Commit: dd3a72f275b3dfed3c6529d7ede48875149dc186 Author: Hans Goudey Date: Sat Dec 25 15:08:38 2021 -0600 Branches: master https://developer.blender.org/rBdd3a72f275b3dfed3c6529d7ede48875149dc186
Docs: Add to and cleanup attribute API docs Most of the comment block is similar to the text in the source code documentation wiki. It's helpful to have some text in a header file too, so it's closer for programmers already looking at the code. This also uses more consistent syntax and wording in the comments about the attribute API in `GeometryComponent`. Ref T93753 Differential Revision: https://developer.blender.org/D13661 =================================================================== M source/blender/blenkernel/BKE_attribute_access.hh M source/blender/blenkernel/BKE_geometry_set.hh =================================================================== diff --git a/source/blender/blenkernel/BKE_attribute_access.hh b/source/blender/blenkernel/BKE_attribute_access.hh index ae9969aae82..114d9e1e0d7 100644 --- a/source/blender/blenkernel/BKE_attribute_access.hh +++ b/source/blender/blenkernel/BKE_attribute_access.hh @@ -30,6 +30,39 @@ #include "BLI_float3.hh" #include "BLI_function_ref.hh" +/** + * This file defines classes that help to provide access to attribute data on a #GeometryComponent. + * The API for retrieving attributes is defined in `BKE_geometry_set.hh`, but this comment has some + * general comments about the system. + * + * Attributes are stored in geometry data, though they can also be stored in instances. Their + * storage is often tied to `CustomData`, which is a system to store "layers" of data with specific + * types and names. However, since `CustomData` was added to Blender before attributes were + * conceptualized, it combines the "legacy" style of task-specific attribute types with generic + * types like "Float". The attribute API here only provides access to generic types. + * + * Attributes are retrieved from geometry components by providing an "id" (#AttributeIDRef). This + * is most commonly just an attribute name. The attribute API on geometry components has some more + * advanced capabilities: + * 1. Read-only access: With a `const` geometry component, an attribute on the geometry cannot be + * modified, so the `for_write` and `for_output` versions of the API are not available. This is + * extremely important for writing coherent bug-free code. When an attribute is retrieved with + * write access, via #WriteAttributeLookup or #OutputAttribute, the geometry component must be + * tagged to clear caches that depend on the changed data. + * 2. Domain interpolation: When retrieving an attribute, a domain (#AttributeDomain) can be + * provided. If the attribute is stored on a different domain and conversion is possible, a + * version of the data interpolated to the requested domain will be provided. These conversions + * are implemented in each #GeometryComponent by `attribute_try_adapt_domain_impl`. + * 3. Implicit type conversion: In addition to interpolating domains, attribute types can be + * converted, using the conversions in `BKE_type_conversions.hh`. The #VArray / #GVArray system + * makes it possible to only convert necessary indices on-demand. + * 4. Anonymous attributes: The "id" used to look up an attribute can also be an anonymous + * attribute reference. Currently anonymous attributes are only used in geometry nodes. + * 5. Abstracted storage: Since the data returned from the API is usually a virtual array, + * it doesn't have to be stored contiguously (even though that is generally preferred). This + * allows accessing "legacy" attributes like `material_index`, which is stored in `MPoly`. + */ + namespace blender::bke { /** diff --git a/source/blender/blenkernel/BKE_geometry_set.hh b/source/blender/blenkernel/BKE_geometry_set.hh index 79f29e0954e..834d943d9ce 100644 --- a/source/blender/blenkernel/BKE_geometry_set.hh +++ b/source/blender/blenkernel/BKE_geometry_set.hh @@ -93,41 +93,64 @@ class GeometryComponent { GeometryComponentType type() const; - /* Return true when any attribute with this name exists, including built in attributes. */ + /** + * Return true when any attribute with this name exists, including built in attributes. + */ bool attribute_exists(const blender::bke::AttributeIDRef &attribute_id) const; - /* Return the data type and domain of an attribute with the given name if it exists. */ + /** + * Return the data type and domain of an attribute with the given name if it exists. + */ std::optional<AttributeMetaData> attribute_get_meta_data( const blender::bke::AttributeIDRef &attribute_id) const; - /* Returns true when the geometry component supports this attribute domain. */ + /** + * Return true when the geometry component supports this attribute domain. + * \note Conceptually this function is static, the result is always the same for different + * instances of the same geometry component type. + */ bool attribute_domain_supported(const AttributeDomain domain) const; - /* Can only be used with supported domain types. */ + /** + * Return the length of a specific domain, or 0 if the domain is not supported. + */ virtual int attribute_domain_size(const AttributeDomain domain) const; + /** + * Return true if the attribute name corresponds to a built-in attribute with a hardcoded domain + * and data type. + */ bool attribute_is_builtin(const blender::StringRef attribute_name) const; bool attribute_is_builtin(const blender::bke::AttributeIDRef &attribute_id) const; - /* Get read-only access to the highest priority attribute with the given name. - * Returns null if the attribute does not exist. */ + /** + * Get read-only access to an attribute with the given name or id, on the highest priority domain + * if there is a name collision. + * \return null if the attribute does not exist. + */ blender::bke::ReadAttributeLookup attribute_try_get_for_read( const blender::bke::AttributeIDRef &attribute_id) const; - /* Get read and write access to the highest priority attribute with the given name. - * Returns null if the attribute does not exist. */ + /** + * Get read and write access to an attribute with the given name or id, on the highest priority + * domain if there is a name collision. + * \note #WriteAttributeLookup.tag_modified_fn must be called after modifying data. + * \return null if the attribute does not exist + */ blender::bke::WriteAttributeLookup attribute_try_get_for_write( const blender::bke::AttributeIDRef &attribute_id); - /* Get a read-only attribute for the domain based on the given attribute. This can be used to + /** + * Get a read-only attribute for the domain based on the given attribute. This can be used to * interpolate from one domain to another. - * Returns null if the interpolation is not implemented. */ + * \return null if the interpolation is not implemented. + */ blender::fn::GVArray attribute_try_adapt_domain(const blender::fn::GVArray &varray, const AttributeDomain from_domain, const AttributeDomain to_domain) const { return this->attribute_try_adapt_domain_impl(varray, from_domain, to_domain); } - + /* Use instead of the method above when the type is known at compile time for type safety. */ template<typename T> blender::VArray<T> attribute_try_adapt_domain(const blender::VArray<T> &varray, const AttributeDomain from_domain, @@ -137,17 +160,19 @@ class GeometryComponent { .template typed<T>(); } - /* Returns true when the attribute has been deleted. */ + /** Returns true when the attribute has been deleted. */ bool attribute_try_delete(const blender::bke::AttributeIDRef &attribute_id); - /* Returns true when the attribute has been created. */ + /** Returns true when the attribute has been created. */ bool attribute_try_create(const blender::bke::AttributeIDRef &attribute_id, const AttributeDomain domain, const CustomDataType data_type, const AttributeInit &initializer); - /* Try to create the builtin attribute with the given name. No data type or domain has to be - * provided, because those are fixed for builtin attributes. */ + /** + * Try to create the builtin attribute with the given name. No data type or domain has to be + * provided, because those are fixed for builtin attributes. + */ bool attribute_try_create_builtin(const blender::StringRef attribute_name, const AttributeInit &initializer); @@ -160,34 +185,41 @@ class GeometryComponent { virtual bool is_empty() const; - /* Get a virtual array to read the data of an attribute on the given domain and data type. - * Returns null when the attribute does not exist or cannot be converted to the requested domain - * and data type. */ + /** + * Get a virtual array that refers to the data of an attribute, interpolated to the given domain + * and converted to the data type. Returns null when the attribute does not exist or cannot be + * interpolated or converted. + */ blender::fn::GVArray attribute_try_get_for_read(const blender::bke::AttributeIDRef &attribute_id, const AttributeDomain domain, const CustomDataType data_type) const; - /* Get a virtual array to read the data of an attribute on the given domain. The data type is - * left unchanged. Returns null when the attribute does not exist or cannot be adapted to the - * requested domain. */ + /** + * Get a virtual array that refers to the data of an attribute, interpolated to the given domain. + * The data type is left unchanged. Returns null when the attribute does not exist or cannot be + * interpolated. + */ blender::fn::GVArray attribute_try_get_for_read(const blender::bke::AttributeIDRef &attribute_id, const AttributeDomain domain) const; - /* Get a virtual array to read data of an attribute with the given data type. The domain is - * left unchanged. Returns null when the attribute does not exist or cannot be converted to the - * requested data type. */ + /** + * Get a virtual array that refers to the data of an attribute converted to the given data type. + * The attribute's domain is left unchanged. Returns null when the attribute does not exist or + * cannot be converted. + */ blender::bke::ReadAttributeLookup attribute_try_get_for_read( const blender::bke::AttributeIDRef &attribute_id, const CustomDataType data_type) const; - /* Get a virtual array to read the data of an attribute. If that is not possible, the returned - * virtual array will contain a default value. This never @@ Diff output truncated at 10240 characters. @@ _______________________________________________ Bf-blender-cvs mailing list [email protected] List details, subscription details or unsubscribe: https://lists.blender.org/mailman/listinfo/bf-blender-cvs
