Blender Git Loki

Bugfix for [#29327] background images: 'Not Set' displayed although image is already loaded.

Bugfix for [#29279] Cycles Displacement Panel appears when blender render engine is choosen.

Cycles: another build system tweak that might solve build problem, not sure
why this code is giving issues.

UI: modify region expand widget from floating (+) icon into a dark tab with
a light + in it.

UI:
* Add theme option to show panel header background.
* Draw panel collapse widget a bit smaller.
* Add theme option to draw icons muted.
* Code tweak: replace U.themes.first by UI_GetTheme() calls.

Fixing compile breakage (was missing an #include "BKE_camera.h" in UVProject modifier code fileâ?¦).

Camera tracking fixes:
- Fixed incorrect memory access on distoritons more than 128 pixels
- Do not use UNDO operators flags for delete proxy operator (files can't be restored form disk),
and also do not use UNDO for set as background operator (background images are storing in
3d viewport which isn't getting re-loaded on undo which can lead to incorrect users count
of movie clip user).

Camera: some more refactoring, mostly in the function that computes the camera
border, now we just get the border coordinates from comparing the viewport and
camera viewplanes.

hide overly picky warnings from 'pylint' for pep8 script, indentation edits.

More UI messages fixes and tweaks (found while translating in french).

- rename MovieTrackingMarker.enabled --> mute, to match constraints/nla/fcurves/sequencer
- report an error if an invalid BGpic arg is given to v3d.background_images.remove()

add poll function for VIEW3D_OT_camera_to_view_selected & remove some unused code.

also made it so copying camera sets the dof object to extern.

replace fabs with fabsf where both input and output are floats.

make it clearer which arguments in transform snap are return values (no functional change)

add python3 checks to avoid confusion from errors with python2.

Camera: some more code deduplication.

UI: fix issue with previous commit, could show wrong tooltip.

Camera Sensor:
* Tweak description of sensor fit property.
* Fix sensor display for auto and vertical fit.
* Fix incorrect aspect ratio for camera frame drawing.

Fix [#29018] Problem with multi-column dorpdown lists, when scrolling is enabled: the bottom-most elements are not shown.

ui_popup_block_scrolltest needs to be aware whether uiblock is flip or not, to avoid hiding irrelevant items in multi-column scrolled menus...

Camera: more code refactoring, adding a function to create CameraParams from
3d view, deduplicating the complex code for setting up the viewplane.