Fixed several cases when certain texture manipulation-related actions caused a crash when performed on not-yet-loaded textures.

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).

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.

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Fixed: voxel support logic was outdated, which in some cases resulted in voxels not being loaded and in some weird behaviour when trying to change pitch/roll of associated things.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.

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. 

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, 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 "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.

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, 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.

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.

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).

Changed, Visual mode: "Auto-align textures" and "Paste Textures Floodfill" actions now use visual mode geometry to determine whether a sidedef part should be processed. This fixes inability to apply said actions to sidedef parts only visible because of slopes.
Fixed, Visual mode: both "With same texture" and "With same height" Select modifiers are now checked when both of them are used at once (previously a sidedef part/floor/ceiling was selected when any of those matched).

Fixed, Linedefs mode: fixed inability to highlight linedefs when "Stitch geometry within" setting was set to 0.
Fixed, Visual mode: fixed a crash when performing "Auto-align textures" actions on selected sidedefs when there were also floors/ceilings selected.

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.

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").

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). 

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, 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).

Updated ZDoom_DECORATE.cfg.

Fixed, Visual mode: in some cases "Flood-fill textures" actions were not working when "use long texture names" Map Options setting was enabled.

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, Preferences -> Appearance: added "Anisotropic filtering" and "Edge Antialiasing" settings. Also regrouped some settings.
Added, "Check polyobjects" error check: added a check for matching Polyobject and Mirror Polyobject numbers of Polyobj_StartLine action.
Changed, Visual mode: anisotropic filtering is now always applied (previously it was applied only when bilinear filtering was enabled).
Fixed, Visual mode: in some cases light values were incorrectly transferred between 3d floors and regular floors/ceilings.
Fixed, ACS parser: includes for each library must be stored separately (fixes inability to compile a script with an included library, which in turn includes files already included by the script).

Fixed, Visual mode: alpha-based texture picking didn't work correctly on HiRes images.
Fixed, Visual mode: fog density was calculated incorrectly for things lit by dynamic lights.
Fixed, Edit Sector window, UDMF: "Fade" and "Light" color pickers initial values were incorrect when displaying mixed values.
Fixed, Edit Thing window, UDMF: "Color" color picker initial value was incorrect when displaying mixed values.

Changed, Draw Lines and Draw Curve modes: "Auto-finish drawing" option now works regardless of "Continuous drawing" option (previously it worked only when the latter was enabled). 
Changed: position and size of the "Errors and Warnings" window is now stored while the editor is running.
Internal: rewritten parts of long texture names support code. It now involves much less special handling.
Updated ZDoom_DECORATE.cfg (A_QuakeEx, A_CheckBlock).
Updated ZDoom_ACS.cfg (QuakeEx).
Updated ZDoom ACC (QuakeEx).

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

Game configurations: added 2 secret Sector_Set3dFloor flags. Shhh! Don't tell anybody!

Added, Draw Ellipse mode: angle setting can now be changed using "Rotate Clockwise" and "Rotate Counterclockwise" actions.
Added, Draw Line and Draw Curve modes: added "Auto-finish drawing" setting. When enabled, the modes will automatically finish drawing when currently drawn lines and already existing level geometry form a closed shape.
Changed: sector-wise linedef flipping is now done using the new "Align Linedefs" action. "Flip Linedefs" action works the same as in DB2 again.
Changed: when a map was already loaded, using "Open Map" action will use that map's directory as the starting directory.
Changed: official IWADs can no longer be saved.
Changed: disabled lump ranges/duplicate entries checks for official IWADs.
Changed: wad type is now preserved when saving a map (previously all wads were saved as PWADs).
Changed: moved Updater.exe launch much closer to the editor termination point to avoid any chance of it closing the editor before it properly closes itself.
Updated ZDoom_DECORATE.cfg (A_Blast).
Updated documentation.

Changed, cosmetic: elapsed time is now displayed after resources loading finishes.
Changed, internal: changed Clock.CurrentTime type to long.
Fixed, Tag Statistics window: in some cases the map view was not updated after selecting items in Sectors/Linedefs/Things columns. 
Fixed, cosmetic: Draw Curve mode icon was missing a shadow.