3D Fundamentals Tutorial 11

Things that are behind get covered up by things that are in front.

Video

The tutorial video is on YouTube here.

• Occlusion for multiple objects 0:24

• We used culling of triangles when drawing convex shapes
• But this doen't solve our problem with occlusion (e.g. multiple meshes in the same scene)
• One could considers the painter's algorithm, but that's inefficient and of limited use

• Solution: the z-buffer: simple, elegant & performant 2:27

• Essentially sorts triangles based on their depth at the pixel level
• Uses two 2D-arrays (for x,y coordinates): a back-buffer (of colors, in gfx in our case) as a render target, and a z-buffer (of floats) to store depth
• We initialize the z-buffer with infinity
• Whenever we want to write to the back-buffer, we check to see if z-value of the pixel we are drawing is smaller (and set the z-buffer in that case)
• This is a special sorting case 6:26

• Implementation in code 7:06

• The ZBuffer class
• Changes to the Pipeline class, if (zb.TestAndSet(x,y,z)) before the PutPixel call

• If done well, Z-testing can reduce rendering time 9:54

• Works best if geometries are sorted and drawn from front to back (more Z-test rejections)
• This is contrary to intuition and old/other techniques (e.g. in 2D: drawing sprites and tilemaps)

• Scene definitions and demo 10:58
• Differences with Hardware APIs 11:50

• These provide more options for configuring the z-buffer, such as depth comparison operators, choice of formats/types
• These typically store 1/z in the buffer, requiring corrections for depth precision (high in the near plane, low in the far plane)

• Dealing with translucent pixels and depth 13:58

• You will need to store the order of all the translucent pixels up until the first opaque one

• Stencil Buffers 14:28

• Provide more flexibility to reject pixels & have more control (general purpose bufffers)
• E.g. for UIs, HUDs, mirrors, shadow effects etc.

• Next up: vertex shaders and working towards dynamic lighting effects 15:00

Downloads

The GitHub repository for the tutorial code is here.

Paper on depth precision

See also

• Planet Chili Patreon
• Next in series (Tutorial 12)
• 3D Fundamentals Series