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. 

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).

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.

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, Things mode: fixed a crash when switching to Things mode when more than 256 things were selected.

Added: holding Control key while switching to/from Visual mode will now temporarily disable position synchronization (works only when 'Synchronize camera position between 2D and 3D modes' Preferences option is enabled).
Fixed severe lock-up after finishing dragging many vertices/linedefs/sectors in Classic modes.
Updated documentation ("Synchronizing camera position").

Updated ZDoom_DECORATE.cfg (ALLOWTHRUFLAGS flag).

Added, Drag Vertices\Linedefs\Sectors\Edit Selection modes: sidedefs facing outside of current selection are now reattached/added/removed after moving the selection.
Currently this will work as intended only if the selection ends up either completely inside a single sector or completely outside of any sector. Also this logic won't be applied if the selection contains the lines with only start or end vertex selected.
Internal: some TextLabel refactoring.

Added, Sectors, Linedefs, Things modes: map element selection order of rectangular selection is now direction-dependent.

Fixed, Visual mode, UDMF: in some cases Fade color was not applied to floor and ceiling surfaces of 3d floors.
Fixed, Visual mode: in some cases not all sidedef geometry was updated when updating sectors with Plane Align (181) action. Also fixed some more unnecessary geometry updates.
Fixed, Linedefs mode, Things mode: in some cases deleting linedefs/things caused a crash when trying to update text labels.
Fixed, Draw Lines mode: in some cases the drawing was prematurely finished when "Auto-finish drawing" option was enabled.

Added, Draw Lines mode: additional guidelines and horizontal/vertical line lengths can now be displayed for currently drawn line using "Show guidelines" top menu button.
Changed, Draw Lines mode: line angles are now shown only when "Show guidelines" mode is enabled.
Fixed, Draw Lines mode: in some cases "Snap to cardinal directions" mode was snapping only to diagonals.
Fixed, Draw Lines mode: snap to geometry behaved incorrectly when "Snap to cardinal directions" mode was enabled.
Changed, Things mode: dynamic light shape is now drawn using highlight color when a dynamic light thing is highlighted.
Added more sanity checks to MODELDEFS parser.

Added, Visual mode: "Increase/Decrease Scale", "Reset Texture Offsets" and "Reset Local Texture Offsets" actions now work when used on 3d floor sides.
Fixed: CVARINFO parser was unable to parse negative int/float values.
Fixed: in some cases TextLabel text size was checked before it was calculated. 
Internal, Visual mode: reduced the number of unnecessary geometry updates when changing map geometry.
Updated ZDoom_DECORATE.cfg (atan2 and VectorAngle).

MODELDEF parser: rewrote most of the parser logic. Now it picks actor model(s) based on Frame / FrameName properties.

Fixed, Things mode: in some cases selection labels were not updated after editing a thing.
Fixed, Things mode: selection labels were positioned incorrectly on things with FixedSize setting.
Fixed, Sectors mode: fixed a crash when selecting self-referencing sector when selection labels were enabled.
Fixed, Visual mode: in some cases Auto-align texture actions were not working when "use long texture names" Map Options setting was enabled.
Fixed, MD2/MD3 loader: available animation frames upper bound check was performed incorrectly, which would cause a crash in some very special cases.
Fixed, Game configurations: most Hexen/ZDoom teleport actions use TeleportDests as teleport targets, not MapSpots.

Added, Linedefs mode, Things mode: selection numbers can now be displayed and can be toggled using the "View Selection Numbering" mode toolbar button.
Added, Linedefs mode, Things mode: sector tags can now be displayed and can be toggled using the "View Sector Tags" mode toolbar button.
Fixed, Classic modes, DB2 bug: in some cases text label size was queried before it was calculated, resulting in text labels being rendered when they shouldn't.
Updated ZDoom_DECORATE.cfg (A_LogFloat).

Changed, Texture Browser window: "All" textures group is now saved/reselected like the rest of the texture groups when closing/opening the window.
Changed, Classic modes: bigger Thing arrows are now rendered when thing sprite rendering is skipped.
Changed, Classic modes: when "Fixed Things Scale" option is enabled, thing size stays at 2x scale instead of 1x when extra bounding box is rendered.
Added Preferences -> Appearance -> "Things transparency (Things mode)" slider.
Renamed Preferences -> Appearance -> "Things transparency" to "Things transparency (other modes)".
Externalized thing bounding box and arrow texture, used to render things in Classic modes (Textures/ThingTexture2D.png).
Updated ZDoom_DECORATE.cfg (A_SetUserVarFloat, A_SetUserArrayFloat).

Added Preferences -> Appearance -> "Things transparency" slider. It controls Things transparency in all classic modes except Things mode.
Added Preferences -> Appearance -> "Hidden Things transparency" slider. It controls transparency of Things hidden by Things filter in Things mode, of all things :)

Internal: removed some duplicate casts, marked some classes is IDisposable, some streams were disposed more than once.

Added "Fixed Things Scale" setting (available in the View menu, as a button on the View toolbar and as the "Toggle Fixed Things Scale" action). When enabled, Things will no longer be scaled based on current zoom level in Classic modes, instead, thing bounding box will be drawn when appropriate (this option mimics DB1 things rendering style).
Internal: removed some remnants of fixed rendering pipeline from Renderer2D and Renderer3D.

Fixed, Things mode: Undo for things cloning by Shift-dragging them was created incorrectly (cloned things were moved to their initial position, but not removed).
Fixed, Visual mode: fixed Classic sky texture generation artifact when Bilinear filtering was enabled in Visual mode.
Fixed, Visual mode: fixed Classic sky texture generation artifact when non-power-of-2 Sky textures were used.
Fixed, Visual mode: dynamic lights flickering on surfaces nearly-perpendicular to lights centers should be much harder to trigger now.

Fixed, Map Analysis mode, "Check stuck things" check: rewritten parts of the flags checking logic to allow more accurate flag checks.
Fixed, Map Analysis mode: fixed a crash when trying to dissolve an invalid sector when one of it's linedefs referenced it on the both sides.
Fixed, Sectors mode: fixed incorrect undo description when deleting sectors.
Internal: joined declaration and assignment of some more variables.

Added, Things mode: dynamic light things light radii are now rendered (can be disabled by setting "Dynamic light mode" to "Don't show dynamic lights" on the top toolbar).
Internal, Renderer2D.RenderArrows(): only visible lines are now rendered.
Internal, API: renamed public Line3D properties: v1 to Start, v2 to End, color to Color, renderarrowhead to RenderArrowhead.

Sectors mode: removed "Move Things in Selected Sectors" toolbar button.
Sectors mode: added "Synchronized Things Editing" menu item, action and toolbar button. When enabled, things dragging will be synchronized to sector dragging. Regular, Paint and Rectangular selection will also select things (holding Alt while selecting inverts this behavior). Deleting sectors will also delete selected things.
Linedefs mode: added "Synchronized Things Editing" menu item, action and toolbar button. When enabled, selected things will be dragged when dragging linedefs. Rectangular selection will also select things (holding Alt while selecting inverts this behavior).
Changed: selection info now always displays info about all types of map elements.
Fixed: .dbs containing only current map settings was created when trying to save unchanged map. 
Fixed, Visual mode, "Copy Texture" action: when "Use long texture names" option is disabled, texture name as stored in Sidedef should be used, not the 8-char texture name.
Updated documentation.

Added "makedoorceil" game configuration property. Works the same way as "makedoortrack" and "makedoordoor", but for ceilings of door sectors. 
Changed, Game configurations: the editor no longer tries to load DECORATE/MODELDEF/VOXELDEF/GLDEFS/REVERBS lumps when "decorategames" setting is not specified / is set to empty string.
Changed, General interface: "Tools -> Reload MODELDEF/VOXELDEF" and "Tools -> Reload GLDEFS" menu items are no longer shown when current game configuration doesn't support DECORATE. 
Fixed a crash when pasting linedef/thing properties in Hexen map format.
Fixed, Visual mode: Visual Thing resources were not fully unloaded when resetting D3D device leading to crash when switching to the editor from a DX-using game engine (like ZDoom) running in fullscreen.
Fixed: in some cases, when current game configuration supported multiple script compilers, it was possible to open/create a map or change map options without selecting any script compiler.
Fixed, New Map Options window: default map name was not updated when switching game configurations.
Fixed: copied map element properties were not reset after switching to another map.
Fixed: stored textures for "Make Door" action were not reset after switching to another map.
Fixed, Game Configurations window: currently selected test engine name was not updated when pasting test engines from another configuration. 
Fixed, Game Configurations: all "Heretic in Doom map format" configurations were using Doom sector effects list.
Fixed, Game Configurations: all "Strife in Doom map format" configurations were using Doom sector effects list.

Added "Paste Properties Special" actions in "Classic" and "Visual" categories. They work the same way as "Paste Special" action.
Added: "Copy Properties", "Paste Properties" and "Paste Properties Special" options are now shown in the Edit menu if current classic mode supports them.
Changed, Paste Properties Special window: only options relevant to current map format are now displayed.
Changed, Paste Properties Special window, UDMF: all UI-managed options are now available.
Fixed: MAPINFO parser was unable to process "include" directives.
Fixed, General interface: selection info was reset to "Nothing selected" after few seconds regardless of current selection.
Fixed, Visual mode: thing bounding boxes were not updated when changing things positions using Randomize mode.
Fixed, Visual mode: event lines were displayed at incorrect height when entering Visual mode for the first time.
Fixed, Texture Browser window: when MixTexturesFlats Game Configuration option is disabled, textures/flats are no longer shown in the Used group when flats/textures with the same names are used in the map. 
Fixed(?): probably fixed an exception some users reported when trying to initialize a Classic mode after switching from Visual mode with "Sync cameras" option enabled.
Changed, Game configurations, Thing Categories: a block must have at least one thing category property to be recognized as a thing category.
Changed, Visplane Explorer: the plugin now outputs more info when it fails to initialize vpo.dll.
Cosmetic, Thing Edit window, Doom/Hexen map format: adjusted UI layout so thing flags control no longer displays scrollbars in Hexen map format.
Internal: merged methods from UDMFTools into UniFields, removed UDMFTools. 
Updated Inno Setup script (added VC++ 2008 SP1 distributive). 
Updated ZDoom_DECORATE.cfg (A_CheckBlock).
Updated documentation (added "System Requirements" page).

Visual mode: fog distance calculation is now much closer to GZDoom one.
Visual mode: thing brightness calculation when a thing is affected by floor glow is now much closer to GZDoom one.
Linedef edit window, UDMF: added "Reset front/back brightness" buttons.
Sector edit window, UDMF: added "Reset ceiling/floor brightness" buttons.
Internal, Visual mode, Things mode: persistent event lines are now updated only when map objects are changed instead of doing it on every display redraw.
Internal: improved Dictionary lookup times when using map objects and textures as keys.
Internal: added "Release + Profiler" solution configuration.
Updated ZDoom_ACS.cfg (Warp).

Added, Classic modes: default thing arguments are now taken into account when highlighting related map elements.
Probably fixed an exception when trying to check which program(s) lock the map file on Windows XP.
Changed: added an option to try to close all programs, which lock the map file when saving the map and the map file is locked (requires Windows Vista or newer).
Fixed, Preferences window: some trackbars had incorrect background color.
Fixed, General interface: in some cases status messages were almost immediately replaced by selection info messages.

Added: Auto-updater window now has "Ignore this revision" checkbox. If enabled, the window will show up only if a newer update is available. 
Fixed, Edit Selection mode: sector highlight was not updated when switching from Edit Selection to Sectors mode.
Fixed, Edit Selection mode, UDMF: in some cases texture scale Y was flipped when applying/canceling changes made in the mode.
Probably fixed a crash caused by uninitialized Association when highlighting map elements.
Fixed, Comments Panel plugin: selection info was not updated when selecting map elements in the side panel.
Fixed, Tag Explorer plugin: selection info was not updated when selecting map elements in the side panel.
Fixed a typo in Hexen_things.cfg.

Changed, Drag Linedefs/Vertices/Sectors/Things modes: line length labels are now displayed the same way as in Draw modes.
Changed, Drag Linedefs/Vertices/Sectors/Things modes: "lock movement to cardinal directions" mode (Alt-Shift-Drag) now locks movement in 4 directions instead of 8 and doesn't snap map elements to nearest grid intersections when they are not aligned to it. 
Added, Visual mode, GZDoom, DECORATE: FORCEXYBILLBOARD flag is now supported.
Added, Visual mode, GLOOME, DECORATE: FLOORSPRITE, CEILSPRITE, WALLSPRITE, ROLLSPRITE and STICKTOPLANE flags are now supported (implementation is somewhat broken ATM and probably doesn't work the same way as in GLOOME, because Windows build with most these features is nowhere to be found...).
Fixed, Visual mode: in some cases Thing brightness was calculated incorrectly.
Updated ZDoom_DECORATE.cfg.

Added, Things mode, Visual mode: event lines for InterpolationPoints are now curved when appropriate setting is enabled in the control thing (PathFollower/ActorMover/MovingCamera) [heavily inspired by Xabis' patch].
Added, Things mode: the editor will try to reconnect the path when deleting InterpolationPoints and PatrolPoints.
Internal: RenderArrows method now works the same way in Renderer2D and Renderer3D.
Internal: Line3D now has "renderarrowhead" property.

Added, Things mode: target tags are now automatically assigned when duplicating (shift-dragging) PatrolPoints and InterpolationPoints.
Fixed, ThingsMode: fixed highlighted thing disappearing when using paste action while highlighting a thing.

Changed, Things mode: things are now rendered with a bit of transparency, so things beneath other things are now visible.
Fixed, Things mode: in some cases it was impossible to highlight a thing beneath other thing when their positions were the same.
Changed, 2D modes: changed thing bounding box and arrow image.
Fixed, cosmetic, 2D modes: in some cases thing arrows were rendered bigger than thing bounding boxes.

UDMF: most of the code now supports multiple sector/linedef tags ('moreids' UDMF property). The only things left out are Tag Explorer and Tag Range plugins.

Added some boilerplate to CommentsDocker.
Internal: converted a bunch of if-elses to switches.

Sectors, Linedefs, Things modes: comment icons for appropriate map elements with comments are now rendered in these modes. This can be disabled using either the new "Toggle Comments" action, "View -> Show Comments" menu item, or "Show Comments" button on the main toolbar.

Changed, Edit Text window: the form is no longer accepted when pressing the Enter key, so line breaks can now be added easily.
Versioning: GZDB version is now determined by the first 2 revision digits, so now it's GZDB 2.3, not 1.14.

Changed, Sound Environments mode: previously selected sound environment is now automatically selected when inserting a new sound environment item. Also it's now impossible to accept the form without selecting a sound environment.
Changed, Sound Propagation mode: single-sided lines with sound zone boundary flag are now highlightable and clickable.