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Color Mix "Add" mode is broken in Cycles
Closed, ResolvedPublic

Description

System Information
GNU/Linux 64bit (Intel CPU/nvidia GPU) / Fedora 23

Blender Version
Broken: 2.77 17fbce9 (git master)
Worked: 2.77a release

Short description of error
Using a Color Mix node with the first color being white and the second color black (zero on all channels) results in a Black output in "Add" mode even though 0 + 1 should be 1 not zero . my guess is that Add is doing a Mix by accident.

Exact steps for others to reproduce the error

  1. Download the File Attached bug.blend
  2. Open the file
  3. set the viewport to rendered
  4. observe the black color (it should be white)

Event Timeline

bassam kurdali (bassamk) set Type to Bug.
bassam kurdali (bassamk) created this task.
bassam kurdali (bassamk) raised the priority of this task from to Needs Triage by Developer.
Thomas Dinges (dingto) triaged this task as Confirmed, Medium priority.

In addition, from my own tests, the add mode for Color Mix seems to be broken only for the case when it gets fed a value of 1 (other values like 0.9 seem to work as intended).

that seems to be the case, at least in the example file. Well spotted (and thanks Thomas for adding Cycles project... I should have done so)

Thanks Dingto! confirming 'FIXED' both on the test .blend I uploaded and on the original tube files that exposed the bug in the first place. Great work!