Inconsistent scroll behaviour

Is there an existing issue for this?

• I checked and did not find my issue in the already reported ones

Describe the bug

In general, scrolling up (away from the user) or to the right should increase size (of shapes: masks, effect feedback circles, feathering...) or values (e.g. on sliders), while scrolling down (towards the user) or to the left should do the opposite. Unfortunately, this is not always the case.
The following is an analysis of the current situation, performed with the aid of coding agents. I will review the UI findings later, when I have time. I can confirm several of them are correct (e.g. denoise (profiled)).

The effect of OS-level scroll reversals (e.g. "natural scroll") is not taken into account. Plus, we have a setting to reverse some adjustments (probably in response to "natural scroll"), which is mentioned below. More human verification / clarification is needed.

The purpose of this report is to start a discussion and come up with a plan.

1. Direction primitives

• dt_gui_get_scroll_unit_deltas() / dt_gui_get_scroll_deltas() (src/gui/gtk.c): GDK_SCROLL_UP → delta_y = -1, GDK_SCROLL_DOWN → +1, GDK_SCROLL_LEFT → delta_x = -1, GDK_SCROLL_RIGHT → +1.
• Scalar-collapse caveat: dt_gui_get_scroll_delta() and dt_gui_get_scroll_unit_delta() (src/gui/gtk.c:597, 609) return delta_x + delta_y. Any handler built on these treats LEFT like UP and RIGHT like DOWN, collapsing the two axes to one scalar.
• GtkEventControllerScroll "scroll" signal (used by bauhaus, histogram): UP → dy < 0, RIGHT → dx > 0 (GTK convention).
• Mask-shape handlers get a boolean up, mapped through dt_mask_scroll_increases() (src/develop/imageop_gui.c:317). The config key masks_scroll_down_increases (default false) inverts the whole family when enabled.

2. Controls that accept scroll

Class	Source	Behavior
Bauhaus sliders	src/bauhaus/bauhaus.c::_widget_scroll, _popup_scroll	vertical UP = increase; horizontal RIGHT = decrease (§4)
Bauhaus comboboxes	same	UP = previous entry, DOWN = next (ordered cycling)
Gradient sliders	src/dtgtk/gradientslider.c::_gradient_slider_scroll_event	vertical conforms; RIGHT violates via scalar helper
Notebook tabs	src/gui/gtk.c::_notebook_scroll_callback	UP = next, DOWN = previous (ordered cycling)
Preset cycling	src/develop/imageop.c::_presets_scroll_callback	ordered
Module-group buttons	src/libs/modulegroups.c::_scroll_group_buttons	ordered
Wrapped-panel content / resize	src/gui/gtk.c::_resize_wrap_scroll, _scroll_wrap_height	plain = pan; Shift+Alt = resize (§4)
Curve point editors	src/iop/basecurve.c::_scrolled, src/iop/tonecurve.c::_scrolled, src/iop/rgbcurve.c::_area_scrolled_callback	UP = raise point; RIGHT violates via scalar helper
Level handles	src/iop/levels.c, src/iop/rgblevels.c	UP = raise handle
Color-correction saturation	src/iop/colorcorrection.c::dt_iop_colorcorrection_scrolled	UP = increase; RIGHT violates
Zone-system bar	src/iop/zonesystem.c::dt_iop_zonesystem_bar_scrolled	UP = more zones; RIGHT violates
Geotagging datetime	src/libs/geotagging.c::_datetime_scroll_over	UP = +1; RIGHT violates
Timeline	src/libs/tools/timeline.c::_lib_timeline_scroll_callback	plain = pan; Ctrl = zoom (UP = zoom-in)
LUT list	src/iop/lut3d.c::_mouse_scroll	ordered list navigation
Darkroom image / second window	src/views/darkroom.c::scrolled, _second_window_scrolled_callback	UP = zoom-in; 2nd-window RIGHT violates via scalar helper
Lighttable / culling	src/dtgtk/thumbtable.c::_event_scroll, src/dtgtk/culling.c::_event_scroll	pan / zoom (UP = bigger thumbs)
Histogram / scope strip	src/libs/histogram.c::_eventbox_scroll_callback, motion handler at src/libs/histogram.c:344-348 → src/iop/exposure.c::_exposure_proxy_handle_event	drag UP/RIGHT brightens (conforms); scroll UP/RIGHT darkens in both the exposure and the black-point regions (§4)
Vectorscope	src/libs/scopes/vectorscope.c::_vec_eventbox_scroll	width is categorical cycling; rotation UP = counter-clockwise (§4)
OSM map	src/views/map.c::_view_map_scroll_event	base-map zoom conforms; active-location ROI violates (§4)

3. Module-specific / in-canvas widgets

Module	Widget	Source	Status
mask: circle / ellipse / brush / path / gradient / object / group	shape overlay (size / feather / opacity / rotation)	src/develop/masks/{circle,ellipse,brush,path,gradient,object,group}.c::*_events_mouse_scrolled	default conforms (user-invertible)
liquify	warp stamp (size / strength / angle)	src/iop/liquify.c::scrolled	conforms (inherits mask preference)
graduated density	density (Ctrl) / hardness (Shift)	src/iop/graduatednd.c::scrolled	conforms
tone equalizer	on-image tone cursor	src/iop/toneequal.c::scrolled	conforms
retouch	wavelet-decomposition bar	src/iop/retouch.c::rt_wdbar_scrolled	conforms
perspective correction	near-line selection radius	src/iop/ashift.c::scrolled	conforms
color zones (curve mode)	selected node y / Ctrl = graph zoom	src/iop/colorzones.c::_area_scrolled_callback	conforms
color equaliser graph	forwards to bauhaus slider / notebook	src/iop/colorequal.c::_area_scrolled_callback	inherits slider behaviour
contrast equaliser	feedback-circle diameter (mouse_radius)	src/iop/atrous.c::area_scrolled	violates — UP shrinks
denoise (profiled)	feedback-circle diameter	src/iop/denoiseprofile.c::denoiseprofile_scrolled	violates
raw denoise	feedback-circle diameter	src/iop/rawdenoise.c::rawdenoise_scrolled	violates
lowlight vision	feedback-circle diameter	src/iop/lowlight.c::lowlight_scrolled	violates
color zones (edit-by-area)	feedback-circle diameter	src/iop/colorzones.c::_area_scrolled_callback	violates
monochrome	virtual-filter size (p->size)	src/iop/monochrome.c::_monochrome_scrolled	violates

4. Convention violations

4.1 Vertical (UP → decreases)

Each of these is an independent callback; the formula differs but the direction error is the same.

Widget	Source	Effect on UP
Contrast-equaliser feedback circle	src/iop/atrous.c::area_scrolled	radius shrinks
Denoise (profiled) feedback circle	src/iop/denoiseprofile.c::denoiseprofile_scrolled	radius shrinks
Raw-denoise feedback circle	src/iop/rawdenoise.c::rawdenoise_scrolled	radius shrinks
Lowlight feedback circle	src/iop/lowlight.c::lowlight_scrolled	radius shrinks
Color-zones edit-by-area circle	src/iop/colorzones.c::_area_scrolled_callback (area branch)	radius shrinks
Monochrome filter size	src/iop/monochrome.c::_monochrome_scrolled	filter shrinks
Map active-location ROI (delta1 / delta2)	src/views/map.c::_view_map_scroll_event	ROI shrinks
Histogram/scope exposure region (scroll)	src/libs/histogram.c::_eventbox_scroll_callback → src/iop/exposure.c::_exposure_proxy_handle_event	exposure decreases → image darkens
Histogram/scope black-point region (scroll)	same	black value increases (shadows clipped harder) → image darkens
Wrapped-panel resize (Shift+Alt+scroll)	src/gui/gtk.c::_resize_wrap_scroll (line count), _scroll_wrap_height (pixel height)	size / line count shrinks
Vectorscope harmony rotation	src/libs/scopes/vectorscope.c::_vec_eventbox_scroll	rotation decreases (counter-clockwise)

4.2 Horizontal (RIGHT → decreases) — all stem from scalar-collapse helpers

Any handler that reads scroll through dt_gui_get_scroll_delta(), dt_gui_get_scroll_unit_delta() or literally dx + dy treats RIGHT like DOWN. Known instances:

• Bauhaus sliders — src/bauhaus/bauhaus.c::_widget_scroll, _popup_scroll
• Gradient sliders — src/dtgtk/gradientslider.c::_gradient_slider_scroll_event
• Base / tone / RGB curve point scroll — src/iop/{basecurve,tonecurve,rgbcurve}.c
• Color-correction saturation — src/iop/colorcorrection.c::dt_iop_colorcorrection_scrolled
• Zone-system bar — src/iop/zonesystem.c::dt_iop_zonesystem_bar_scrolled
• Geotagging datetime fields — src/libs/geotagging.c::_datetime_scroll_over
• Darkroom second-window zoom — src/views/darkroom.c::_second_window_scrolled_callback

In addition, histogram exposure decreases on RIGHT independently of the scalar helpers, because _eventbox_scroll_callback passes dy - dx directly.

Horizontal scroll only surfaces on devices that emit it (trackpads, tilt wheels).

5. Non-violations worth flagging

• Mask preference masks_scroll_down_increases (src/develop/imageop_gui.c::dt_mask_scroll_increases): if the user toggles it on, every mask-shape and liquify scroll inverts; default is off so the default behaviour conforms.
• Scope drag vs. scope scroll: the intuitive convention over a scope is "UP/RIGHT (in the scope's natural bright direction) brightens the image", not "UP/RIGHT increases the underlying slider value". Drag already follows this — each scope's get_exposure_delta returns a positive delta when the pointer moves towards the bright side (histogram: offset_x / width; horizontal waveform: -offset_y / height; vertical waveform: offset_x / width), and _exposure_proxy_handle_event negates the delta for black-point so that both regions brighten together. The scroll path instead passes dy - dx, giving delta = -1 for UP and for RIGHT, which darkens both regions — that is the §4 violation. This convention applies only when the widget in question is a scope; scrolling over the actual exposure/black sliders in the exposure module is governed by the regular "UP = increase slider value" rule.
• Lighttable "images per row" (Ctrl+scroll): UP decreases the numeric count but means larger thumbnails ("zoom in"); not a violation in spirit.
• Color-zones Ctrl+scroll graph zoom (zoom_factor *= 1 - 0.1*delta_y): UP zooms in. Conforms.

Steps to reproduce

Not specific -- use scroll in various modules

Expected behavior

No response

Logfile | Screenshot | Screencast

No response

Commit

No response

Where did you obtain darktable from?

darktable.org / GitHub release

darktable version

5.5.0+1010~gc0800819c8

What OS are you using?

Linux

What is the version of your OS?

Ubuntu 25.10

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

Start by reading the scroll direction helpers in src/gui/gtk.c and the listed callbacks across src/bauhaus, src/dtgtk, src/iop, src/libs, and src/views. Narrow the report to a decided set of violations, then verify each affected control's vertical and horizontal behavior; done means the agreed controls follow the documented convention and are manually checked.