Introduction to Python PyOpenGL

In this tutorial, we’ll learn about the PyOpenGL library in Python and how to use it. OpenGL is an open-source library that supports multiple platforms, including Windows, Linux, and macOS. It’s also supported by several programming languages. We will implement this using the Python programming language.

Introduction

OpenGL is a relatively simple library that’s easier to implement than other graphics libraries. It’s a cross-language API, so it can be used in other programming languages. In OpenGL, we need to specify objects in space. For example, to create a cube, we need to specify its corners. Corners are called vertices (plural) or vertices (singular).

Installation

We can easily install it using the pip package manager. Run the following command in your terminal to install OpenGL on your system.

pip install pyopengl pyopengl_accelerate

The above command will install PyOpenGL in your local system. You will get the following output.

You can manually download it by following the steps below:

1. Go to the specified link and scroll down to the “Download and Install” heading.
2. Download all necessary files from that section.
3. Navigate to the folder where you downloaded the files.
4. Run the appropriate command in the terminal or command prompt to install or execute the file.
   python setup.py

This command will install the files and set up the necessary environment for the program to run.

Note that the above command assumes that Python and the setup tools are installed on your system and that the setup.py file is located in the same folder as the one your terminal or command prompt is open to.

Now, let’s move on to implementation by coding.

Implementation

The first step is to import OpenGL into your code. To do this, run the following command.

import OpenGL

Before continuing, we must import some additional dependencies in order to use this library in our program. These dependencies should be installed before attempting to use the library in our program. Here are some libraries:

import OpenGL.GL
import OpenGL.GLUT
import OpenGL.GLU
print("Imports successful!")

When we run the code snippet above, we get “Imports successful,” which means we’ve successfully installed the libraries.

Now, let’s create a window to display graphics using the OpenGL library. The following code creates a window, and the comments explain how it works.

Example –

from OpenGL.GLUT import *
from OpenGL.GL import *
from OpenGL.GLU import *

def showScreen():
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT) # Clear the screen and reset the color and depth buffers

# Initialize the GLUT instance that allows us to customize the window
glutInit()
# Set the display mode to use RGB colors
glutInitDisplayMode(GLUT_RGBA)
# Set the width and height of the window
glutInitWindowSize(500, 500)
# Set the window's position on the screen
glutInitWindowPosition(0, 0)
# Give the window a title
wind = glutCreateWindow("OpenGL Graphics Window") glutDisplayFunc(showScreen) # Tell GLUT Call the showScreen function to continuously update the window.
glutIdleFunc(showScreen) # Draw any graphics or shapes in the showScreen function.
glutMainLoop() # Keep the window created above displayed/running in a loop.

Description –
In the above code, we create a window titled “OpenGL Graphics Window,” with a size of 500×500 pixels and positioned in the upper-left corner of the screen. The glutDisplayFunc() and glutIdleFunc() methods continuously call the showScreen() function. This function is responsible for clearing the screen and displaying any graphics or shapes. The glutMainLoop() function is responsible for keeping the window open and updating its contents. Note that the above code uses the Python OpenGL bindings; if you’re using another programming language, you might use a different library.

Now, we’ll create a square using OpenGL, but we should be familiar with the coordinate system OpenGL follows—

The point (0,0) in the window represents the lower-left corner of the window. If we move upward from this point, we traverse along the y-axis, and if we move right from this point, we traverse along the x-axis. Therefore, the upper-left corner of the window will be (0,500), the upper-right corner will be (500,500), and the lower-right corner will be (500,0).

It’s worth noting that the y-axis increases as we move upward, while the x-axis increases as we move right, which is the opposite of the traditional Cartesian coordinate system.

Let’s write the code to create a square.

Code Example

from OpenGL.GL import *
from OpenGL.GLUT import *
from OpenGL.GLU import *

# Define coordinates
w, h = 500, 500

# Function to create a square
def square():
glBegin(GL_QUADS) # Start drawing
glVertex2f(100, 100) # Coordinates of the lower left point
glVertex2f(200, 100) # Coordinates of the lower right point
glVertex2f(200, 200) # Coordinates of the upper right point
glVertex2f(100, 200) # Coordinates of the upper left point
glEnd() # End drawing

# Initialize the window and display the square
def showScreen():
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT) # Remove everything from the display (i.e., turn everything white)
glLoadIdentity() # Reset the positions of all graphics/shapes
square() # Draw a square using our function
glutSwapBuffers()

glutInit()
glutInitDisplayMode(GLUT_RGBA) # Set the display mode to color
glutInitWindowSize(500, 500) # Set the width and height of your window
glutInitWindowPosition(0, 0) # Set the position of the window
wind = glutCreateWindow("OpenGL Coding Practice") # Set the window title
glutDisplayFunc(showScreen)
glutIdleFunc(showScreen) # Keep the window open
glutMainLoop() # Keep the window created above running in a loop

Explanation-

The above code creates an OpenGL window with the title “OpenGL Coding Practice” Practice,” sized 500×500 pixels, positioned in the upper left corner of the screen. It will create a colored window and continuously call the showScreen() function. Inside showScreen(), it clears the screen, resets the positions of the graphics/shapes, calls the “square” function (which draws the square using the specified vertex coordinates), and swaps the buffers. It will create a window with a fixed square, keep it open, and run in a loop.

However, our code isn’t complete yet. If we draw the square and clear the screen, we won’t be able to see it when it actually draws, as it will appear and disappear momentarily. Let’s write another function.

Code Example –

def iterate():
glViewport(0, 0, 500,500)
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
glOrtho(0.0, 500, 0.0, 500, 0.0, 1.0)
glMatrixMode (GL_MODELVIEW)
glLoadIdentity()

Now, let’s merge all the code snippets into a single code file so that there is no ambiguity.

Code Example

```python
import from OpenGL.GL *
import from OpenGL.GLUT *
import from OpenGL.GLU *

w,h = 500, 500

def square():
glBegin(GL_QUADS)
glVertex2f(100, 100)
glVertex2f(200, 100)
glVertex2f(200, 200)
glVertex2f(100, 200)
glEnd()

def iterate():
glViewport(0, 0, 500, 500)
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
glOrtho(0.0, 500, 0.0, 500, 0.0, 1.0)
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()

def showScreen():
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
glLoadIdentity()
iterate()
glColor3f(1.0, 0.0, 3.0)
square()
glutSwapBuffers()

glutInit()
glutInitDisplayMode(GLUT_RGBA)
glutInitWindowSize(500, 500)
glutInitWindowPosition(0, 0)
wind = glutCreateWindow("OpenGL Coding Example")
glutDisplayFunc(showScreen)
glutIdleFunc(showScreen)
glutMainLoop()

Explanation

In the above code, we use The OpenGL.GLUT library creates a window and sets the display mode to GLUT_RGBA. We set the window’s size and position, create a window titled “OpenGL Coding Example,” and set the display and idle functions to the showScreen function.

The showScreen function clears the screen, loads the identity matrix, and calls the iteration function to set the viewport, projection matrix, and modelview matrix. We set the color of the square to be drawn and then call the square function to draw the square.

The glutMainLoop() function begins the main loop of the GLUT program and keeps the window open, displaying the square on the screen.

Conclusion

This tutorial introduced the use of OpenGL, a library for creating three-dimensional graphics. It covered downloading and installing the library and a sample program that demonstrates how to create basic shapes using OpenGL. The sample program also outlined some of the function calls used to draw shapes using the library. Overall, while using OpenGL can be challenging, it is a powerful tool for creating 3D graphics and offers a wide range of possibilities to experienced users.