Moving on to 3D elements

After the first evaluations, my mentors and I have decided to put a hold on the 2D elements and move to creating 3D UIs and widgets.


Apart from continuously fixing bugs in my previous contributions, I have created a new element, which is a file select menu that allows the user to browse their file system and look at files and folders. They can navigate into and out of directories by clicking on them in the menu.

This element uses the ListBox2D I talked about in my previous post. Files are shown with Blue color and directories with Green.

The PR for this can be found here.

Orbital Menu

The first 3D element that I am creating is an orbital menu. A basic version of this was designed by my mentor 2 years ago.

The main challenge here is to ensure that the menu(disk here) around the object(cubes here) follows the camera always so that they can always be visible. For this, the vtkFollower class is used.

My task here is to first adapt the old version of the code to work with the current codebase. Then, I have to discuss various ideas to make this menu user-friendly and sci-fi and implement them.

Experimenting with Assemblies

Assemblies are a very important part of 3D graphics as they allow us to create a hierarchical model of the elements in a scene. Imagine a 3D model of a human arm. There is a three-level hierarchy – the arm, then the hand and finally the fingers. Any transformation on a parent element in the hierarchy must be applied to the children, while allowing the children to have their own independent motion about their parent.

Thus, if a hand moves, the same motion applies to the fingers. Additionally, the fingers have their local transformations with respect to the knuckles. Assemblies help us in achieving this hierarchy.

in vtk, the vtkAssemblyclass create hierarchies of elements. Parts can be added using the AddPart member function.

I have been experimenting with this a lot to fully understand how assemblies work and wrote a small code to create a 3-level hierarchy of 3 cubes.

import dipy.viz.ui as ui
import dipy.viz.window as window

Cube actor

def cube_maker(color=None, size=(0.2, 0.2, 0.2), center=None):
     cube = window.vtk.vtkCubeSource()
     if center is not None:
     cube_mapper = window.vtk.vtkPolyDataMapper()
     cube_actor = window.vtk.vtkActor()
     if color is not None:
     return cube_actor

cube_actor_1 = cube_maker((1, 0, 0), (25, 25, 25), center=(0, 0, 0))
cube_actor_2 = cube_maker((0, 1, 0), (10, 10, 10), center=(50, 0, 0))
cube_actor_3 = cube_maker((0, 0, 1), (5, 5, 5), center=(100, 0, 0))

Creating assembly

assembly1 = window.vtk.vtkAssembly()
assembly2 = window.vtk.vtkAssembly()



Adding sliders to transform the cubes

def translate_blue_cube(slider):
     value = slider.value
     cube_actor_3.SetPosition(value, 0, 0)

def translate_green_cube(slider):
     value = slider.value
     assembly2.SetPosition(value, 0, 0)

def translate_red_cube(slider):
     value = slider.value
     assembly1.SetPosition(value, 0, 0)

def rotate_blue_cube(slider):
     angle = slider.value
     previous_angle = slider.previous_value
     rotation_angle = angle - previous_angle

def rotate_green_cube(slider):
     angle = slider.value
     previous_angle = slider.previous_value
     rotation_angle = angle - previous_angle

def rotate_red_cube(slider):
     angle = slider.value
     previous_angle = slider.previous_value
     rotation_angle = angle - previous_angle

ring_slider1 = ui.RingSlider2D(text_template="{angle:5.1f}°", center = (100, 500))
ring_slider1.on_change = rotate_red_cube

ring_slider2 = ui.RingSlider2D(text_template="{angle:5.1f}°", center = (300, 500))
ring_slider2.on_change = rotate_green_cube

ring_slider3 = ui.RingSlider2D(text_template="{angle:5.1f}°", center = (500, 500))
ring_slider3.on_change = rotate_blue_cube

line_slider1 = ui.LineSlider2D(center=(100, 100), initial_value=0, min_value=-10, max_value=10, length=150)
line_slider1.on_change = translate_red_cube

line_slider2 = ui.LineSlider2D(center=(300, 100), initial_value=0, min_value=-10, max_value=10, length=150)
line_slider2.on_change = translate_green_cube

line_slider3 = ui.LineSlider2D(center=(500, 100), initial_value=0, min_value=-10, max_value=10, length=150)
line_slider3.on_change = translate_blue_cube

Adding Elements to the ShowManager

Once all elements have been initialised, they have
to be added to the show manager in the following manner.

current_size = (600, 600)
show_manager = window.ShowManager(size=current_size)

I use the “Peek” screen recorder on Ubuntu to record these demos.

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