Anim2D

A 2D skeletal animation editor that reads Spine 3.8 and 4.0 JSON and exports Spine 4.0 JSON or binary (.skel), or Spine 3.8 JSON, with a texture packer and the FX library built in. Exports play in Spine 4.0 runtimes such as spine-unity 4.0 (or 3.8 runtimes when exported as 3.8).

.venv\Scripts\anim2d
.venv\Scripts\anim2d path\to\skeleton.json      # open a Spine 3.8 or 4.0 JSON export
.venv\Scripts\anim2d path\to\project.anim2d

Layout

Area	What it does
SETUP / ANIMATE (top left)	Switches mode (Ctrl+Tab). Each mode has its own layout; see Setup and Animate
Tool bar (bottom of the viewport)	Tools (Pose, Weights, Create), Transform (Rotate, Translate, Scale, Shear with their values and, in Animate mode, key buttons), Axes, Compensate, Options; see Tool bar. Keys: Translate W, Rotate E, Scale R, Shear Q, Pose P, Weights Shift+W, Create C, Select (all gizmos) V; any key can be changed (see Keyboard shortcuts)
Tree (right)	The hierarchy, with search, filters, an eye column, skin marks and the New… / Set Parent / Add to Skin / Split buttons; see Tree. Properties of the selection sit below it
Viewport	Right/middle drag to pan, wheel to zoom, F to frame all. View → Appearance… (the Appearance page of Settings) sets the interface theme (Studio Grey, Midnight, Charcoal, Light, Ocean), the viewport background (Default, Charcoal, Slate, Mid grey, Light, Checker or any colour) and the grid (Subtle, Blueprint, High contrast, Warm, Dots, any colour, or Off), shown live and kept between sessions; View → Grid switches the grid quickly. The FX Preset Builder uses the same theme. The zoom bar on the left has + / slider / −, 🔍 (100%) and ⛶ (fit). The selection shows a gizmo. Red border = Animate mode
Weights (left, opens with the Weights tool)	See Weights view
Properties (under the tree)	Edit the selection. In Animate mode, bone, slot colour and attachment changes become keys
Timeline (Animate mode)	Skin picker (with This skin only: the animation list shows the chosen skin's animations, matched by name, L1_intro → skin L1, plus those of no skin; choosing a skin's animation shows that skin), animation picker, play/loop, curve presets, and a Dopesheet or Graph view (see Animating)
Dopesheet, Graph (Animate mode)	Separate windows: key timing in the Dopesheet, values and bezier handles in the Graph (tabbed under the Timeline at first). Auto Key in the Timeline: on, changes become keys at once; off, changes show until you move in time and Key (K) keeps them
Moving windows	Every window (Tree, Properties, Timeline, Dopesheet, Graph, Preview, Weights) can be dragged to any side, stacked as tabs, floated or closed, and made bigger or smaller by dragging its edge (controls that no longer fit scroll); View menu reopens them and View → Reset window layout puts them back. Each mode remembers its own arrangement
Preview (left, Animate mode)	A second viewport that plays animations on its own (View → Preview, Ctrl+Shift+P), on a checkerboard, with its own zoom bar

The window uses a dark grey theme with blue highlights. The arrangement follows Spine's; the icons and drawing are Anim2D's own.

Tool bar

The bar along the bottom of the viewport shows the selected bone's (or region's) name, then:

• Tools: Pose, Weights and Create.
• Transform: Rotate, Translate, Scale and Shear.
• Each row is the tool button plus its values. Type a value and press Enter to set it.
• In Animate mode, a ◆ key button keys that property: green when it is keyed at this frame, yellow when it is keyed elsewhere.
• Axes: Local (the bone's own axes), Parent (the parent's axes) or World.
• Sets the directions of the translate gizmo's arrows.
• World also shows (and takes) world position and rotation in the Translate and Rotate values.
• Compensate (Setup mode): Bones keeps the child bones where they are when you transform a bone; Images keeps its images where they are. Works for gizmo drags, typed values and Properties.
• Options: for Bones, Images and Others (shapes and constraints), whether they can be selected in the viewport, are visible, and show their names.

Tree

• Search shows matching items with their parents. The filter buttons show or hide bones, slots, attachments and constraints. ⊞ / ⊟ expand or collapse everything.
• Eye column: click ● to hide a bone (with its child bones and slots) or a slot in the viewport, ○ to show it again. This only affects the editor; exports are unchanged.
• Skin column: 👕 marks skin-only bones and constraints. The tooltip lists the skins.
• Skin placeholders: when other skins exist, a slot lists each placeholder (an attachment name the skins fill in) with an entry per skin. Click one to edit that skin's attachment.
• New… offers what fits the selection:
• a bone or slot;
• for a slot: a skin placeholder, bounding box, clipping, path or point;
• for a bone: an IK, path or transform constraint;
• a skin, animation or event.
• Set Parent moves a bone under another bone (it keeps its place), or a slot to another bone.
• Add to Skin makes the selected bone or constraint part of the skin being edited (or one you pick).
• Split cuts a bone in two at its middle. The new end bone takes over the children, and nothing moves.
• Bone Properties also have Inherit rotation / scale / reflection. These are Spine 4.0's transform modes; reflection only counts when rotation is inherited and scale is not. Select sets whether the bone can be picked in the viewport.

Setup and Animate

Like Spine, Anim2D has two modes with their own interface:

• SETUP (blue): build the skeleton (the setup pose). There is no timeline, so the viewport is larger. Every change edits the setup pose.
• ANIMATE (red): the timeline, dopesheet and graph editor are at the bottom and the Preview is on the right. The viewport has a red border. Every change sets a key in the current animation at the current time.

Each mode remembers its own layout: show, hide or move panels in one mode and they stay that way the next time you switch to it. In Animate mode the tool strip has a key button (◆) beside Translate, Rotate, Scale and Shear that keys that property of the selected bone. The button is green when the property has a key at the current frame, yellow when it has keys elsewhere in the animation, and grey when it has none.

Gizmos

The selected bone (or region attachment) shows a gizmo. Drag a handle to change only what it controls:

The handle under the mouse turns white. Dragging the bone itself (not a handle) still works as before with the active tool. Shear is also in Properties (Shear X / Y) and has its own keys. Region attachments have no shear, as in Spine.

Typical workflow

1. File → Set images folder… to a folder of PNGs. They appear under Images.
2. Select root, press C, and drag in the viewport to create bones; each new bone becomes the parent of the next.
3. Select a bone and double-click an image to give it a slot with that image. Move, rotate or scale the attachment with the tools while in Setup mode.
4. Create an animation (Edit → New animation, or right-click Animations) and switch to Animate.
5. Scrub to a frame and pose bones with T/R/S. Keys are set automatically, or press K to key the selected bone's current pose. Change slot colour or attachment in Properties to key them.
6. Select keys and pick a curve (Linear, Stepped, Ease in/out/in-out). Drag keys to retime them.
7. File → Save writes a .anim2d project (older .rig2d projects still open). File → Export… (Ctrl+E) writes the skeleton for the game: see Export.

Animating: dopesheet, graph and preview

Dopesheet

• Click the ruler to scrub. Click a key to select it, Ctrl/Shift+click to add or remove.
• Drag in empty space to box-select keys (Ctrl/Shift adds to the selection). A plain click in empty space moves the playhead.
• Drag selected keys to retime them. Del deletes. Ctrl+A selects all keys.
• Ctrl+C copies the selected keys; Ctrl+V pastes them at the playhead. Times stay relative and curves keep their shape. Keys copied from one bone or slot paste onto the selected bone or slot, so you can reuse motion on another limb. Otherwise they go back onto the rows they came from. Pasted keys replace keys at the same times (events are added). Right-click for the same commands.
• Ctrl+wheel zooms time.

Graph (the Dopesheet / Graph switch on the timeline bar)

• Shows each value channel as a curve, for example rotate, x and y of translate, red to alpha of a colour, and IK mix and softness. It shows the rows of the selected keys, or every row of the selected bone, slot or IK constraint. Click a channel name to hide or show it.
• Drag a key point up or down to change its value. The curves around it keep their shape.
• Select a key to see its bezier handles: the outgoing handle and the previous segment's incoming handle. Drag them to shape the curve. Each channel has its own handles, as in Spine 4.0. Handle times stay inside their segment.
• To shape a linear or stepped segment, choose Curve → Bezier (edit handles in the graph). This gives straight-line handles that do not change the motion until you drag them.
• Double-click a curve to add a key there without changing the motion: the bezier segment is split in two (de Casteljau). The game samples each segment at 9 points, so after a split the motion follows the true curve slightly more closely (well under 1% of the value range).
• Wheel zooms values, Ctrl+wheel zooms time, middle-drag pans, F fits the curves.
• Deform rows show their 0 → 1 blend per segment; their handles can be edited, their values cannot.

Preview (shown in Animate mode; View → Preview)

• A second viewport, like Spine's Preview, that plays animations by itself while you edit.
• By default it plays the animation being edited and follows the editor when you switch. You can also pick a fixed animation.
• It loops at any speed (0.05–4×) and can show another skin. Bones are optional.
• Pause and drag the slider to scrub.
• Crossfade into another animation: tick it and choose the animation to switch to, when to switch and the mix duration. This is what the game does with setAnimation on one track and that mix duration in AnimationStateData.
• During the mix every property moves from the first animation's pose to the second's. Anything an animation does not key counts as the setup pose. Rotation keyed by both takes the shorter way round. Attachments switch to the second animation's (or the setup attachment) at once, as in the runtime. The status line shows how far the mix has got.
• The preview has its own view (pan and zoom only), so it never changes the project.

IK constraints

Select the bone at the end of a chain (a shin or forearm) and press Ctrl+K, or right-click it → Add IK constraint….

• Bones: one bone, or the bone and its parent (two-bone chain like thigh → shin).
• Target: an existing bone, or New target bone at the chain tip, which creates a target under the root so nothing jumps.
• Move the target bone (T) to pose the chain. Drawn in pink: a dashed line from the chain to a crosshair on the target.
• Properties (select the constraint in Constraints): target, mix, softness (two-bone), bend positive, stretch, compress and uniform (one-bone).
• Animate mode: changing mix, softness, bend, compress or stretch sets an IK key at the current time, and K keys the selected constraint. IK keys appear in the dopesheet and can be moved, deleted and given curves. Like Spine, mix and softness interpolate while bend, compress and stretch switch at each key.
• Renaming or deleting bones updates or removes the constraints that use them. Constraint orders stay contiguous (the runtime only applies orders 0..n-1).

Poses are solved with a port of the official Spine runtime's IK solver and update order, including bone transform modes and shear. The editor therefore shows the pose the game will show.

Meshes, weights and deform keys

• Create: select a region attachment and click Convert to mesh… (columns × rows grid). The mesh keeps the same name, so existing attachment keys still work, and it looks exactly like the region.
• Edit the shape (Setup mode): select the mesh (or its slot) to see the wireframe. Click a vertex, or Ctrl+click to select several, then drag with Translate, Rotate or Scale. With no vertices selected, the whole mesh is transformed. UVs stay, so the image stretches with the vertices.
• Add and remove vertices (Setup mode): Alt+click inside the mesh to add an interior vertex, or on the outline to add an outline (hull) vertex. Select vertices and press Delete (or Delete vertices) to remove them. The outline needs at least 3 vertices. New vertices take their UV, weights and deform offsets from their neighbours, so nothing visibly changes. After each change the mesh is re-triangulated: a constrained Delaunay triangulation in image space that keeps the outline, including concave outlines. Re-triangulate does this on demand, for example for meshes imported from Spine. Re-triangulating replaces any custom internal edges from Spine.
• Vertex drag mode (Setup mode):
• Reshape: vertices move and the image stretches with them.
• Edit mesh: vertices and their UVs move together, so the image stays put and only the mesh layout changes.
• UVs only: vertices stay and the image slides underneath them.

New UVs are clamped to the image.

• Weights: Bind to bones… weights every vertex to the chosen bones by distance (up to 4 per vertex). Select one vertex to fine-tune it: set a bone's weight exactly and the others share the rest, or Add bone. Unbind returns to an unweighted mesh. The mesh never jumps while you do this.
• Deform keys (Animate mode): drag vertices to key the mesh shape at the current time. Other vertices keep their current deform. Key deform keys the current shape; Key setup shape keys no deform. Deform keys appear as slot / attachment · deform rows in the dopesheet and can be moved, deleted and given curves.
• Binding, unbinding or changing weights converts existing deform keys so the animation keeps its shape. Adding, reparenting or reordering bones keeps weights attached to the right bones. Deleting a bone that still weights a mesh is refused until you unbind or remove that weight.

Transform and path constraints

Right-click a bone → Add transform constraint… or Add path constraint… (or right-click Constraints). Choose the constrained bones and the target.

• Transform constraint: the bones copy the target bone's rotation, position, scale and shear, each by its own mix (0–1). Properties sets the offsets and the modes: Local copies the target's local values instead of its world transform, and Relative adds them instead of matching. A dotted line joins the bones to their target.
• Path constraint: the bones are placed in order along the path attachment of the target slot.
• Position is where the first bone sits (percent of the path, or fixed length).
• Spacing separates the bones: length (bone length plus spacing), fixed, percent or proportional.
• Rotate mode: tangent follows the path direction; chain aims each bone at the next; chainScale also stretches the bones to fit.
• Mix rotate/X/Y blend the constraint in.
• Animate mode: the mixes (and a path's position and spacing) are keyed like IK; K keys the selected constraint. The keys show in the dopesheet and the graph editor.
• Update order: constraints are applied in the order listed under Constraints. Right-click → Update earlier/later. Orders stay contiguous, because the runtime skips gaps.
• Renaming or deleting a bone or slot updates or removes the constraints and skins that use it.
• Solver: every constraint is solved with a port of the official 4.0 runtime, so the editor shows the game's pose. This includes the runtime's own quirk in the scale of local, absolute transform constraints.

Pose tool

Pose (P): drag a bone and it rotates, together with its parent, so that its tip follows the mouse, like a temporary IK chain.

• Shift-drag rotates the bone alone; Ctrl-drag uses the whole chain up to the root.
• Only rotations change: the setup pose in Setup mode, rotate keys in Animate mode.
• One drag is one undo step.

Shapes: paths, bounding boxes, clipping and points

Right-click a slot → Add shape. Shapes are drawn over the images (the game does not draw them), and in Setup mode they are edited directly:

• Path: smooth points with handles (squares). Dragging a point carries its handles. Alt+click adds a point (beyond the last point it extends the path), Delete removes the selected points. Closed joins the ends; Constant speed moves bones along it evenly. The curve lengths the runtime needs are recomputed after every edit.
• Bounding box (hit areas for the game) and clipping polygon: drag vertices, Alt+click on an edge adds one, Delete removes the selected ones.
• Clipping: clips the slots drawn after it, up to and including Clip until slot (or the last slot). The viewport, the renders and the exports clip the same way.
• Point: a position and direction (for example a gun muzzle). Drag it with Translate and aim it with Rotate.

Skins

Skins list under Skins in the hierarchy. Double-click a skin (or Edit and show this skin) to edit it: the viewport then shows that skin on top of the default skin, and new attachments go into it.

• Give an attachment in a skin the same name as one in another skin (the slot's setup attachment or attachment keys). Each skin then shows its own image in that slot, as in Spine.
• Skin bones and constraints: list them in the skin's Properties, or tick Skin only on a bone or constraint. They are only active while a skin that lists them is.
• New, rename, duplicate and delete skins. Move to skin moves an attachment and its deform keys to another skin.
• Deform keys belong to an attachment of a skin, so the dopesheet shows those of the edit skin.
• Linked meshes (common in imported rigs) draw with their parent mesh's shape and, with deform inheritance on, play the parent's deform keys.

Weight painting and mesh tracing

• Weights (Shift+W): select a mesh and paint in the viewport; the Weights view opens with the tool.
• Weights show as a heat map: red = 1, blue = 0.
• Add and Subtract move the weight towards 1 or 0 by Strength. Replace sets it to Strength. Smooth evens each vertex out with its neighbours.
• The brush fades towards its edge. The other bones share the remaining weight in proportion.
• The mesh never moves while you paint, and deform keys keep their shape.
• One stroke is one undo step. Unweighted meshes are weighted to their slot bone first.
• Trace… (Properties of a region or an unweighted mesh): builds a mesh from the image's alpha.
• Detail is how far the outline may stray from the edge (lower gives more vertices).
• Padding grows the outline outwards. Alpha threshold sets which pixels count as opaque.
• Interior spacing adds vertices inside.
• The traced mesh shows the image exactly where the region or mesh did.

Weights view

The Weights tool (Shift+W) opens the Weights view, laid out like Spine's.

• Mode: Add, Subtract, Replace or Smooth.
• Strength: how much each dab changes the weight.
• Size: the brush radius in screen pixels.
• Feather: how soft the brush edge is. The dashed inner ring is the full-strength core.
• Smooth: evens all weights out with their neighbours, once. Auto: weights from the distance to the bound bones, as Bind does. Prune: removes weights below a value and renormalises.
• Pies draws each vertex's bone weights as a pie in the bones' colours. Overlay colours the mesh by the painted bone's weights (red = 1, blue = 0). Selected limits painting, Smooth and Auto to the selected vertices.
• Bones: the bones the mesh is bound to, each with its colour.
• Click a bone to paint it; the 🔒 column locks a bone so its weights do not change.
• With the Weights tool, selecting a bone in the Tree or Ctrl+clicking it in the viewport also picks it. The mesh stays the one being weighted.
• Bind binds the mesh to the bones you tick. An unweighted mesh gets automatic weights; a weighted one gets the bones added with no weight, ready to paint.
• Remove takes the chosen bone out. Its weight goes to the vertex's other bones (or the nearest bound bone), and nothing moves.
• Update Bindings: after you move bones in Setup mode the bound mesh moves with them. Update Bindings puts the mesh back where it was at the last Bind and binds it to the bones where they are now.
• Anim2D remembers the bind pose for this session only. After reopening a project, Bind again first.

FX inside the editor

FX → Insert FX into skeleton… (Ctrl+I, or right-click a bone → Insert FX here…)

• Pick any built-in preset or one of your Spine templates, tune it with the same controls as the FX Preset Builder, and choose the bone, animation and start time.
• The effect is merged into the skeleton with its own prefixed bones and slots. Its root follows the chosen bone, its slots draw on top, and its images are copied to images/<instance>/. Its keys are added to the chosen animation; existing keys are never changed.
• It is ordinary skeleton data afterwards: select fx_…_root to move or aim it, edit or retime its keys, or delete it.
• One Undo removes the whole insertion. Image files already copied stay in the images folder.
• FX → Import FX template from Spine export… registers a Spine-edited effect; FX → Open FX Preset Builder opens the standalone tool.

Rigging and animation tools

File menu

Autosave (off by default) writes <project>.anim2d.autosave next to a saved project that has changes, every N minutes. The project file itself changes only when you save.

Settings

File → Settings… (F12) opens every preference in one window, a page per topic. OK keeps the changes; Cancel puts Appearance back the way it was.

Updates. Installed copies check GitHub once a day, a few seconds after starting. When a release is out, a dialog shows its notes, and an ⬆ Update to … button stays in the status bar. Install update downloads the installer, checks it against the release's SHA-256 checksums, asks to save your project, closes Anim2D, and the installer updates it in place, keeping the apps and shortcuts you chose, then starts it again. Skip this version stops it being offered until a newer one is out; Help → Check for Updates… always shows it. If there's no connection, the daily check stays quiet and Settings → Updates says what went wrong. The portable program downloads the new portable program next to itself instead; running from source never checks by itself.

Keyboard shortcuts

Edit → Keyboard Shortcuts… (Ctrl+Alt+K) lists every command with its key. Click a key and press the new one, or clear it; a key used twice is refused. Reset all restores the defaults. The keys are kept between sessions; Help → Shortcuts shows the current ones. The Help menu also has Check for Updates…, Report a Bug… and About Anim2D.

Space (Edit → Deselect) clears the selection: bones, slots, attachments, mesh vertices and selected keys. In a text box Space still types a space.

Spine projects (.spine)

File → Import Project… opens Spine editor project files directly, so you can carry on with a project without exporting it from Spine first.

• Spine 3.8.x (tested with 3.8.55 and 3.8.75): bones, slots, skins and skin folders, region, mesh, linked mesh, bounding box, path and clipping attachments with weights, IK, transform and path constraints with their order, events, and every animation timeline (bones, slot colours and attachments, deform, draw order, events, constraints).
• Spine 4.2.x (tested with 4.2.43): the same setup data, and animations with their 4.x per-channel bezier curves, stepped keys, colours, attachments, deform, IK and draw order. 4.2's constraint order and physics constraints are not imported.
• Setup values come from the setup pose, even if the project was saved in Animate mode. Attachments whose Export box is off in Spine are left out, as Spine's export does.
• The images folder is the one the project names (usually ./images/ next to the .spine).
• A project with several skeletons imports the first one.
• Point attachments and other classes none of the test projects used are not decoded yet; such a project reports what it could not read instead of importing partly.
• Other Spine versions (2.x, 3.0–3.7, 4.0, 4.1): export JSON from Spine and import that instead.

Spine does not publish the .spine format. Anim2D reads it from how Spine writes its projects, and checks the result against Spine's own exports: see Verification.

Export

File → Export… (Ctrl+E). Choose a format on the left; its options are on the right.

• Save / Load write and read the dialog's settings as a file.
• Each format remembers its own settings between exports.
• Open after export opens the file (or the folder, for many files) when done.

Data: JSON and Binary

3.8 export: some Spine 4.0 curves and timelines have no exact 3.8 form. Examples are split X/Y timelines, separate RGB and alpha timelines, and curves whose handles differ per channel. These are converted to extra linear keys, so 3.8 plays the same motion within 0.01 px or degree. The export lists what was converted.

Image and video

Formats: GIF, PNG (one file per frame, or packed into an atlas), APNG, PSD (one layer per frame, the first on top), JPEG (one file per frame), WebP, AVI (Motion JPEG, or uncompressed with alpha), MOV (PNG with alpha, or JPEG) and MP4 (H.264).

• Frames use the editor's renderer. Blend modes are approximate.
• AVI, MOV and PSD files are written by Anim2D itself; MP4 uses the H.264 encoder Windows provides, through Qt Multimedia. No extra software is needed.
• JPEG-based video is padded to an even width and height with the background colour.
• Anim2D has no audio, so videos have no sound.

Unity bridge

File → Unity Bridge… exports straight into a Unity project for spine-unity: choose the project folder (the one with Assets/), a folder in Assets (default Assets/Spine), the spine-unity version (4.0 or 3.8; detected when spine-unity is installed), premultiplied alpha and atlas scale. Each skeleton goes to its own subfolder as <name>.json, <name>.atlas.txt and the atlas PNGs, which spine-unity turns into a SkeletonData asset. With Export to Unity every time the project is saved on, saving also exports; Export to Unity (Ctrl+Alt+E) exports at any time. The settings are saved in the project.

Unity notices the new files when it comes to the front. Install auto-refresh script in Unity adds Assets/Editor/Anim2DBridge.cs, which refreshes Unity's assets after each export even while it is in the background (delete the file to stop it).

Texture Packer

File → Texture Packer… (Ctrl+P) packs a folder; Pack settings… in the Export dialog uses the same settings.

Region names are the image paths (parts/arm), as the Spine runtimes look them up. Spine's Polygons packing is not available; Grid packing is.

What is supported

Verification

Automated (pytest):

• Editing operations, renames, cascading deletes and reparenting.
• Animate-mode keying, the viewport tools, and save/load.
• Rendering, and the editor window and Insert FX dialog.
• Exports load in the official spine-ts runtimes (4.0.31 for 4.0, 3.8 for 3.8), with bone positions matching the editor within 0.05 px.
• Spine 4.0 support is checked against the official runtimes:
• The pose evaluator matches the 4.0 runtime on Esoteric's 4.0 exports (spineboy, raptor).
• 3.8 → 4.0 conversion poses identically in both runtimes.
• 4.0 → 3.8 conversion stays within the baking tolerance.
• Binary: .skel files written by Anim2D load in the official 4.0 SkeletonBinary. Every sample of every animation matches the same data loaded from JSON: bone matrices, slot colours, attachments, draw order, IK, mesh vertices, skins and events. This holds for Esoteric's spineboy-ess, spineboy-pro and raptor-pro 4.0 exports, and for a test rig that uses everything else:
• split timelines, and rgb/alpha/two-colour keys;
• transform and path constraints with keys;
• linked meshes, points, clipping, and skin bones and constraints;
• negative draw-order offsets and audio events.
• Mixing: the Preview's crossfade matches the official 4.0 AnimationState within 0.05 px for bones and meshes, and exactly for attachments and colours. This is tested on five crossfades of Esoteric's spineboy and raptor 4.0 exports, including the IK and weighted-mesh rig.
• Graph editing: changing a key's value keeps the curve shapes around it, and so does a paste. Adding a key on a bezier, linear, stepped or deform segment leaves the motion in place: within 0.3 px in the official runtime, and within 0.05 px for mesh vertices.
• UI: box select, copy/paste onto another bone, dragging values and handles (one undo step per drag), double-click insert and the preview are driven with mouse and key events offscreen.
• Weights view: the feather falloff, locked bones keeping their weights, selected-only painting, Smooth, Auto (same as Bind), Prune, Remove (nothing moves), Update Bindings (the mesh returns to its bind-time place), the panel and the zoom bar are tested.
• Tool bar and tree: typed values (also in World axes), translating along Local and World axes, compensation of children and images (one undo step), the selectable/visible options, the eye column, search and filters, New…, Set Parent, Add to Skin, Split, skin placeholders and the inherit flags are tested.
• Gizmos and modes: dragging each gizmo handle changes only its axis or property, in Setup (setup pose) and Animate (keys) modes. The Setup and Animate layouts and the key buttons' colours are checked.
• Atlas: page pixels match the source images (rotated, stripped, scaled and premultiplied). The official 4.0 TextureAtlas + AtlasAttachmentLoader produce region and mesh UVs that land on exactly the page pixels the packer wrote.
• Constraints and skins: the solver matches the official 4.0 runtime within 0.05 px, both in positions and in bone matrices, on:
• Esoteric's spineboy-pro (aim transform constraints), tank-pro (path constraint with chain, 6 transform constraints), vine-pro (chainScale path) and stretchyman-pro (4 path constraints);
• goblins-pro in both skins, and mix-and-match-pro (34 skins, 59 skin bones, skin constraints, linked meshes) in two skins;
• crossfades with constraints;
• rigs covering what the examples do not: local/relative transform constraints, fixed and proportional spacing, closed, non-constant-speed and weighted paths, and path deform keys.
• Round trip: importing those rigs and exporting them as 4.0 JSON or .skel gives the same poses and draw order in the official runtime as the original files.
• Editing: constraint editing, the Pose tool, shape and path editing, skins, weight painting (one undo step per stroke; the mesh does not move) and tracing are tested. Traced vertices sit exactly where the region drew those image points, and every opaque pixel lies inside the outline (within the detail).
• Animation export: GIF, WebP and APNG frame counts and loops are checked, and the MP4 is H.264 and plays back at the right length.
• Export dialog: frame planning (repeat, range, last frame, skins), GIF pause and loop, PSD layers, JPEG backgrounds, packed frames, crop and size are tested. The AVI (both encodings) and MOV (both encodings) files are decoded by Qt Multimedia's FFmpeg backend: 1.0 s long, with the right background colour.
• Packer: pages pass the official spine-ts 4.0 atlas loader with the new settings (padding X/Y, no edge padding, alias, duplicate padding, bleed, repeat, format). Unpacking a packed atlas gives back every source image pixel for pixel (within rounding when premultiplied), and 3.8 atlases unpack too.
• Spine projects: all 57 .spine files on the test machine (Spine's 3.8.55 examples, 3.8.75 game projects and a 4.2.43 project) import and pass validation. The examples' bones, slots, skins, meshes, weights and constraints equal their JSON exports, and their animations, played by the official spine-ts 3.8 runtime, match Spine's full-precision .skel exports to 0.03 px at every sampled time. The 4.2 project matches its 3.8 copy (bones exactly, poses within the copy's baking error).
• Data: animation clean up keeps every pose, nonessential data is left out, JavaScript output has unquoted names, and Import Data merges and undoes.
• Spineboy import → export reproduces the original bones, slots, skins, events and the run animation.
• An FX inserted into spineboy's shoot is hidden during its delay, visible during the effect and hidden afterwards, and the character still draws.
• IK poses match the official runtime within 0.05 px for every bone. The rigs tested cover:
• two-bone and one-bone chains, out-of-reach targets, softness, stretch/compress/uniform;
• keyed mix and bend with curves;
• mirrored, non-uniformly scaled and sheared parents;
• chained constraints;
• Esoteric's raptor-pro (9 IK constraints) across its walk, roar, jump and gun-grab animations.
• Mesh world vertices match the official runtime within 0.05 px, both for meshes built and keyed in Anim2D (weights, IK, deform keys with curves) and for every raptor-pro mesh, including weighted meshes with deform keys in walk and roar.
• Converting to a mesh, binding, unbinding, editing weights and bone edits leave every vertex in place, and existing deform keys keep their shape.
• Adding vertices (interior or outline) and removing outline points that lie on a straight edge leave the rendered image unchanged, in the setup pose and at deform keys. An Edit mesh drag leaves the image in place. After vertex adds and removes on a weighted, deform-keyed mesh, vertices still match the official runtime within 0.05 px.
• The triangulation is tested for exact area coverage, kept outline edges, every vertex used, the Delaunay property, concave and clockwise outlines, and rejection of crossing or overlapping outlines, points outside the outline and duplicate points.

Not yet tested:

• importing an export into the Spine editor;
• playback in a Unity project with spine-unity (not yet verified);
• the C# (spine-csharp) runtime itself. The tests use spine-ts, which mirrors it field for field. One known spine-ts 4.0.31 difference: its JSON reader keeps the first transform key's mix shear Y for every later key. Its binary reader and the Java/C# readers are correct, and Anim2D follows them.

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