清华大学：《计算机图形学基础》课程教学资源（授课教案）光线跟踪，递归算法，光线求交

History of Ray Tracing (光线跟踪) • In 1980, Whitted proposed a ray tracing model, include light reflection and refraction effects. A Milestone of Computer Graphics

• Turner Whitted ，An improved illumination model for shaded display， Communications of the ACM, v.23 n.6, p.343-349, June 1980. • http://www.raytracing.co.uk/study/home.htm

• After receiving his PhD from NCSU in 1978, Turner Whitted left for Bell Labs and proceeded to shake the CGI world with an algorithm that could ray-trace a scene in a reasonable amount of time. • He only has 14 papers, and Ray tracing is his first paper

• He was elected as member of National Academy of Engineering in 2003

Ray Tracing(光线跟踪) • Introduction of ray tracing • Ray intersection(光线求交) • shadows(阴影) • Transparence and specular reflection (透明和镜面反射) • textures(纹理)

Introduction of ray tracing • Ray tracing – Because of its effectiveness, ray tracing is a widely used and very powerful rendering (drawing) technique – Why we see objects? • Light can be interpreted as a collection of rays that begin at the light sources and bounce around the objects in the scenes. • We see objects become rays finally come into our eyes

Basic Idea of ray tracing • Think of the frame buffer as a simple array of pixels, with eye looking through it into the scene • For each pixel, what can we “see”? • a ray casting from the eye through the center of the pixel and out into the scene, its path is traced to see which object the ray hits first • calculate the shading value of the point by the Phong model • continue to trace the ray in the scene to achieve reflection, refraction

Introduction of ray tracing • Features – Easy to incorporate interesting visual effects, such as shadowing, reflection and refraction, since the path of a ray is traced through the scene – Besides geometric primitives (such as spheres, cones, cubes), easy to work with a richer class of objects, including polygonal meshes, compound objects

Recursive Ray Tracing

Recursive Ray Tracing IntersectColor( vBeginPoint, vDirection) { Determine IntersectPoint; Color = ambient color; for each light Color += local shading term; if(surface is reflective) color += reflect Coefficient * IntersectColor(IntersecPoint, Reflect Ray); else if ( surface is refractive) color += refract Coefficient * IntersectColor(IntersecPoint, Refract Ray); return color; }