Week 9 - Friday

 What did we talk about last time?  Area lighting  Environment mapping  Blinn and Newell's method  Sphere mapping  Cubic environmental mapping

 The reflectance equation we have been studying is:  The full rendering equation is:  The difference is the L o (r(p,l),-l) term which means that the incoming light to our point is the outgoing light from some other point  Unfortunately, this is all recursive (and can go on nearly forever)

 Real-time rendering uses local (non-recursive) lighting whenever possible  Global illumination causes all of our problems (unbounded object-object interaction)  Transparency  Reflections  Shadows

 We can describe a path that light L makes to the eye E using the following notation OperatorDescriptionExampleExplanation * Zero or more S*S* Zero or more specular bounces + One or more D+D+ One or more diffuse bounces ? Zero or one S?S? Zero or one specular bounces | Either/or D|SS Either a diffuse or two specular bounces () Group (D|S)* Zero or more of diffuse or specular

 Shadow terminology:  Occluder: object that blocks the light  Receiver: object the shadow is cast onto  Point lights cast hard shadows (regions are completely shadows or not)  Area lights cast soft shadows  Umbra is the fully shadowed part  Penumbra is the partially shadowed part

 A planar shadow occurs when an object casts a shadow on a flat surface  Projection shadows are a technique for making planar shadows:  Render the object normally  Project the entire object onto the surface  Render the object a second time with all its polygons set to black  The book gives the projection matrix for arbitrary planes

 We need to bias (offset) the plane just a little bit  Otherwise, we get z fighting and the shadows can be below the surface  Shadows can be draw larger than the plane  The stencil buffer can be used to fix this  Only opaque shadows work  Partially transparent shadows will make some parts too dark  Z-buffer and stencil buffer tricks can help with this too Hard to see example from Shogo: MAD

 Another fix for projection shadows is rendering them to a texture, then rendering the texture  Effects like blurring the texture can soften shadows softer  If the light source is between the occluder and the receiver, an antishadow is generated

 True soft shadows occur due to area lights  We can simulate area lights with a number of point lights  For each point light, we draw a shadow in an accumulation buffer  We use the accumulation buffer as a texture drawn on the surface  Alternatively, we can move the receiver up and down slightly and average those results  Both methods can require many passes to get good results

 You can just blur based on the amount of distance from the occluder to the receiver  It doesn't always look right if the occluder touches the receiver  Haines's method is to paint the silhouette of the hard shadow with gradients  The width is proportional to the height of the silhouette edge casting the shadow

 More on shadows  Ambient occlusion

 Keep working on Project 3  Finish Assignment 4!  Due tonight by midnight!  Keep reading Chapter 9