Date: Tue, 18 Oct 2005 17:56:03 -0400 From: Mani Thomas To: CISC640-010-05f@UDel.Edu, CISC440-010-05f@UDel.Edu Cc: Chandra Kambhamettu Subject: Ray tracing slides and the question about Shadow rays Hi All, I have uploaded the slides for Ray tracing at http://vims.cis.udel.edu/~mani/TA%20Courses/Fall05/graphics/index.html With regards to the question in class about the shadow feelers, the main difference between the illumination model and "shadow feelers"is: Given a light source and a point of intersection, it is possible that the angle is acute yet the point of intersection could be occluded by another object which lies in between the light source and the point of intersection. If there is no occlusion, the acute/obtuse angle principle can be used to decide if a point is illuminated by a light source or not (illumination ray). Please check slide 16 for the definition of illumination ray http://www.cosy.sbg.ac.at/~held/teaching/graphik/slides/rt_slides.pdf In the figure on slide 31, the point P is occluded by the cube from Light L_{2}. The angle in this case is acute but the point P is in the shadow of the cube. The only way to realize that the cube is in the path between point P and L_{2} is to determine if the shadow feeler originating from P in the direction of L_{2} is intersected by the cube. If there is an intersection, then point P falls in the cube's shadow otherwise it is an illumination ray reaching the light source. ###################################################################################### Please check Page 3, Eq (6) for a better understanding of the terms in the code on slide 29. Fast, Minimum Storage Ray-Triangle Intersection Tomas Mvller, Ben Trumbore http://www.cs.virginia.edu/~gfx/Courses/2003/ImageSynthesis/papers/Acceleration/Fast%20MinimumStorage%20RayTriangle%20Intersection.pdf