Visualizing with Blender

The basics

There are two functions in the library to visualize objects in Blender. convert() is intended to work for almost all objects you can create with the library like spheres, quadrics and subspaces. vertices() provides additional options to visualize points.

As an example we create a quadric (ellipsoid).

>>> import numpy as np
>>> import ddg
>>> ellipsoid = ddg.geometry.Quadric(np.diag([1 / 2, 1, 1, -1]))
>>> bobj = ddg.blender.convert(ellipsoid, "Ellipsoid")

You should get something looking like this:

You can also visualize subspaces:

>>> line = ddg.geometry.subspace_from_affine_points([1, 0, 0], [0, 1, 0])
>>> bobj = ddg.blender.convert(line, "Line")

The API documentation for convert() contains an exhaustive list of examples.

Names

You always need to set a name for the object to visualize. This name must be unique, otherwise you will get errors.

If you need to create multiple objects in a loop, use enumerate to add an index. Here we create multiple circles in the form of a conics with different radii.

>>> euc_2 = ddg.geometry.euclidean(2)
>>> list_of_circles = [euc_2.sphere((0, 0, 1), r) for r in range(1, 4)]
>>> for i, circle in enumerate(list_of_circles):
...     bobj = ddg.blender.convert(circle, f"circle {i}")
...

Blender objects, curves and meshes

convert() always returns a Blender object or more precisely, a bpy.types.Object. It has attributes that you can change after it was created. For example

>>> bobj.hide_viewport = True

will make the line vanish from the viewport and it will reappear after

>>> bobj.hide_viewport = False

Every Blender object has a data attribute. Most of the time, this is a Blender curve of type bpy.types.Curve for 1-dimensional objects, or a Blender mesh of type bpy.types.Mesh for 2-dimensional objects. They also have interesting attributes. For example, for a curve you can change its bevel_depth which is its thickness.

>>> bobj.data.bevel_depth = 0.1

For more information, refer to Blender’s documentation:

• Blender Object API

• Blender Curve API

• Blender Mesh API

Scattering points and edges

You can use convert() to visualize points or 0-dimensional subspaces, but it is recommended to use vertices(), where you can change how the points are to be visualized.

>>> point = ddg.arrays.Points([0, 1, 1])
>>> bobj = ddg.blender.vertices(point, "Point", radius=0.1)

See the documentation for more details vertices(). The function scatter() allows to put arbitrary meshes at each vertex position. Similarly, if you wish to only visualize the edges of a mesh, use edges().

Visualizing SmoothNet and SmoothCurve

By design convert() cannot visualize ddg.nets.SmoothNet and ddg.nets.SmoothCurve. The sampling section of the nets documentation describes how to obtain a ddg.nets.DiscreteNet or ddg.nets.DiscreteCurve from a smooth net or curve. These can be visualized directly with convert().

Customizing visualization

By design convert() provides reasonable defaults to convert every pyddg object except for ddg.nets.SmoothNet and ddg.geometry.SmoothCurve. For example, it samples smooth objects such as quadrics with reasonably high quality and embeds pyddg objects in R^2 into the xy-plane of R^3.

>>> ellipsoid = ddg.geometry.Quadric(np.diag([1 / 2, 1, 1, -1]))
>>> sampled_ellipsoid = ddg.arrays.from_quadric(ellipsoid, (10, 0.1), (10, 0.1))
>>> bobj = ddg.blender.convert(sampled_ellipsoid, "Sampled Ellipsoid")

The module ddg.arrays contains similar functions every pyddg object other than ddg.nets.SmoothNet an ddg.nets.SmoothCurve, e.g.

• from_quadric() for manual sampling

• from_quadric_sphere() for manual sampling

• from_indexed_face_set() to choose a coordinate attribute other than co

• from_half_edge_surface() to choose a coordinate attribute other than co

• from_1d_subspace() to create long line segments from a ddg.geometry.Subspace

• from_2d_subspace() to create large rectangles from a ddg.geometry.Subspace

• line_segment_from_points() to create a line segment

• line_segment_from_point_and_direction() to create a line segment

See also

• convert()

• vertices()

• scatter()

• edges()

• line_segment_from_points()

• line_segment_from_point_and_direction()

• Mesh()

• Curve()

• Points()

• arrays()