Labels in VPython
VPython (Visual Python) is a 3D graphics library that allows us to create and visualize three-dimensional objects on the screen. It is primarily used to visualize the impact of physics equations on the objects' motion.
Note: Read more about VPython.
Labels
The labels are graphical objects that allow us to display text within a 3D scene. They are used to provide annotations for various objects in the scene.
Syntax
The syntax for adding a label to an object is as follows:
label(pos, text, xoffset, yoffset)
where the parameters are:
pos: It is avectorobject, which sets the position of the label in the scene. We must provide the sameposto the label as its corresponding object.text: We pass the label's display string to thetextparameter.xoffsetandyoffset: These parameters take integer values that move the label in theand directions relative to the passed position vector.
Code execution
To execute the code example provided, follow the steps mentioned in the slides below:
Example code
The following sample code creates a box, cone, and moving sphere in the scene and assigns relevant labels to them. The moving ball's label moves with the sphere.
from vpython import *
import numpy as np
# Create a scene
canvas(width=600, height=600)
# Create the objects
sq = box(size=vector(0.5, 0.01, 0.5), pos=vector(-2, 0.5, 0))
tr = cone(pos=vector(2, 0.2, 0.6), size=vector(0.5, 0.5, 0.5), color=color.yellow)
ball = sphere(radius=0.2, color=color.red, pos=vector(0, -1, 0))
# Create a label
info_label_1 = label(pos=vector(-2, 0.5, 0), text="This is a box object.", xoffset=10, yoffset=20)
info_label_2 = label(pos=vector(2, 0.2, 0.6), text="This is a cone object.", xoffset=10, yoffset=20)
annotation = label(pos=vector(0, ball.pos.y, 0), text="Moving Ball", xoffset=20, yoffset=20)
i = 2
direction = 1 # 1 for increasing, -1 for decreasing
while True:
rate(100) # Reduce the animation rate
ball.pos.y = 1 - i
ball.pos = vector(0, ball.pos.y, 0)
annotation.pos = vector(0, ball.pos.y, 0) # Update the annotation position
if direction == 1:
i += 0.005
if i >= 4:
direction = -1
else:
i -= 0.005
if i <= 2:
direction = 1Code explanation
Lines 1–2: Importing the necessary library.
Line 5: Creating a window for the scene.
Lines 8–10: Three objects (
box,coneandsphere) are created. Out of these three objects, only the sphere moves back and forth.Lines 13–15: Assigning the labels to the relevant objects.
Note: The labels have same
posvectors as their corresponding objects.
Line 17–18:
iis an iterator in the loop below. Thedirectionis positive if the ball moves upwards and negative if it goes downwards.Line 21: The
rate()specifies the frames per second of the animation.Lines 22–24: Repeatedly update the sphere's position and label.
Lines 26–33: Changing the sphere's direction.
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