Probably fixed probable I/O race condition when loading images.
Fixed Visual mode stuttering due to floating point precision degradation when running the editor for several days without restarting (internal timer is now reset when saving the map or creating a new one).
Fixed, Nodes Viewer, cosmetic: Nodes Viewer window position was reset after pressing the "Rebuild Nodes" button.
Added Eternity Game configurations by printz.
Updated ZDoom_ACS.cfg (CheckClass).
Updated ZDoom ACC (CheckClass).

Updated ZDoom_DECORATE.cfg.
Updated ZDoom_ACS.cfg.
Updated ZDoom ACC.

Updated ZDoom_DECORATE.cfg.
Updated ZDoom_ACS.cfg.
Updated ZDoom ACC.

Added, Visual mode: added support for "Change Floor Brightness to this Brightness" and "Change Ceiling Brightness to this Brightness" Boom actions.
Changed, Sectors mode: "Flip Linedefs" and "Align Linedefs" actions will no longer flip single-sided linedefs with only front side.
Fixed, Script Editor: fixed a crash when trying to update script navigator combo box when switching to a never saved ACS script.

Fixed, Visual mode: "Transfer Floor/Ceiling Brightness" actions were resetting sector color on target surfaces.
Updated ZDoom_DECORATE.cfg.

Changed: LOKCDEFS keys are now sorted alphabetically.
Fixed, MAPINFO parser: blocks inside map definition block were parsed incorrectly when using new MAPINFO format.
Fixed, rendering: custom MODELDEF scale was applied incorrectly when "Stretched view in visual modes" option was enabled.
Updated ZDoom_DECORATE.cfg.
Updated GZDoom_MODELDEF.cfg.

Added "flagsrename" Game configurations property. It allows to override Thing flag names for specific things.
Added, Automap mode: added "Show locks" button (available in Hexen and UDMF map formats only).
Updated documentation.

Changed, Game Configurations: changed "basegame" value type from int to string.
Updated documentation.

Added, Visual mode: added support for ROLLCENTER sprite rendering flag, updated ROLLSPRITE implementation.
Fixed, DECORATE support: the editor was unable to determine actor sprite when the actor itself had no sprites defined and the actor it inherited from was only defined in the game configuration.
Fixed, Drag geometry modes: linedefs without both sides were removed after dragging them when "Replace with Dragged Geometry" mode was active.
Updated ZDoom_DECORATE.cfg.

Added: preview sprites are now generated from voxels. Those are used as previews and when model rendering is disabled.
Fixed: voxel support logic was outdated, which in some cases resulted in voxels not being loaded and in some weird behaviour when trying to change pitch/roll of associated things.
Updated sprites lookup logic. Now it correctly handles sprites named like NNNNA0B0.
Fixed: in some cases DECORATE parser was unable to correctly detect sprite name & frame(s) block.
Updated ZDoom_ACS.cfg.
Updated ZDoom_DECORATE.cfg.

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.

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

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).

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 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.

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).

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).

Added, DECORATE support: #region blocks are now used as thing categories ("//$Category" actor block definition overrides these). Additional category-wide special comments are now available (see documentation).
Updated documentation ("DECORATE keys" page).

Added, Sound Environments mode: sound environments of the same type are now colored using the same color.
Added, Sound Environments mode: current sound environment is now highlighted (can be toggled using "Toggle Highlight" action).
Added: Tag selectors now have up/down buttons.
Fixed, Sound Environments mode: sound environments were not updated after performing Undo/Redo actions.
Fixed, Sound Propagation mode: sound zones were not updated after performing Undo/Redo actions.
Internal: moved "Toggle Highlight" action to the core, also changed it's category to "View".
Internal: "Toggle Highlight" action state is now saved in the Program configuration.
Updated ZDoom_DECORATE.cfg (GetZAt).
Updated ZDoom_linedefs.cfg (Sector_SetPortal args).

Game configurations: added "sidedefcompressionignoresaction" property. When set to true, sidedefs will be compressed regardless of linedef action (DB2 behaviour). When set to false, sidedefs, which belong to a line with an action, will be skipped when compressing sidedefs. Default value is false.

Fixed, Visual mode: rendering effects of "Slope floor/ceiling to here" things (9500/9501) should not be applied when their arg0 is 0.

Fixed, Visual mode: "Rotate CW"/"Rotate CCW" actions should update thing-based effects when used on Things.
Added/restored, Visual mode: restored "Move Texture Left/Right/Up/Down by 8" actions, added "Move Texture Left/Right/Up/Down by Grid Size" actions (default keys are Ctrl+arrow keys).
Fixed, Game configurations: Hexen's Bell actor was missing "hangs" flag.

Updated ZDoom_DECORATE.cfg (ALLOWTHRUFLAGS flag).

Fixed, Visual mode: in some cases translucency was ignored on inner top sides of translucent 3d floors.
Internal, Script Editor: moved some setup/auto-completion logic to separate classes.
Updated ZDoom_DECORATE.cfg (A_QuakeEx).

Fixed, Visual mode: 3d floor outer sides were not updated after toggling rendering effects off, then on.
Updated ZDoom_DECORATE.cfg (GetAngle function). 

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, 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).

Fixed, Script Editor: fixed infinite loop when trying to search for empty string.
Changed, Linedefs mode: selection labels are now positioned in a less line angle obscuring way.
Changed, Draw Lines mode: text label background alpha didn't match the alpha of the labels used in other classic modes.
Updated ZDoom_ACS.cfg (SetMusicVolume).
Updated ZDoom ACC (SetMusicVolume).

Added: dynamically added side panel tabs now play notify animation when the side panel is collapsed.
Added, Game configurations, ZDoom: added Sector effect 90 (Skybox sector).

Updated ZDoom_DECORATE.cfg.

Added, Game configurations: added "Enum option + enum bits":26 action argument type. It can be used when an argument combines both exclusive and bit flag values.
Updated, Game configurations: some linedef action arguments now use type 26.
Updated documentation ("Game Configuration - Action Argument Settings").
Updated ZDoom ACC (APROP_MaxStepHeight and APROP_MaxDropOffHeight).

Fixed: fixed a crash when determining sprite angles when there were sprites for both rotated (like TESTA2A8) and non-rotated (like TESTA0) versions of the same frame.
Fixed, Tags Selector control, UDMF: in some cases tags adding/removing worked unreliably when mixed tag values were used.
Fixed, Arguments control: in some cases ending colon was not appended to argument names.
Updated ZDoom_ACS.cfg.
Updated ZDoom_DECORATE.cfg.

Added, Game configurations: added "Polyobject number":25 argument type. When set, used polyobject numbers will be displayed in the action argument dropdown.
Added, Map Analysis mode: Polyobj_ExplicitLine action was not checked by "Check polyobjects" check. 
Updated ZDoom_linedefs.cfg and Hexen_linedefs.cfg (polyobject number linedef args now have type 25).
Updated documentation ("Game Configuration - Action Argument Settings").

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).

Added, Game configurations: added "targetclasses" argument property. Can be used with argument type 14 (Thing Tag). When set, only things of given classes will be shown in the argument dropdown list in Edit Things window.
Changed, Classic modes: when "Fixed Things Scale" option is enabled, things will now switch to fixed size rendering mode when their visible size is less than 48 pixels.
Changed, Classic modes: changed the fixed size of things with FixedSize setting to 28 pixels.
Updated documentation ("targetclasses" argument property).

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).