of trees. Specifically, the rendered trees are modeled after those found in the oil landscape paintings of 19th century French painter Camille Corot. The rendering system, which is a combination of MEL-scripted Maya tools and Renderman shaders, facilitates the creation of still images that look convincingly painterly, as well as 3D animations with temporal coherence. Brush stroke properties are animated based on distance from the camera, so that traditional painting techniques for representing depth are incorporated into the computer-generated animations. During the development process, the system was generalized to apply to other structures, such as grass and rocks, and allows for the creation and rendering of entire landscapes. Several example animations were created with the system to demonstrate the ideas developed during the process and the quality of the results.

Many computer graphics applications make use of virtual humans. Methods for modelling and rendering hair are needed so that hairstyles can be added to the virtual humans. Modelling and rendering hair is challenging due to the large number of hair strands and their geometric properties, the complex lighting effects that occur among the strands of hair, and the complexity and large variation of human hairstyles. While methods have been developed for generating hair, no methods exist for generating African hair, which differs from hair of other ethnic groups. This thesis presents methods for modelling and rendering African hair. Existing hair modelling and rendering techniques are investigated, and the knowledge gained from the investigation is used to develop or enhance hair modelling and rendering techniques to produce three different forms of hair commonly found in African hairstyles. The different forms of hair identified are natural curly hair, straightened hair, and braids or twists of hair. The hair modelling techniques developed are implemented as plug-ins for the graphics program LightWave 3D. The plug-ins developed not only model the three identified forms of hair, but also add the modelled hair to a model of a head, and can be used to create a variety of African hairstyles. The plug-ins significantly reduce the time spent on hair modelling. Tests performed show that increasing the number of polygons used to model hair increases the quality of the hair produced, but also increases the rendering time. However, there is usually an upper bound to the number of polygons needed to produce a reasonable hairstyle, making it feasible to add African hairstyles to virtual humans. The rendering aspects investigated include hair illumination, texturing, shadowing and antialiasing. An anisotropic illumination model is developed that considers the properties of African hair, including the colouring, opacity and narrow width of the hair strands. Texturing is used in several instances to create the effect of individual strands of hair. Results show that texturing is useful for representing many hair strands because the density of the hair in a texture map does not have an effect on the rendering time. The importance of including a shadowing technique and applying an anti-aliasing method when rendering hair is demonstrated. The rendering techniques are implemented using the RenderMan Interface and Shading Language. A number of complete African hairstyles are shown, demonstrating that the techniques can be used to model and render African hair successfully. / GNU Ghostscript 7.07