ZBuff glitch in Internal renderer
Closed, ArchivedPublic

Description

System Information
windows7 64
ASUS ATI Radeon HD6870

Blender Version
Broken: (2.71 and all later)
Worked: (2.70 and all earlier)

Short description of error
i don't know how to repeat this bug and upload blend file with result

Exact steps for others to reproduce the error




Details

Type
Bug
Alexey (Inwader77) updated the task description. (Show Details)
Alexey (Inwader77) raised the priority of this task from to Needs Triage.
Alexey (Inwader77) set Type to Bug.
Bastien Montagne (mont29) triaged this task as Normal priority.Jun 4 2015, 2:20 PM

Looks like some glitch in internal engine (Cycles is not affected), probably something like float precision issue?

  • Triangulating the quad in Edit mode, is new edge is (bottom left, top right) issue persists, other edge 'fixes' it.
  • Only visible with ortho camera at this scale value too.
  • Any small scale/rotate/move (except along Z axis) fixes it.
Bastien Montagne (mont29) renamed this task from Unknown render error to ZBuff glitch in Internal renderer.Jun 4 2015, 4:33 PM

More facts:

  • Bug happens in zbuffer code of internal (somewhere in zbuffer_solid(), in zbuf.c).
  • Bug is also related to render size (render scale of 30% or less shows it, 31% and above doesn’t).

More facts:

  • Bug happens in zbuffer code of internal (somewhere in zbuffer_solid(), in zbuf.c).
  • Bug is also related to render size (render scale of 30% or less shows it, 31% and above doesn’t).

and else, if we change orto scale in camera and then return to 3.124 handly(not ctrl+Z) - working properly

Things are a bit crazy here. Will have a closer look over the weekend. Assigning to self so it's on the radars.

Wow, this is the error in clipping code I wrote in early 90ies. It is a numerical imprecision in comparing float values, and I never could solve it.

This only happens in extreme cases. Really rare.

Sergey Sharybin (sergey) closed this task as Archived.Jun 15 2015, 7:25 PM

After discussion with @Ton Roosendaal (ton) it ended up to be a numeric instability in the clipping code.

SO thanks for the report, but closing as a TODO now: http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Render#Render_Engine