Visual mode: modified sidedef texture UV calculations to use integral linedef length to match (G)ZDoom way of rendering them.
Visual mode, UDMF: "Auto-align textures" actions now use integral linedef length when calculating texture offsets.

Added, Visual mode: added support for FLATSPRITE, ROLLSPRITE, WALLSPRITE and DONTFLIP sprite rendering flags. Removed the older GLOOME-specific implementation.
Changed, "Align Things to Nearest Linedef" action: the action can now also align things with FLATSPRITE and WALLSPRITE flags (previously only things with attached models were aligned).
Changed, "Align Things to Nearest Linedef" action: the action can now align things to the middle part of double-sided linedef, if it has a middle texture assigned. 

Added, Find & Replace mode, UDMF: added Linedef activation flags to the "Find Linedef flags" search mode flags list.
Changed, Sound Propagation mode: all sound zones are now shown when no sector is highlighted.
Changed, Sound Environments mode: the mode is now available only in UDMF map format.
Changed, Color Picker plugin: the plugin functionality is no longer available in Doom map format.
Restored the ability to create superimposed lines by dragging them with "Snap to Geometry" mode disabled.
Fixed, Sound Propagation mode: fixed a crash when a single-sided linedef had "Block Sound" flag.
Fixed, Find & Replace mode: in some cases "Find Sector/Sidedef/Linedef/Thing flags" search modes failed to find map elements with required flags.
Fixed, Edit Selection mode: in some cases incorrect geometry was created after applying multipart sector edit when "Replace with Dragged Geometry" mode was enabled.
Fixed a crash caused by eventual GDI font objects overflow.

Fixed, DB2 bug: temporary map file was growing in size after every map save/test, which eventually resulted in integer overflow exception when the file size reached ~2Gb.
Fixed, Draw Geometry modes: fixed a crash when moving the mouse cursor over a linedef while holding Alt-Shift keys when there were no new points drawn in current mode. 

Changed: single-sided linedefs with only back sidedef present are now automatically flipped when loading a map.
Changed, "Flip Linedefs" action: the action will no longer flip single-sided linedefs with only front side.
Fixed a crash when trying to determine sprite angles when images with non-sprite names, starting with expected characters, were present in the Sprites namespace.

Added, Search and Replace mode: "Find Sector Brightness" search mode now supports "<=", "<", ">=" and ">" prefixes.
Fixed, Sound Environment mode: fixed several cases when single-sided lines with only back side could cause either logic errors or crashes.
Fixed, Automap mode: fixed several cases when single-sided lines with only back side could cause logic errors.
Debug: added some debug code to WAD.Insert() to investigate the issue when lumpoffset could become negative.

Reverted some older changes to Linedef.Join(), which were made for older version of "enhanced" map element merging logic and in some cases were causing incorrect geometry to be created when using current merging logic.

Fixed: in some cases incorrect Script Configuration was used to compile scripts when performing "Save Map" / "Test Map" actions.

Fixed, Find & Replace mode: fixed a bug when "Find Sector Effect" search mode returned all map sectors when the effect to find was not generalized.
Updated ZDoom_DECORATE.cfg.

Fixed: parts of UniFileds.UniValuesMatch() logic were inverted. In some cases this resulted in incorrect behavior of "Select Similar" action in UDMF map format.
Fixed, UDMF: alpha should be ignored when applying sector fade/light color gradients.
Ported eevee's fix for incorrect sector geometry occasionally created after dragging map elements (more info: https://github.com/sirjuddington/SLADE/issues/542).

Added partial "LightMode" MAPINFO property support. Currently only "Standard" and "Doom" light modes are supported.
Updated Zandronum acc.
Updated Zandronum_ACS.cfg.

Changed, Visual mode: "Paste Selection" action (Ctrl-V) can now paste both copied textures and things, based on what was copied last.
Changed, Map Analysis mode: the view is now much more zoomed after clocking on a "Check very short linedefs" error check result.
Removed single testing engine launchable by the editor at once limitation (it worked properly only when using Test map actions anyway).
Fixed: re-did the fix for invalid geometry created when drawing very large grids from R2653, because it caused other issues.

Added, Automap mode: added "Show secrets" top menu button.
Added, Automap mode: added "Color preset" top menu drop-down.

Changed: "Unable to save the map: there are too many unique sidedefs!" error message now displays info about sidedefs counts before and after sidedef compression.
Fixed, Draw Grid mode: in some cases invalid geometry was created when drawing very large grids.
Fixed, Things mode, "Rotate Clockwise" action: fixed inability to change thing angle from 0 to 315 when "doomthingrotationangles" Game Configuration property was set to true.
Updated ZDoom_DECORATE.cfg.

Fixed, Edit Linedefs / Edit Things windows: ACS script number/name was applied only when the form was accepted while displaying a tab with Action controls.

Fixed, "Select Similar" action: in some cases map elements flags were incorrectly compared resulting in map elements not being selected when they should have been.

Added "Split Joined Sectors" Edit menu item and toolbar button. When enabled, joined sectors adjacent to drawn lines will be split.
Added "doomthingrotationangles" Game Configuration property. When enabled, editor actions related to changing thing angle will snap the resulting angle to 45 degree increments. This property is set to true for vanilla game configurations.
Fixed a crash when changing game configuration from one without Thing actions support to one with them while in Things mode.
Fixed, cosmetic, DB2 bug: current editing mode button was deselected after reloading resources.
Updated documentation ("Game Configuration - Basic Settings" page).

Fixed, Thing/Linedef/Sector info panels: in some cases map element flags were cut off by the control border. 

Added, Visual mode: added "Toggle Alpha-based Texture Highlighting" action. When enabled, 3d floor textures and middle textures on double-sided lines will be highlighted only when the crosshair points at a non-transparent pixel.
Changed: multi-part sectors are now better preserved after drawing new lines.
Changed, TEXTURES parser: patch loading errors are now ignored for textures with "NullTexture" option.
Changed, Game configurations: changed default door action arguments to better match vanilla ones.
Fixed, Actions: in some cases keyboard shortcuts involving Ctrl/Alt/Shift modifier keys were displayed incorrectly.
Fixed(?): probably fixed inability to save map wad in Slade 3.
Updated ZDoom_ACS.cfg.
Updated ZDoom_DECORATE.cfg.
Updated ZDoom ACC.

Added, Find and Replace mode: you can now search (and replace) unset sidedef/linedef/thing/sector flags.
Changed, TEXTURES parser: patch loading errors are now treated as warnings for optional textures.
Changed, TEXTURES parser: patch loading is now skipped for textures with "NullTexture" option.

Added Preferences -> Editing -> "Switch view modes when switching to the same Classic Mode" option (disabled by default). When enabled, view mode will be switched between "view floor textures" and "view ceiling textures" when activating the same 2D mode repeatedly.

Added "Next View Mode" and "Previous View Mode" actions.
Removed "Replace unused textures" checkboxes from Edit Linedefs window.
Fixed, SNDINFO parser: commented $ambient sound definitions were treated as editor comments (and still processed).

Changed, Classic modes: displayed mouse map position coordinates are now snapped to current grid size.
Updated model pitch handling to match current GZDoom implementation.
Fixed imprecise vertex coordinates generated by Draw Ellipse mode.
Fixed a resource loading exception when opened map file wad was located in the root of a Directory resource.
Internal: changed output of all InterpolationTools methods from int to float.
Fixed, Internal: InterpolationTools.InterpolateColor() delta usage was inverted.

Added 3 map geometry dragging modes (used when applying Drag Vertices/Linedefs/Sectors modes and Edit Selection mode):
- "Merge Dragged Vertices Only". Only vertex-line intersections will be processed (DB2 mode).
- "Merge Dragged Geometry". Geometry merging will be performed.
- "Replace with Dragged Geometry". Dragged geometry will replace underlaying geometry.
You can switch between these using 3 new actions, top toolbar buttons and Edit menu buttons.
Changed: activating the same 2D mode repeatedly now toggles View modes.
Renamed "Merge Geometry" action/menu item to "Snap to Geometry".
More fixes to vertex/linedef/sector dragging logic.
Updated ZDoom_DECORATE.cfg.

Fixed, ACC compiler: in some cases compilation errors contained map file path as error source instead of lump name when compiling SCRIPTS lump.
Fixed, ACC compiler: in some cases includes were processed incorrectly when compiling external acs files.

Fixed, vertex/linedef/sector dragging: in some cases middle textures were removed from dragged double-sided lines.
Fixed, ACC compiler: fixed a crash when trying to compile SCRIPTS lump of a new map, which wasn't ever saved.

Rewritten vertex/linedef/sector dragging logic. Now it processes line-line intersections. And handles more corner cases. And has less bugs. Probably.
Fixed, Edit Selection mode: texture scale was flipped when "Floor/Ceiling Transform" -> "Scale" was enabled.
Changed: a warning is no longer displayed when trying to compile an empty SCRIPTS lump.
Updated ZDoom_DECORATE.cfg.

Added SNDINFO parser. Currently only the "$ambient" command is parsed. The values are used to update the titles of "Ambient Sound NN" things and to populate "ambient_sounds" Game Configuration enum.
Fixed, DECORATE parser: actors, which used "replaces" keyword and didn't have DoomEdNum were ignored.
Updated documentation ("(G)ZDoom text lumps support" page).

Fixed, Drag Linedefs, Drag Vertices, Edit Selection modes: in some cases sidedefs were incorrectly removed when modifying a closed section of a multi-part sector.
Fixed, Drag Linedefs, Drag Vertices, Drag Sectors, Edit Selection modes: in some cases sidedef textures were not adjusted after applying the modes, leaving middle textures on double-sided lines.

Added, Edit Selection mode: Added "Adjust height" setting. It can be used to adjust floor/ceiling height of selected sectors based on the sector selection was in and the sector selection was moved into.
Removed "Adjust heights to match relatively with surrounding sector" option from Preferences -> Pasting, because sector height adjustments are now handled by Edit Selection mode.
Fixed, Sector info panel: in some cases 0 deg. floor/ceiling texture rotation was triggering texture offset/scale/rotation UI parts to be shown.
Fixed even more cases when sidedefs belonging to linedefs, which were moved on top of existing linedefs, were incorrectly reassigned when applying Edit Selection and Drag Geometry modes.
Fixed, Bridge mode: in some cases calculated floor/ceiling heights were not applied to the sectors created by the mode.
Changed, internal: changed program's CurrentCulture to InvariantCulture.

Changed, internal: made TextLabel and IRenderer2D public properties compatible with DB2 implementation.
Fixed some more cases when sidedefs belonging to linedefs, which were moved on top of existing linedefs, were incorrectly reassigned when applying Edit Selection and Drag Geometry modes.
Fixed, Map Analysis mode: error checks must be updated after switching map format.

Added "safeboundary" game configuration property. The value determines the maximum map bounding box size considered to be safe by "Check map size" error check.
Changed, Map Analysis mode: some checks are now available only under certain conditions (for example, "Check polyobjects" is now available only when the map is in Hexen or UDMF map format).
Updated documentation ("Game Configuration - Basic Settings" page).

Added: sectors are now split into multiple sectors when their shape is divided into several closed shapes by drawing new geometry or dragging existing geometry using Edit Selection and Drag Geometry modes.
Fixed: in some cases sidedefs belonging to linedefs, which were moved on top of existing linedefs, were incorrectly reassigned when applying Edit Selection and Drag Geometry modes.
Fixed: Tag Explorer update fix from R2630 was accidentally placed in an UDMF-only if-block.
Updated ZDoom_DECORATE.cfg (A_WeaponOffset).
Updated documentation ("(G)ZDoom text lumps support" page).

Fixed, Tag Explorer: in some cases (for example, when geometry was removed implicitly by dragging geometry) the list was not updated.
Fixed: in some cases generalized sector effect detection logic failed to detect a valid generalized effect.
Fixed, Action selector control: action label was not updated when changing action number from one generalized effect to another.

Fixed a crash when trying to store a custom field with "Byte Angle" type.
Fixed: in some cases custom field types stored in the map's .dbs file were not applied when loading a map. 

Fixed, Visual mode: texture offsets were updated multiple times when moving texture offsets of several extrafloor sides linked to the same control sidedef.
Fixed, Visual mode: sidedef geometry of sectors affected by "Copy Slope" effect was not updated when the source slope was modified.