FreeStyle API Change for Blender 2.70

Tamito Kajiyama with the help of developers in the Blender community, proposed a revision to Freestyle API to make it more usable. Here is what he wrote.


In the upcoming Blender 2.70 release, a revision of the Freestyle Python API is planned in a backward incompatible manner (D163). The basic idea is to reorganize Freestyle-related Python modules in line with the bpy module and its submodules, now that some breakage of backwards compatibility is allowed with the 2.7x series. The proposed changes aim to address the following issues observed in the present Freestyle implementation:

  1. Freestyle API constructs for style module writing in Python are not logically organized. The API modules are partly organized in terms of implementation languages (C and Python) and partly based on implemented roles (predicates, chaining iterators, and so on).
  2. All Python scripts for Freestyle, i.e., both API modules and application programs (style modules), are stored in the same ‘release/scripts/freestyle/style_modules’ directory. This makes it difficult for new users to find style modules.

New Python module organization

The new Python module directory structure is proposed as follows:

  • release/scripts/freestyle/modules – Freestyle API modules
  • release/scripts/freestyle/styles – predefined style modules

In Python, the Freestyle API modules are reorganized as follows:

  • freestyle – top-level package just containing the following submodules.
  • freestyle.types – classes for core data structures, and base classes for user-defined stylization rules (i.e., chaining iterators, predicates, functions, and shaders).
  • freestyle.chainingiterators – predefined chaining iterators.
  • freestyle.predicates – predefined 0D and 1D predicates.
  • freestyle.functions – predefined 0D and 1D functions.
  • freestyle.shaders – predefined stroke shaders.
  • freestyle.utils – utility functions for style module writing.

Code examples before/after the API revision

The effects of the proposed changes are illustrated below by taking the style module as example. With the present API organization (before the proposed changes), the import statements in the beginning of the style module have been written as follows:

from freestyle import BezierCurveShader, ChainSilhouetteIterator, ConstantColorShader, \
    ConstantThicknessShader, IntegrationType, Operators, QuantitativeInvisibilityUP1D, \
    SamplingShader, TextureAssignerShader, TipRemoverShader
from Functions0D import pyInverseCurvature2DAngleF0D
from PredicatesB1D import pyLengthBP1D
from PredicatesU0D import pyParameterUP0D
from PredicatesU1D import pyDensityUP1D, pyHigherLengthUP1D, pyHigherNumberOfTurnsUP1D
from logical_operators import NotUP1D
from shaders import pyNonLinearVaryingThicknessShader, pySamplingShader

With the proposed API changes, these import statements will be written as follows:

from freestyle.chainingiterators import ChainSilhouetteIterator
from freestyle.functions import pyInverseCurvature2DAngleF0D
from freestyle.predicates import (
from freestyle.shaders import (
from freestyle.types import IntegrationType, Operators

From the applicative perspective, the new organization will be much easier for style module writers to find relevant Python constructs from the freestyle.* submodules. It is remarked that there is no functional difference (no visual effects in rendering results) between the present and new module organizations.


Many thanks to flokkievids (Folkert Vries) for careful discussions, code review and patches through the task T37565.

TL;DR: The idea is to re-organize Python packages so that elements for style module writing are better organized by logical roles rather than the way how they are implemented. There is no functionality change — the only changes are the way how style module writers would specify ‘import’ statements in the beginning of Python style modules. For artist-type users, the API revision does not have any visual effects.

We here at BNPR welcome this revision, it is now easier to see the logical roles of modules, and we might see coder-artists get their hands dirty coding awesome line arts.

Source: FreeStyle API Reorganization

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