Updated skybox model to better match GZDoom's skybox. Also the sky texture was flipped horizontally.
Fixed, Visual mode: "Select with the same texture" action is now able to select sidedef parts only visible because of slopes.
Fixed, Visual mode: skybox texture was not updated after using "Open map in current wad" action.
Fixed, Visual mode: in some cases Visual camera was placed below sector's floor when "Sync camera position between 2D and 3D modes" setting was enabled.
Fixed: numeric thing flags with inverted UDMF flag defined in "thingflagstranslation" Game configuration block were lost when copy-pasting a thing.
Fixed, command line arguments: fixed a crash when loading a map from a wad with existing .dbs file.

Fixed, Visual mode: fixed D3DERR_INVALIDCALL error caused by a bug in classic skybox texture creation.
Fixed, Visual mode: aspect ratio was not updated when render area was resized.
Fixed, Visual mode: vertex handles were disappearing after using Reload Resources (F8) action.
Changed, internal: removed most of the fixed pipeline rendering code. The editor can no longer be used on a video card without Shader Model 2.0 support. 

Fixed, Visual mode: "Select with the same texture" action should not select invisible geometry (like sidedef parts hidden by slopes).
Changed, Sector drawing: default sector height is now used when the nearest sector's height is <= 0.

Fixed a crash when trying to get map title after closing Map options window.
Updated game configurations (Sector_SetPortal).

Fixed, Visual mode: "render as sky" flag was not updated for upper wall geometry when pasting textures (and in some other cases).

Added "Toggle sky rendering" action and toolbar button.
Added, MAPINFO parser: the editor now recognizes map number from classic map definition format. Hexen MAPINFO is now properly parsed.
Added, MAPINFO support: if current map definition contains map name as a text string, it will be shown in the editor's header.
Changed: "Toggle dynamic lights rendering" now toggles between "Don't show dynamic lights" and "Show dynamic lights" when used in Classic modes. 
Changed, Things mode: lowered the opacity of dynamic light radii.
Changed, (G)ZDoom text parsers: empty include files now trigger a warning instead of an error and no longer abort parsing.
Fixed, Game configurations: moved Stalagmite:5050 thing to Doom block (so the editor no longer tries to load it for non-Doom game configurations).
Fixed(?), Visual mode: probably fixed a hard-to-trigger exception when sorting translucent geometry.
Fixed, Visual mode: floor glow effect was incorrectly applied to walls (was broken in R2452).
Internal: restructured most of MAPINFO and GLDEFS parsers. Should be more maintainable now.  
Updated ZDoom ACC.
Updated zdbsp to 1.19.
Updated documentation.

Updated ZDoom_DECORATE.cfg.

MODELDEF, DECORATE, GLDEFS parsers: fixed a crash when checking a file path when said path contained unsupported characters.

Externalized most of the editor's built-in textures. You can find (and replace) them in the "[GZDB]\Textures" folder.

Fixed a typo.

Fixed a crash after pressing "Edit Selection" button in the Find and Replace window when several instances of the same map element were selected.
Redesigned the Test Map button's drop-down: test engines are now shown and behave the same way as skills and also have appropriate icons. 

Fixed, Thing/Linedef edit forms: fixed a crash during form setup when Action was either unknown or generalized.
Fixed, ANIMDEFS parser: in some cases the parser was unable to read camera texture name.

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.

Internal: joined declaration and assignment of some variables.

Fixed, GLDEFS parser: in some cases the parser was unable to detect the end of "Glow" block, which resulted in skipping the rest of the file.

Updated ZDoom ACC and ZDoom_ACS.cfg (added GetInventoryMax()).

Fixed, ACS parser: absolute and relative include paths handling was broken in R2448.

Fixed, ANIMDEFS parser: camera texture names are limited to 8 chars in ZDoom.
Fixed, Game configurations: Stalagtite:47 thing was named Stalagmite.
Changed, Game configurations: moved Stalagmite:5050 thing to the "Obstacles" category.

Some internal changes in text parsers logic.

Fixed, Script Editor: in some cases clicking on an error in the errors list didn't navigate to the error location.
Fixed, Script Editor: in some cases incorrect error line number was shown.
Fixed, Text lump parsers: fixed a crash when trying to get a filename from a quoted string with missing closing quote.
Fixed, Text lump parsers: in several cases parsing errors were ignored by overlaying data structures.
Fixed: in some cases Thing Filter thing flags were cleared when switching game configurations in the "Game Configurations" window.
Changed, PK3 reader: loading of files with invalid path chars is now skipped instead of skipping loading of the whole resource. Also more helpful warning message is now displayed.
Updated SharpCompress library to v.0.11.2.0.

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.

Changed, Renderer2D: StartOverlay() now works the same way as StartPlotter() and StartThings() (e.g. returns false when unable to render instead of throwing an Exception. Should prevent crashes for people with slow GPUs / very complex maps).

Changed, "Select Similar", "Paste Properties Special" actions properties windows, Linedefs: removed "Sidedef Properties" from Linedef flags tab.
Fixed several issues with "Synchronized Things Selection" setting:
- Things were not deselected after dragging a single sector.
- Things were not deselected after editing properties of a single sector.
- Things sector references were not updated after using "Join Sectors" and "Merge Sectors" actions.
- Things (de)selection is now applied to all things, instead of only the ones visible using current Things Filter.

Cosmetic, actions: renamed "Lower Floor/Ceiling by 8 mp" to "Lower Floor/Ceiling/Thing by 8 mp", "Raise Floor/Ceiling by 8 mp" to "Raise Floor/Ceiling/Thing by 8 mp", "Lower Floor/Ceiling by 1 mp" to "Lower Floor/Ceiling/Thing by 1 mp", "Raise Floor/Ceiling by 1 mp" to "Raise Floor/Ceiling/Thing by 1 mp", "Lower Floor/Ceiling to adjacent sector" to "Lower Floor/Ceiling/Thing to adjacent Sector/Thing", "Raise Floor/Ceiling to adjacent sector" to "Raise Floor/Ceiling/Thing to adjacent Sector/Thing".
Updated, Visual mode, "Raise Floor/Ceiling/Thing to adjacent Sector/Thing" / "Lower Floor/Ceiling/Thing to adjacent Sector/Thing" actions: sectors across targeted sectors are now taken into account when determining target height.
Updated, Visual mode, "Raise Floor/Ceiling/Thing to adjacent Sector/Thing" / "Lower Floor/Ceiling/Thing to adjacent Sector/Thing" actions: the actions can now stack things on top of other things when their bounding boxes intersect. 
Internal: cosmetic changes to shader update logic.
Internal: thing bounding box is now used when adding a thing to VisualBlockMap.

Fixed, Doom -> Hexen map format conversion: SP/Coop/MP flags were lost during Thing flags conversion resulting in Things not showing in any game mode.

Fixed, Visual mode: fixed a crash when showing Edit Vertex window when several selected vertices belonged to the same sector.

Fixed, Texture browser: "Show textures in subdirectories" setting was not applied to the root directory.
Changed, Image formats: GIF images will no longer be loaded, because (G)ZDoom doesn't support them.
Updated ZDoom_DECORATE.cfg.
Updated ZDoom_ACS.cfg.
Updated ZDoom ACC.

Fixed, Visual mode: in some cases fog density of 3d floor floors/ceilings was calculated incorrectly. 

Fixed, Visual mode, "Auto-align textures" actions, UDMF: vertical offsets of non-wrapped middle textures should not be clamped.
Fixed, Visual mode: brightness of 3d floors with "disable lighting" flag was calculated incorrectly.
Fixed, Sectors mode: 3d floor linedef indicators were not updated after using "Join Sectors" and "Merge Sectors" actions.

Fixed, Visual mode, fog rendering: things with Bright setting should still be affected by custom fade.
Updated ZDoom_DECORATE.cfg.

Added: Tab text now looks differently when appropriate script was changed.
Added: Script Editor now has it's own status bar.
Added: several files can now be opened at once when using "Open File" command.
Added: ACS scripts navigator now shows script and function arguments.
Changed: when closing a tab, previous tab is selected instead of the first tab.
Changed: SCRIPTS lump can't be compiled as a library.
Changed: external acs files can only be compiled as libraries.
Changed: when an external acs file is marked as #library, it will be saved as [library name].o alongside [filename].acs.
Fixed: files opened using "Open File" command were immediately flagged as changed.
Fixed: Script Editor was unable to navigate to error location after clicking on the error description when the error was in include file.
Updated ZDoom ACC.

Fixed, Visual mode: fixed incorrect GLDEFS glow brightness calculation for Things.
Updated ZDoom_DECORATE.cfg.