AssimpImporter: import skin data

src/MagnumPlugins/AssimpImporter/AssimpImporter.conf

@@ -49,6 +49,17 @@ mergeAnimationClips=false
 # key/value pair with the default node transformation
 removeDummyAnimationTracks=true
 
+# Maximum amount of joint weights per vertex to import as vertex attributes.
+# A value of 0 disables any limit, any other value implicitly enables
+# aiProcess_LimitBoneWeights. This can be changed only before the first file
+# is opened.
+maxJointWeights=4
+
+# Merge all skins into a single skin. Since Assimp exposes one skin for each
+# mesh with joint weights, this is useful for getting a single skin covering
+# all meshes in the file. This can only be controlled on a per-file basis.
+mergeSkins=false
+
 # AI_CONFIG_* values, can be changed only before the first file is opened
 ImportColladaIgnoreUpDirection=false
 

src/MagnumPlugins/AssimpImporter/AssimpImporter.h

@@ -197,7 +197,7 @@ with @ref InputFileCallbackPolicy::LoadTemporary and
 @ref InputFileCallbackPolicy::Close is emitted right after the file is fully
 read.
 
-Import of skeleton, skin and morph data is not supported at the moment.
+Import of morph data is not supported at the moment.
 
 The importer recognizes @ref ImporterFlag::Verbose, enabling verbose logging
 in Assimp when the flag is enabled. However please note that since Assimp
@@ -228,7 +228,6 @@ verbosity levels in each instance.
     prints a warning and normalizes them. Can be disabled per-animation with
     the @cb{.ini} normalizeQuaternions @ce option, see
     @ref Trade-AssimpImporter-configuration "below".
--   Skeletons and skins are not supported
 -   Morph targets are not supported
 -   Animation tracks are always imported with
     @ref Animation::Interpolation::Linear, because Assimp doesn't expose any
@@ -250,6 +249,18 @@ verbosity levels in each instance.
     these versions.
     Because it's impossible to detect the actual brokenness, the warning is
     printed even if the imported data may be correct.
+-   Original skins are not exposed by Assimp, instead each mesh with joint
+    weights produces its own skin. Skin names will be equal to their
+    corresponding mesh names. A consequence of this is that Assimp only
+    imports joint weight attributes for one skin and ignores all other
+    skins targetting the same mesh.
+-   You can request to merge all mesh skins into one using the
+    @cb{.ini} mergeSkins @ce option. Duplicate joints (same object index and
+    inverse bind matrix) will be merged and joint ids in vertex attributes
+    adjusted accordingly. When this option is enabled,
+    @ref skinCount() always report either @cpp 0 @ce or @cpp 1 @ce and
+    the merged skin has no name. This option needs to be set before opening
+    a file because it affects skin as well as mesh loading.
 
 @subsection Trade-AssimpImporter-behavior-materials Material import
 
@@ -287,9 +298,6 @@ verbosity levels in each instance.
 -   Custom mesh attributes (such as `object_id` in Stanford PLY files) are
     not imported.
 -   Texture coordinate layers with other than two components are skipped
--   For some file formats (such as COLLADA), Assimp may create a dummy
-    "skeleton visualizer" mesh if the file has no mesh data. For others (such
-    as glTF) not.
 -   Per-face attributes in Stanford PLY files are not imported.
 -   Stanford PLY files that contain a comment before the format line fail to
     import.
@@ -302,6 +310,14 @@ verbosity levels in each instance.
 -   The imported model always has either both @ref MeshAttribute::Tangent
     @ref MeshAttribute::Bitangent or neither of them, tangents are always
     three-component with binormals separate.
+-   Joint Ids and weights for skinning are imported as custom vertex attributes
+    named "JOINTS" and "WEIGHTS" with formats @ref VertexFormat::Vector4ui and
+    @ref VertexFormat::Vector4, respectively. Imported meshes always have
+    either both or neither of them. Their mapping to/from a string can be
+    queried using @ref meshAttributeName() and @ref meshAttributeForName().
+    By default, the number of weights per vertex is limited to 4, but you can
+    change this limit by setting the @cb{.ini} maxJointWeights @ce option,
+    see @ref Trade-AssimpImporter-configuration "below".
 -   Multi-mesh nodes and multi-primitive meshes are loaded as follows,
     consistently with the behavior of @link TinyGltfImporter @endlink:
     -   Multi-primitive meshes are split by Assimp into individual meshes
@@ -373,7 +389,10 @@ importer state methods:
     -   @ref LightData::importerState() returns `aiLight`
     -   @ref ImageData2D::importerState() may return `aiTexture`, if texture was embedded
         into the loaded file.
-    -   @ref AnimationData::importerState() returns `aiAnimation`
+    -   @ref AnimationData::importerState() returns `aiAnimation`, or `nullptr` if the
+        @cb{.ini} mergeAnimationClips @ce option is enabled
+    -   @ref SkinData::importerState() returns `aiMesh`, or `nullptr` if the
+        @cb{.ini} mergeSkins @ce option is enabled
 -   @ref openState() expects a pointer to an Assimp scene (i.e., `const aiScene*`)
     and optionally a path (in order to be able to load textures, if needed)
 
@@ -433,7 +452,11 @@ class MAGNUM_ASSIMPIMPORTER_EXPORT AssimpImporter: public AbstractImporter {
         MAGNUM_ASSIMPIMPORTER_LOCAL Containers::Optional<LightData> doLight(UnsignedInt id) override;
 
         MAGNUM_ASSIMPIMPORTER_LOCAL UnsignedInt doMeshCount() const override;
+        MAGNUM_ASSIMPIMPORTER_LOCAL Int doMeshForName(const std::string& name) override;
+        MAGNUM_ASSIMPIMPORTER_LOCAL std::string doMeshName(UnsignedInt id) override;
         MAGNUM_ASSIMPIMPORTER_LOCAL Containers::Optional<MeshData> doMesh(UnsignedInt id, UnsignedInt level) override;
+        MAGNUM_ASSIMPIMPORTER_LOCAL MeshAttribute doMeshAttributeForName(const std::string& name) override;
+        MAGNUM_ASSIMPIMPORTER_LOCAL std::string doMeshAttributeName(UnsignedShort name) override;
 
         MAGNUM_ASSIMPIMPORTER_LOCAL UnsignedInt doMaterialCount() const override;
         MAGNUM_ASSIMPIMPORTER_LOCAL Int doMaterialForName(const std::string& name) override;
@@ -454,6 +477,11 @@ class MAGNUM_ASSIMPIMPORTER_EXPORT AssimpImporter: public AbstractImporter {
         MAGNUM_ASSIMPIMPORTER_LOCAL Int doAnimationForName(const std::string& name) override;
         MAGNUM_ASSIMPIMPORTER_LOCAL Containers::Optional<AnimationData> doAnimation(UnsignedInt id) override;
 
+        MAGNUM_ASSIMPIMPORTER_LOCAL UnsignedInt doSkin3DCount() const override;
+        MAGNUM_ASSIMPIMPORTER_LOCAL Int doSkin3DForName(const std::string& name) override;
+        MAGNUM_ASSIMPIMPORTER_LOCAL std::string doSkin3DName(UnsignedInt id) override;
+        MAGNUM_ASSIMPIMPORTER_LOCAL Containers::Optional<SkinData3D> doSkin3D(UnsignedInt id) override;
+
         MAGNUM_ASSIMPIMPORTER_LOCAL const void* doImporterState() const override;
 
         Containers::Pointer<Assimp::Importer> _importer;