3D Fundamentals Tutorial 6

Get rid of those dirty back-facers, we don't serve their kind here. Also, learn the new sex move that is taking New England by storm: the Bridgeport Shocker.

Video

The tutorial video is on YouTube here.

• Recap of our problem: triangles are always drawn in the same order 0:20
• Solution: Back face culling 2:02

• Poor solution: painter's algoritm (sort the triangles back to front, draw front ones last)
• Better solution: never draw back facing triangles. For convex single objects front facing triangles will never overlap

• Using a triangle's surface normal to determine its orientation 5:15

• Just the z-component of the face normal is not good enough
• Correct approach: take the viewing vector (v1) and the face normal direction (v2)
• (viewing vector: vector from focal point to any point on the triangle in world space)
• If their dot product is negative (opposide directions), the triangle's face is towards the focal point

• How to find the face normal: the cross product 9:51

• Comparison of concepts of dot product and cross product
• v1 x v2 yields a perpendicular vector (following left hand rule in our system) with length l = area of the parallelogram spanned by v1 and v2

• The math equation for the cross product 16:13
• Getting the face normal vector of our triangles 19:26
• Implementing these concepts in our code 21:04

• The cross product operator in Vec3
• Using cull flags for the triangles 22:32

• Culling needs to be performed before the transformation to screen space 24:33
• The order of the vertices (i.e. the index lists for triangles) matters 26:04

• Use the left handed winding rule when constructing the triangle index list 27:08

• Introduction of Scene definitions and the SolidCubeClass

Downloads

The GitHub repository for the tutorial code is here.

See also

• Planet Chili Patreon
• Next in series (Tutorial 7)
• 3D Fundamentals Series