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spine-unity Runtime Documentation


Exporting Spine Assets for Unity

Export User Guide

You can find complete instructions in the Spine User Guide on how to

  1. Export skeleton & animation data
  2. Export texture atlases containing the images of your skeleton

Spine Unity Export for Beginners

The following shows a simple way to export Spine assets for Unity.

  1. After you have created your skeleton and animations, click on Spine Menu>Export... (CTRL+E). This opens the Export window.

  2. Choose JSON on the upper-left of the Export window.

    Note: For production you should later prefer binary skeleton exports over JSON exports, as they are smaller in size and faster to load.

  3. Check the Texture Atlas Pack checkbox. (Checking Nonessential data, Pretty print are also recommended for beginners). Be sure to have Animation cleanup disabled, otherwise keys identical to setup pose will not be exported.

    1. Click on Pack Settings below the Pack checkbox. This opens the Texture Packer Settings window.
    2. On the lower-right, look for the textbox labeled Atlas extension and make sure it is set to .atlas.txt.
    3. You're done with the Texture Packer Settings window. Click OK to close.
  4. In the Export window, pick an output folder. (Recommendation: Create a new empty folder.)

  5. Click Export.

  6. This will export three files:

    1. skeleton-name.json or skeleton-name.skel.bytes, containing your skeleton and animation data.
    2. skeleton-name.atlas.txt, containing information about the texture atlas.
    3. One or more .png files, each representing on page of your texture atlas containing the packed images your skeleton uses.

Note: For 2D Toolkit users, Step 3 (packing a .png and .atlas.txt) is not necessary. Instead, you will have the appropriate field in your SkeletonDataAsset to assign a reference to tk2dSpriteCollectionData. Please consult the Installation section on how to enable 2D Toolkit support.

Binary Export for Unity

Exporting in binary format instead of JSON will result in smaller file size and faster loading.

The following shows how to change to binary export for spine-unity.

  1. Choose Binary on the upper-left of the Export window instead of JSON.
  2. Set the Extension to .skel.bytes.

Note: spine-unity cannot load files with extension .skel. Be sure to use extension .skel.bytes.

Advanced - Automating Exports

If you have many projects, it is recommended to automate the export of your skeleton and atlas assets using the Spine command line interface. This eliminates repetitive manual work and allows for easy re-export of all projects at once, should you decide to upgrade to a newer Spine version.

You can explore examples of utilizing the command line interface here.
For example, we use this script to export all the Spine example projects and to create texture atlases:

Advanced - Single Texture Atlas Export and SkeletonGraphic

It is recommended in general to use a single-texture (single-page) atlas where possible to reduce the number of draw calls caused by additional submeshes. This is especially true for SkeletonGraphic. Due to limitations of the used Unity CanvasRenderer, SkeletonGraphic is limited to a single texture by default. You can enable Advanced - Multiple CanvasRenderers at the SkeletonGraphic component Inspector to generate a child CanvasRenderer GameObject for every submesh to raise the texture limit. For performance reasons, this is best avoided where possible. This means Skeletons used in UI shall be packed as a single-texture (single-page) atlas, rather than multi-page atlases.

If they do not fit into a single atlas page, you can pack texture atlas pages grouped by folder. This way you can ensure that each skin requires only a single atlas page.

When the images are placed in the respective folders, you can export the skeleton with the following steps:

  1. Press Ctrl+E or in the dropdown menu select Export...
  2. Enable Texture Atlas Pack and select Image Folder instead of Attachments right to it.
  3. (optional) Check in Pack Settings if under Options in the bottom right Flatten Paths and Combine Subdirectories is disabled (this is the default).
  4. Click Export.

Advanced - Premultiplied vs Straight Alpha Export

Spine offers two basic workflows via Texture Packer Settings how atlas textures can be exported:

  1. Premultiplied alpha (the default, premultiplied in Gamma color space)
  2. Straight alpha

Premultiplied alpha workflow offers some advantages over straight alpha, no additional draw calls for additive-blended attachments and better mip-map generation being two of them.

It is very important to match export and import settings correctly, see section Advanced - Premultiplied vs Straight Alpha Import for correct settings in Unity.

Importing Spine Assets into Unity

  1. Open your Unity project in the Unity Editor. It should already have a functioning spine-unity runtime in it, as described in section Installation.
  2. Open the folder of the exported files. (.json, .atlas.txt and .png)
  3. Copy the exported files (or the folder containing them) to your desired subfolder of your project's Assets folder. You can do this by dragging the exported files from an Explorer/Finder window into your desired folder in Unity's Project panel.

The spine-unity runtime will automatically generate the necessary additional Unity assets upon detecting the added files.

The following assets are generated:

  1. an _Atlas asset for the texture atlas file (.atlas.txt). It holds a reference to the material and the .atlas.txt file.
  2. a _Material asset for each texture atlas page (.png). It holds references to the shader and the .png texture.
  3. a _SkeletonData asset for skeleton data files (.json, .skel.bytes). It holds a reference to the .json or .skel.bytes file and the generated _Atlas asset. It additionally provides custom import and animation settings for your skeleton, see section Skeleton Data Asset.

Advanced - Premultiplied vs Straight Alpha Import

As described in Advanced - Premultiplied vs Straight Alpha Export, Spine offers two basic workflows of how atlas textures can be exported:

  1. Premultiplied alpha (the default, premultiplied in Gamma color space)
  2. Straight alpha

Preferences parameter Atlas Texture Settings for correct import settings

Important Note: It is very important that whenever the Premultiply alpha setting is enabled upon atlas texture export, both the Material's Straight Alpha Texture parameter and the Texture's Alpha Is Transparency setting in Unity are disabled and vice versa. The spine-unity runtime provides a Spine preferences section in Unity's Preferences window, accessible via Edit - Preferences (Unity - Preferences on Mac). It provides an Atlas Texture Settings parameter to automatically apply the proper texture and material import settings at newly imported atlas textures. Right below you can find material templates for Additive Material, Multiply Material and Screen Material. When switching to straight alpha workflow, these template material references need to be adjusted accordingly as well.

Spine Preferences - Atlas Texture Settings Spine Preferences PMA Preset Selection

Spine Preferences - Blend Mode Materials Spine Preferences Blend Mode Material Selection

When exporting atlas textures from Spine with Premultiply alpha enabled (the default), you can leave Atlas Texture Settings at PMATexturePreset, and the blend mode materials at SkeletonPMAAdditive, SkeletonPMAMultiply and SkeletonPMAScreen. If you have disabled Premultiply alpha, set Atlas Texture Settings to StraightAlphaTexturePreset and blend mode materials to SkeletonStraightAdditive, SkeletonStraightMultiply and SkeletonStraightScreen. You can also create your own TextureImporter Preset asset and blend mode material templates and assign them here. When creating your own, it is recommended to choose a name with PMA or Straight in it to reflect the used blend mode.

Whenever you see dark borders around transparent areas, or colorful stripes around your attachment images, it is very likely because of incorrect import settings.

Correct Texture Packer export and Texture and Material import settings:

  1. Premultiplied Alpha Texture Packer setting Premultiply alpha enabled,
    Unity Texture settings sRGB (Color Texture) and Alpha Is Transparency disabled,
    Unity Material parameter Straight Alpha Texture disabled.

Note: sRGB (Color Texture) was previously recommended to be enabled, however when Generate Mip Maps is enabled, this combination may lead to white seams. To avoid these artifacts and because it has no drawbacks in Gamma space, it is now recommended to keep sRGB (Color Texture) disabled with PMA textures.

  1. Straight Alpha Texture Packer setting Premultiply alpha disabled, Bleed enabled,
    Unity Texture settings sRGB (Color Texture) and Alpha Is Transparency enabled,
    Unity Material parameter Straight Alpha Texture enabled.

The default texture packer settings use Premultiply alpha. All Spine shaders that come with the spine-unity runtime are also configured to use Premultiply alpha workflow by default, they have the Straight Alpha Texture parameter disabled as default.

There might are use cases however, where you may want to use straight alpha workflow. Some of the use cases are:

  1. When using Linear color space, you must use straight alpha.
    The premultiplication is performed in Gamma space upon export, which will cause incorrect borders when converted back to Linear space on import. You will receive a log warning message when this combination is detected at a material.
  2. When you want to use a shader other than the included Spine shaders.
    Typically shaders will assume straight alpha textures, which will lead to incorrect black borders around attachment images.

Be sure to configure all textures and materials accordingly as described above when switching to straight alpha workflow. You can check or modify the current color space via Project Settings - Player - Other Settings - Color Space.

Import Troubleshooting

When something goes wrong importing your skeleton into Unity there are a number of possible causes, from incorrect Spine export settings to incorrect settings in Unity. This video will help you better understand the correct settings for many common problems during import.

Advanced - Unity SpriteAtlas as Atlas Provider

Note: It is encouraged to follow the normal Spine workflow and use sprite atlases created by Spine instead of Unity Sprite Atlas assets. Spine atlases provide superior packing, support multiple atlas pages and are less prone to problems. Use Unity's Sprite Atlas assets as an atlas provider only when you cannot use the normal Spine workflow. Also consider that you can re-pack used texture regions of a collected skin to a single atlas texture at runtime.

You can use Unity's SpriteAtlas as atlas provider as an alternative to .atlas.txt and .png files alongside a skeleton data file. Import is handled via a special Spine SpriteAtlas Import tool window accessible via Window - Spine - SpriteAtlas Import.

Spine SpriteAtlas Import Window

Steps to prepare the Sprite Atlas:

  1. Create a Sprite Atlas via Assets - Create - Sprite Atlas.
  2. Add the folder containing the Sprites to be used as attachments to Objects for Packing in the Sprite Atlas Inspector.
  3. (a) For Unity versions prior to 2018.2, please manually disable Tight Packing and enable Read/Write Enabled.
    (b) in Unity versions 2018.2 an newer, these settings are automatically adjusted for you. Spine SpriteAtlas Import Window
  4. Assign the Sprite Atlas to the Sprite Atlas property in the new Spine SpriteAtlas Import window. Additional assets are generated automatically. Spine SpriteAtlas Import Window
  5. Hit Load regions by entering Play mode to briefly switch into play mode and back again to load the region information. Your Sprite Atlas is now ready for use as a Spine atlas.

To use the atlas at a .json or .skel.bytes skeleton asset:

  1. Place the .json or .skel.bytes file in the same directory as the newly created atlas assets.
  2. Assign it to the Skeleton json/skel file property in the Spine SpriteAtlas Import window. Spine SpriteAtlas Import Window
  3. Hit Import Skeleton to generate the _SkeletonData file using the Sprite Atlas assets.

Spine Preferences

The spine-unity runtime provides a Spine section in Unity's Preferences window, accessible via Edit - Preferences (Unity - Preferences on Mac). Here you can setup default values used upon skeleton import and instantiation, as well as customize appearance and update behavior of the spine-unity runtime.

Spine Preferences Window

  • Show Hierarchy Icons. Show relevant icons next to GameObjects in the Hierarchy panel with Spine components on them.
  • Auto-reload scene components. Reloads skeleton components in the scene whenever their SkeletonDataAsset is modified. This may be slow when your scenes have large numbers of SkeletonRenderer or SkeletonGraphic components.
  • Reload SkeletonData after Play. When enabled, the shared SkeletonData of all skeletons in the active scene is reloaded (from the .json or .skel.bytes file) after exiting play-mode. This may add undesired delays, but prevents (accidental) modifications to the shared SkeletonData during play-mode carrying over its effect into subsequent plays.
  • Auto-Import Settings
    • Default Mix. The Default Mix Duration for newly imported SkeletonDataAssets.
    • Default SkeletonData Scale. The default Scale value for newly imported SkeletonDataAssets.
    • Default Shader. The default shader assigned at materials created for newly imported skeleton atlas textures.
    • Apply Atlas Texture Settings. Apply reference Atlas Texture Settings at texture importers specified below.
    • Atlas Texture Settings. Apply the selected texture import settings at newly imported atlas textures and materials. When exporting atlas textures from Spine with Premultiply alpha enabled (the default), you can leave it at PMATexturePreset. If you have disabled Premultiply alpha, set it to StraightAlphaTexturePreset. You can also create your own TextureImporter Preset asset and assign it here.
    • Additive Material. Material template for slot blend mode Additive. See SkeletonData Blend Mode Materials.
    • Multiply Material. Material template for slot blend mode Multiply. See SkeletonData Blend Mode Materials.
    • Screen Material. Material template for slot blend mode Screen. See SkeletonData Blend Mode Materials.
  • Warnings
    • Atlas Extension Warning. Log a warning and recommendation whenever a .atlas file is found.
    • Texture Settings Warning. Log a warning and recommendation whenever texture import settings are detected that could lead to undesired effects, e.g. white border artifacts.
    • Component & Material Warning. Log a warning and recommendation whenever Component and Material settings are not compatible.
    • SkeletonDataAsset no file Error. Log an error when querying SkeletonData from SkeletonDataAsset with no json or binary file assigned.
  • Editor Instantiation
  • Mecanim Bake Settings
    • Include Folder Name in Event. When enabled, Mecanim events will call methods named "FolderNameEventName", when disabled it will call "EventName".
  • Handles and Gizmos
    • Editor Bone Scale. Size of bones and similar gizmo elements displayed in the Scene view.
  • Prefabs
    • Fix Prefab Overr. MeshFilter. Global setting for the equally named skeleton component Inspector parameter, section Advanced. When the component parameter is set to Use Global Settings, this setting is used.
    • Optimize Preview Meshes. When enabled, Spine prefab preview meshes will be removed in a pre-build step to reduce build size. This increases build time as all prefabs in the project will be processed.
  • Timeline Extension - relevant for the Timeline Extension UPM Package
    • Default Mix Duration. The default value for the Default Mix Duration parameter of newly created Spine Animation State Clips.
    • Use Blend Duration. The default value for the Use Blend Duration parameter of newly created Spine Animation State Clips.

Updating Spine Assets

During development, you may frequently update your Spine skeleton data and texture atlas files. You can simply overwrite these files (.json, .skel.bytes, .atlas.txt, .png). Re-export the assets from the Spine Editor and copy the exported files to your subfolder of your project's Assets folder again, overwriting the existing files.

Unity will detect changes to these files and automatically re-import the modified assets. After re-import, all references to previously imported Spine assets will be intact and use the latest data.

Note: Unity sometimes fails to recognize file changes. In this case, locate the folder containing the Spine assets in Unity's Project panel that you want to re-import, right-click on the folder, then select Reimport from the context menu.

Skeleton Data Asset

The skeleton data asset (named with suffix _SkeletonData) stores information about the bone hierarchy, slots, draw order, animations and other data that constitutes your skeleton. Other components provided by the spine-unity runtime reference and share this skeleton data asset to animate and display a skeleton.

To inspect or modify a skeleton data asset, select it in Unity's Project panel. The Inspector panel will display all properties of the skeleton data for review and modification.

Skeleton Data

The SkeletonData section provides general import settings of the skeleton.

  • Scale. Allows you to specify a custom import scale value, affecting all skeleton instances referencing this data asset. Changing the value will immediately affect all instances of this skeleton.

    Note: When you want to precisely match e.g. 32px of artwork to 1 game unit (and the attachment images have not been scaled in Spine), you can set this Scale parameter to 1/px_per_unit. So for 32px/unit you would set Scale to 1/32 = 0.03125.

  • SkeletonData Modifiers. Provide a way for users to add additional processing to skeleton data assets after loading from a .json or .skel.bytes file has been completed. Please consult section SkeletonData Modifier Assets below for additional information.

  • Blend Modes - Upgrade. Upgrades an obsolete BlendModeMaterialAsset to the native Blend Mode Materials properties shown below.

  • Blend Mode Materials. Skeleton slots with special blend modes require additional materials. These materials are setup automatically upon import, unless a BlendModeMaterialAsset is in use with older Unity and spine-unity versions. It is recommended to upgrade an assigned BlendModeMaterialAsset via the Blend Modes - Upgrade button above, as it prevents problems with newer Unity versions. You can customize material templates for each blend mode in the Spine Preferences.

    • Apply Additive Material. When enabled, slots with Additive blend mode will also have materials generated for them. Enable this parameter when using Straight alpha workflow. It is not necessary when using PMA workflow as Normal and Additive slots can be drawn with the same PMA material.
    • Additive Materials, Multiply Materials, Screen Materials. These lists show the currently used blend mode materials for each blend mode.


Atlas references are used by the skeleton to resolve the exported image name references to the respective image areas for rendering.

Upon import the Atlas Assets array is automatically populated with one entry per atlas asset (ending with _Atlas).

In case spine-unity failed to automatically assign all required atlas assets, you can change the Atlas Assets Size to the desired amount of atlas assets and manually assign the required atlas assets to Element0 - ElementN.

Mix Settings

The skeleton data asset allows you to specify animation mix times.

Default Mix Duration allows you to enter the default mix time, in seconds.

You can define mix times for two specific animations by clicking the Add Custom Mix button in the Custom Mix Durations section of the asset and setting specific mix durations, overriding the default mix duration value above.

Components using the skeleton data asset, like the skeleton animation component, use these mix times when playing back animations.


The Preview section for a skeleton data asset allows you to inspect all bones, slots, animations, skins, and events contained in the asset.

You can playback animations via the play buttons to the left of each animation and view a live update of the respective slots via Show Attachments in the Slots section. The timeline bar shows all events as purple markers. Hover over the markers while playing to display the event name.

Use the Create Animation Reference Assets button to generate reference assets for all animations of the skeleton. An AnimationReferenceAsset acts as a Unity asset referencing a single Spine.Animation and can be assigned to component properties in the Inspector.

Skeleton Mecanim

In case you want to use Unity's Mecanim animation system instead of Spine's default animation system, you can generate and assign a Mecanim controller via Generate Mecanim Controller.

Skeleton Baking

Note: Baking is a specialized tool and is not the recommended way of using Skeletons in spine-unity! It is not used for SkeletonMecanim, SkeletonAnimation or SkeletonGraphic (UI) components! It will instead bake a Skeleton down to a less flexible Prefab with a fixed hierarchy of Transforms with MeshRenderers and compatible animation clips. A lot of Spine's features don't exist in Unity's Animation system so they can't be translated and are ignored in the process.

To open the Skeleton Baking Window, click on the gear icon at the top right of the SkeletonDataAsset Inspector and choose Skeleton Baking.

A detailled list of supported and unsupported features can be found here in SkeletonBaker.cs.

Note: Baking is not using the recently added Unity 2D animation system but the previously existing 3D MeshRenderer based system.

Texture Atlas Asset

The texture atlas asset contains information about the images used by your skeleton, namely on what texture atlas page an image is stored, as well as its UV texture coordinates on the texture atlas page.

You can view the material of the texture atlas pages by double clicking the material asset in the Materials array.

Note: You can modify the materials and textures referenced by the texture atlas asset. When modifying textures, make sure the UV texture coordinates stay valid. The SkeletonRenderer components use a normal MeshRenderer for rendering, so materials and textures are applied normally just like they would when assigned at e.g. a cube or quad. So you can replace or pre-process the textures at the materials of your Texture Atlas Asset as needed.

The Set Mipmap Bias to -0.5 button is intended for advanced users and can be used to compensate for blurry appearance when Generate Mip Maps is enabled on an atlas texture.

You can generate sprites for each image element of an atlas by pressing the Apply Regions as Texture Sprite Slices button. The generated sprites reference areas of the texture atlas image (png file) and can be used as any Unity sprite asset.

SkeletonData Modifier Assets

SkeletonData modifier assets provide a way for users to add additional processing to skeleton data assets after loading from a .json or .skel.bytes file has been completed.

SkeletonDataAsset's Inspector provides a Skeleton Data Modifiers list you can add assets to.

Writing a custom SkeletonDataModifierAsset class

You can write your own custom SkeletonDataModifierAsset class to add additional processing to skeleton data assets after loading from a .json or .skel.bytes file. SkeletonDataModifierAsset is an abstract ScriptableObject class where you can derive your own classes from.

  1. Create a new class derived from SkeletonDataModifierAsset and implement the void Apply (SkeletonData skeletonData) method. Add the CreateAssetMenu class attribute to list an entry for your class in the Asset -> Create menu.

    [[CreateAssetMenu(menuName = "TopMenu/Submenu/SubSubmenu", order = 200)]
    public class BlendModeMaterialsAsset : SkeletonDataModifierAsset {

    public override void Apply (SkeletonData skeletonData) {
  2. Create an instance of your new class by selecting your desired folder in the Project panel and selecting your newly created Asset -> Create menu entry. Assign the created asset at an element of the Skeleton Data Modifiers list of your SkeletonData asset.

Apply(skeletonData) will be called after loading data from the .json or .skel.bytes file has been completed.

BlendModeMaterialsAsset Modifier Asset (obsolete)

Note: spine-unity now provides native support for slot blend modes Additive, Multiply and Screen at each SkeletonDataAsset, with automatic setup at newly imported skeleton assets. BlendModeMaterialAssets are now obsolete and replaced by the native properties at SkeletonDataAsset. The SkeletonDataAsset Inspector provides a new Blend Modes - Upgrade button to upgrade an obsolete BlendModeMaterialAsset to the native blend modes properties. This upgrade will be performed automatically on imported and re-imported assets in Unity 2020.1 and newer to prevent reported BlendModeMaterialAsset issues in these Unity versions. spine-unity 4.0 and newer will automatically perform this upgrade regardless of the Unity version.

BlendModeMaterialsAsset is a SkeletonData modifier asset class included in spine-unity. It holds references to materials that can be used to render attachments within slots that have the Additive, Multiply and Screen blend modes assigned to them in the Spine editor.

The Material references stored in BlendModeMaterials assets are used as templates to generate new Materials that use the appropriate texture needed by the loaded attachments.

The spine-unity runtime comes packaged with a ready-to-use BlendModeMaterialsAsset named Default BlendModeMaterials. Using this included asset allows the attachments in slots with special blend modes to use the included default Multiply and Screen shaders: Spine/Blend Modes/Skeleton PMA Multiply and Spine/Blend Modes/Skeleton PMA Screen.

If you need to use different Materials or shaders or Materials with different settings, you can create new BlendModeMaterialsAssets using Create -> Spine -> SkeletonData Modifiers -> Blend Mode Materials. Then assign your Material templates to the created asset.

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