Shading and texture are used by the human visual system as ways to determine the shape of three-dimensional objects, so their use in accurately rendering objects like trees is critical. Shading is the use of color or intensity variations across an area being drawn to illustrate shape. In particular, it is used to simulate the effect of illumination on the object. Texture amounts to the surface detail of a real object. It is a difficult concept to convey simply, and yet most people understand texture implicitly. Texture is a pattern that appears on the surface of an object. It’s probably tactile but is also visual and identifies the nature of the material. Wood, cloth, metal, and stone have tactile (touch) and visual texture, and they help humans identify objects and their shapes and orientations. As a result, when we draw objects, we need to apply what we know about textures to the rendering process.