Blender AgX in darktable (proof of concept)

kofa · November 16, 2025, 10:06am

Note that there’s an issue visualising the history, a kind of technical limitation. I’ve logged it here:

AgX: wrong history display for pivot relative exposure

opened 08:15AM - 16 Nov 25 UTC

### Is there an existing issue for this? - [x] I checked and did not find my is…sue in the already reported ones ### Describe the bug Root cause: - The module stores the x coordinate of the pivot in the pivot_x property, presented via the _curve/pivot relative exposure_ slider - It modifies (and on each change, recalulates) the offset and scale of the slider, so the user is presented with an EV value - In the history change popup, the **previous** value of pivot_x is interpreted using the **current** offset and scale. For example, starting from black/white -10 EV -> 6.5 EV, pivot at mid-grey (0 EV shift), and changing the black/white relative exposure to -8 EV -> 5 EV, and setting the pivot shift to 1.5 EV, then hovering over the history item 12 will show the original pivot exposure as -0.12 EV, not as 0 EV, because the old pivot_x is interpreted using the new scale and offset: <img width="758" height="470" alt="Image" src="https://github.com/user-attachments/assets/e97c6d7b-62f3-410f-9972-4c67ab2cb61d" /> Resetting the sliders and hovering over history item 13 will then show the pivot was moved from 2.06 EV to 0 EV (not the correct 1.5 EV to 0 EV): <img width="758" height="470" alt="Image" src="https://github.com/user-attachments/assets/a83811f3-d4f2-4306-a8bf-395b2db06478" /> Hovering over the previous entry, number 12 (which previously showed -0.12 EV -> 1.5 EV), shows the pivot was shifted from 0 EV to 2.06 EV: <img width="758" height="470" alt="Image" src="https://github.com/user-attachments/assets/91966c17-a851-4484-b701-f8b728c5f610" /> The field stores the pivot_x value (0..1, x coordinate of the curve's pivot) and not the EV value, and changes visualisation (offset and scale) so we don't have to modify hard limits (which was the previous solution, using those hard limits to enforce the pivot is between black and white relative exposure). This was done to address https://github.com/darktable-org/darktable/pull/19642#discussion_r2485896335. @dterrahe This is a relatively minor issue, and is probably preferable to messing with hard limits. ### Steps to reproduce See above ### Expected behavior the history should be displayed correctly ### Logfile | Screenshot | Screencast _No response_ ### Commit _No response_ ### Where did you obtain darktable from? darktable.org / GitHub release ### darktable version 7035503eb7283e1e8 ### What OS are you using? Linux ### What is the version of your OS? OS independent ### Describe your system _No response_ ### Are you using OpenCL GPU in darktable? None ### If yes, what is the GPU card and driver? _No response_ ### Please provide additional context if applicable. You can attach files too, but might need to rename to .txt or .zip _No response_

I’ll have to wait for the opinions of the core devs, as I don’t think there’s an easy fix to this.