Miêu Tả Cảnh Phổ Thông (Universal Scene Description)

Xuất Ra Tập Tin USD (Exporting to USD Files)

Universal Scene Description (USD) files can contain complex layering, overriding, and references to other files. Blender's USD Exporter takes a much simpler approach. When exporting, all visible, supported objects in the scene are exported, optionally limited by their selection state. Blender does not (yet) support exporting invisible objects, USD layers, variants, skeletal animation, etc.

Những kiểu dữ liệu hỗ trợ bao gồm:

  • Meshes (of different kinds, see below).

  • Cameras (perspective cameras only at the moment, not orthogonal ones).

  • Light (all types except area lights).

  • Hair (exported as curves, and limited to parent strands).

  • Volume (both static and animated volumes).

When exporting an animation, the final, evaluated mesh is written to USD. This means that the following meshes can be exported:

  • Static meshes.

  • Deforming meshes; here the topology of the mesh does not change, but the locations of the vertices change over time. Examples are animated characters or bouncing (but not cracking) objects.

  • Arbitrarily animated meshes; here the topology does change. An example is the result of a fluid simulation, where splashes of fluid can break off the main body.

  • Metaballs are exported as animated meshes.

../../_images/files_import-export_usd_example.png

Shot from Spring exported to USD and opened in USDView.

Các Tùy Chọn về Xuất Khẩu (Export Options)

The following options are available when exporting to USD:

Duy Lựa Chọn (Selection Only)

When checked, only selected objects are exported. Instanced objects, for example collections that are instanced in the scene, are considered 'selected' when their instancer is selected.

Duy Hữu Hình (Visible Only)

Only exports objects that are not hidden. Invisible parents of exported objects are exported as empty transforms.

Animation (Hoạt Họa)

When checked, the entire scene frame range is exported. When unchecked, only the current scene frame is exported.

Tóc/Lông (Hair)

When checked, parent hair strands are exported as a curve system. Hair strand colors are not exported.

Ánh Xạ UV (UV Maps)

When checked, includes UV coordinates for exported meshes. The name of the UV map in USD is the same as the name in Blender. In USD the default name is st whereas in Blender the default name is UVMap. To export to the standard UV map name st, rename the UV map in Blender to st.

Pháp Tuyến (Normals)

When checked, includes normals for exported meshes. This includes custom loop normals.

Nguyên Vật Liệu (Materials)

Exports material information of the object. By default the exporter approximates the BSDF Nguyên Tắc (Principled BSDF) node tree by converting it to USD's Preview Surface format. If To USD Preview Surface is disabled, the material is set to the viewport materials of meshes.

Additional material properties are set in the Material grouping of options.

When a mesh has multiple materials assigned, a geometry subset is created for each material. The first material (if any) is always applied to the mesh itself as well (regardless of the existence of geometry subsets), because the Hydra viewport does not support materials on subsets. See USD issue #542 for more information.

Sử Dụng các sắp đặt cho (Use Settings for)

Determines the whether to use Viewport or Render visibility of collection, modifiers, or any other property that can be set for both the Viewport and Render.

Nguyên Vật Liệu (Materials)

Additional options when Materials are enabled for export.

Thành Bề Mặt Duyệt Thảo USD (To USD Preview Surface)

When exporting materials, approximate a BSDF Nguyên Tắc (Principled BSDF) node tree to by converting it to USD's Preview Surface format. If disabled, the material is set to the viewport materials of meshes.

Cảnh báo

Not all nodes are supported; currently only Diffuse, Principle, Image Textures, and UVMap nodes are support.

Xuất Khẩu Chất Liệu (Export Textures)

Export textures referenced by shader nodes to a "textures" folder which in the same directory as the USD file.

Viết Đè Chất Liệu (Overwrite Textures)

Cho phép viết đè lên các tập tin chất liệu hiện có khi xuất khẩu chất liệu.

Tham Chiếu Tập Tin (File References)

Đường Dẫn Tương Đối (Relative Paths)

Use relative paths to reference external files (i.e. textures, volumes) in the exported USD file, otherwise use absolute paths.

Thử Nghiệm (Experimental)

Thực Thể Hóa (Instancing)

As this is an experimental option. When unchecked, duplicated objects are exported as real objects, so a particle system with 100 particles that is displayed with 100 meshes will have 100 individual meshes in the exported file. When checked, duplicated objects are exported as a reference to the original object. If the original object is not part of the export, the first duplicate is exported as real object and used as reference.

Những Giới Hạn của Trình Xuất Khẩu (Exporter Limitations)

Khung Lưới Một Mặt Bên và Hai Mặt (Single-sided and Double-sided Meshes)

USD seems to support neither per-material nor per-face-group double-sidedness, so Blender uses the flag from the first material to mark the entire mesh as single/double-sided. If there is no material it defaults to double-sided.

Các Pháp Tuyến của Khung Lưới (Mesh Normals)

The mesh subdivision scheme in USD is 'Catmull-Clark' by default, but Blender uses 'None' instead, indicating that a polygonal mesh is exported. This is necessary for USD to understand the custom normals; otherwise the mesh is always rendered smooth.

Tốc Lực của Điểm Đỉnh (Vertex Velocities)

Currently only fluid simulations (not meshes in general) have explicit vertex velocities. This is the most important case for exporting velocities, though, as the baked mesh changes topology all the time, and thus computing the velocities at import time in a post-processing step is hard.

Định Hướng của Hệ Thống Tọa Độ (Coordinate System Orientation)

Blender uses the Z axis as up axis. Since USD supports both Y up and Z up, the USD files written by Blender always use Z up.

Nguyên Vật Liệu (Materials)

Very simple versions of the materials are exported, using only the Hiển Thị Cổng Nhìn (Viewport Display) color, metallic, and roughness.

When there are multiple materials, the mesh faces are stored as geometry subset and each material is assigned to the appropriate subset. If there is only one material this is skipped. Note that the geometry subsets are not time-sampled, so it may break when an animated mesh changes topology.

Tóc/Lông (Hair)

Only the parent strands are exported, and only with a constant color. No UV coordinates, and no information about the normals.

Máy Quay Phim (Camera)

Only perspective cameras are exported.

Nguồn Ánh Sáng (Lights)

USD does not directly support spot lights, so those are not exported.

Hạt (Particles)

Particles are only written when they are alive, which means that they are always visible. There is currently no code that deals with marking them as invisible outside their lifespan.

Objects instanced by particle system are exported by suffixing the object name with the particle's persistent ID, giving each particle transform a unique name.

Thực Thể Hóa/Tham Chiếu Hóa (Instancing/Referencing)

This is still an experimental feature that can be enabled when exporting to USD. When enabled, instanced object meshes are written to USD as references to the original mesh. The first copy of the mesh is written for real, and the following copies are referencing the first. Which mesh is considered 'the first' is chosen more or less arbitrarily.

Nhập Khẩu Tập Tin POV-Ray (Importing USD Files)

USD files typically represent the scene as a hierarchy of primitives, or prims. Individual prims contain data to describe scene entities, such as geometry, lights, cameras and transform hierarchies. Blender's USD importer converts USD prims to a hierarchy of Blender objects. Like the USD exporter, the importer does not yet handle more advanced USD concepts, such as layers and references.

Những kiểu dữ liệu hỗ trợ bao gồm:

  • Máy Quay Phim (Cameras)

  • Đường Cong (Curves)

  • Nguồn Ánh Sáng (Lights)

  • Nguyên Vật Liệu (Materials)

  • Khung Lưới (Meshes)

  • Âm Lượng/Thể Tích (Volume)

For more information on how the various data types are handled, see the following descriptions of the Import Options.

Hình Học Cơ Bản Nền Tảng Macro (Xform and Scope Primitives)

USD provides an Xform prim type, containing transform data, which can be used to represent transform hierarchies and to organize the scene. Such Xform prims are imported as Blender empty objects.

USD also supports Scope primitives, which are entities that do not contain transform data, but which serve to group other element of the scene. Blender doesn't have an exact counterpart to the concept of a scope, so such primitives are imported as Blender empties located at the origin. This is an imperfect representation, because empty objects have a transform and Scopes do not, but this approach nonetheless helps preserve the structure of the scene hierarchy.

Hoạt Họa (Animations)

The importer supports two types of animation:

  • Animating transforms: If a USD primitive has time-varying transform data, a Transform Cache constraint will be added to the imported Blender object.

  • Animating geometry: Animating mesh and curve geometry is supported by adding a Mesh Sequence Cache modifier to the imported data. Geometry attribute (USD Primvar) animation is currently supported only for Color Attributes and UVs. Note that USD file sequences (i.e. a unique file per frame) are not yet supported.

Nguyên Vật Liệu (Materials)

If a USD mesh or geometry subset has a bound material, the importer will assign to the Blender object a material with the same name as the USD material. If a Blender material with the same name already exists in the scene, the existing material will be assigned. Otherwise, a new material will be created.

If the USD material has a USD Preview Surface shader source, the Hiển Thị Cổng Nhìn (Viewport Display) color, metallic, and roughness are set to the corresponding USD Preview Surface input values.

There is also an experimental Import USD Preview option to convert USD Preview Surface shaders to Blender Principled BSDF shader nodes. This option can be lossy, as it does not yet handle converting all shader settings and types, but it can generate approximate visualizations of the materials.

Định Hướng của Hệ Thống Tọa Độ (Coordinate System Orientation)

If the imported USD is Y up, a rotation will be automatically applied to root objects to convert to Blender's Z up orientation.

Tùy Chọn Nhập Khẩu (Import Options)

The following options are available when importing from USD:

Máy Quay Phim (Cameras)

Chuyển đổi giữa chế độ góc nhìn phối cảnh xa gần và chế độ góc nhìn trực giao.

Đường Cong (Curves)

Import curve primitives, including USD basis and NURBS curves. (Note that support for Bézier basis is not yet fully implemented.)

Nguồn Ánh Sáng (Lights)

Import lights. Does not currently include USD dome, cylinder or geometry lights.

Nguyên Vật Liệu (Materials)

Import materials. See also the experimental Import USD Preview option.

Khung Lưới (Meshes)

Nhập Khẩu Bảng Pha Màu.

Thể Tích (Volumes)

Import USD OpenVDB field assets.

Chắn Lọc Đường Dẫn (Path Mask)

Chỉ nhập tập hợp con (subset) của cảnh USD, tức cái bắt nguồn từ đối tượng cơ bản nhất định nào đó.

Tỷ Lệ (Scale)

Value by which to scale the imported objects in relation to the world's origin.

Tọa Độ UV (UV Coordinates)

Đọc tọa độ UV của khung lưới.

Thuộc Tính Màu (Color Attributes)

Convert the USD mesh displayColor values to Blender's Color Attributes.

Phân Hóa (Subdivision)

Create Subdivision Surface modifiers based on the USD SubdivisionScheme attribute.

Nhập Khẩu Thực Thể Đại Diện (Import Instance Proxies)

Biến các thực thể USD thành các đối tượng Blender độc đáo/duy nhất.

Duy Đối Tượng Cơ Bản Nhìn Thấy Được (Visible Primitives Only)

Do not import invisible USD primitives. Only applies to primitives with a non-animated visibility attribute. Primitives with animated visibility will always be imported.

Hướng Dẫn (Guide)

Include primitives with purpose guide.

Proxy (Đại Diện)

Include primitives with purpose proxy.

Render (Kết Xuất)

Include primitives with purpose render.

Đặt Phạm Vi Khung Hình (Set Frame Range)

Cập nhật khung hình khởi đầu và kết thúc của cảnh để khớp với những khung hình của kho lưu trữ USD

Đường Dẫn Tương Đối (Relative Path)

Select the file relative to the blend-file.

Tạo Tập Hợp (Create Collection)

Thêm toàn bộ các đối tượng đã nhập vào tập hợp mới.

Tỷ Lệ Cường Độ Ánh Sáng (Light Intensity Scale)

Tỷ lệ cho cường độ ánh sáng của các nguồn sáng nhập khẩu.

Tên nguyên Vật Liệu Xung Đột (Material Name Collision)

Phương pháp hành xử khi tên của nguyên vật liệu nhập khẩu xung đột với nguyên vật liệu hiện có.

Biến Thành Độc Nhất (Make Unique)

Nhập từng nguyên vật liệu USD làm nguyên vật liệu Blender độc nhất.

Tham Chiếu cái hiện Tồn Tại (Reference Existing)

Nếu một nguyên vật liệu có cùng tên đã tồn tại rồi thì hãy tham chiếu đến nguyên vật liệu đó thay vì nhập khẩu.

Thử Nghiệm (Experimental)

Nhập Khẩu Duyệt Thảo USD (Import USD Preview)

Convert USD Preview Surface shaders to Principled BSDF shader networks.

Bật tính năng Pha Trộn nguyên Vật Liệu (Set Material Blend)

If the Import USD Preview option is enabled, the material blend method will automatically be set based on the opacity and opacityThreshold shader inputs, allowing for visualization of transparent objects.