Bresenham’s Circle Algorithm

Bresenham's Circle Algorithm

You want to program graphics? You’ve found it. Drawing basic shapes like circles is essential for graphics programmers. You must comprehend Bresenham’s circle drawing algorithm. Don’t be intimidated by the posh name. Bresenham’s algorithm is easy to implement and essential to any graphics library. This beginner-friendly guide explains things step-by-step. Before long, you’ll be drawing flawless circles and ready for advanced graphics themes. Programming graphics can be difficult, but with Bresenham’s approach and practice, you’ll learn it. Get your compiler and let’s begin! This will be entertaining.

Bresenham's Circle Algorithm
Bresenham’s Circle Algorithm

Understanding Bresenham’s Circle Algorithm

Bresenham’s circle algorithm plots an accurate circle on a computer screen. The algorithm chooses spots around the circle’s circumference. The next location that minimizes the error from the genuine circle is calculated at each step.

To draw the circle:

  1. Pick your center point (x0, y0) and radius r.
  2. Set x = 0 and y = r (the topmost point).
  3. Calculate the error e as (x+1)2 + (y-1)2 – r2. If e > 0, y = y-1. Else, x = x+1.
  4. Move to the new point (x, y). Repeat from step 3 until you reach the starting point.
  5. Connect the dots and voila! You have a circle.

Bresenham's Circle Algorithm

By iteratively stepping through points, this clever algorithm lets you achieve a smooth circle without needing advanced math. While simple, Bresenham’s method produces strikingly accurate results and enables many of the graphics we now take for granted.

Step-by-Step Implementation of Bresenham’s Algorithm

To implement Bresenham’s circle drawing algorithm, follow these steps:

  1. Set the circle radius (r) and center coordinates (a, b).
  2. Set x = 0 and y = r. This is your initial position on the circumference.
  3. Check if the pixel (x, y) lies inside the circle. If yes, then plot it.
  4. Now calculate the value of the decision parameter (d) for the current position:

d = 3 – 2*r

  1. Based on the value of d, move to the next position:
  2. If d < 0:

x = x + 1;

d = d + 4*x + 6;

  • Else if d > 0:

y = y – 1;

d = d + 4x – 4y + 10;

  • Else:

x = x + 1;

y = y – 1;

d = d + 4x – 4y + 10;

  1. Repeat steps 3 to 5 until x = y. This will complete the upper half of the circle.
  2. Now interchange x and y, and repeat steps 3 to 6 to complete the lower half of the circle.
  3. Your circle is now complete! By following these clearly laid out steps, you’ll be drawing perfect circles in no time. Let the creativity begin!

Applications and Examples of Bresenham’s Circle Algorithm

Bresenham’s Circle Algorithm has several useful applications in computer graphics and image processing.

Drawing Circles

The most obvious use of Bresenham’s algorithm is to draw pixelated circles on digital displays. By calculating the coordinates of points on the circumference of a circle, the algorithm can plot each point as a pixel to render the circle shape. This is useful for creating circular icons, shapes and cursors on low resolution screens.

Bresenham's Circle Algorithm

Image Processing

Bresenham’s algorithm is also employed in image processing techniques like circle detection. By scanning an image for circle-like shapes that match the pattern of points generated by the algorithm, circles in the image can be identified. This is an important tool used in applications like machine vision, medical imaging and automated quality control systems.

The algorithm’s efficiency and ability to draw high quality circles with limited resources made it an essential tool in the early days of digital graphics and continues to serve as a building block for more complex computer imaging techniques today. Though simple, Bresenham’s circle algorithm has had an outsized impact on the advancement of digital displays and imaging.

Mathematical Foundations Behind Bresenham’s Approach

To understand how Bresenham’s algorithm works, you need to understand some basic geometry and math.

Slope and the Unit Circle

The slope between (x1, y1) and (x2, y2) is (y2 – y1) / (x2 – x1). We want circumference points while drawing a circle. These points are all the same radius from the center.Sine and cosine can calculate x and y coordinates for any point on a unit circle (radius = 1). Example: (x, y) = (cos(t), sin(t)) is on the unit circle. Increase t from 0 to 2Ď€ to move the point along the circle circumference.

Bresenham’s algorithm turns on pixels based on this link between t and (x, y). At t = 0, it calculates (x, y), turns on that pixel, increases t slightly, and repeats. It draws a circle by incrementing t and computing new points.

Choosing how much to increase t each time is essential. Bresenham found the best “step size” for a smooth circle. His approach involves integer addition, subtraction, and multiplication—no trigonometry! Keeping things simple helped Bresenham draw digital circles efficiently.

Challenges and Future Prospects

Bresenham’s algorithm for circle drawing is not without its challenges and limitations.


The algorithm provides an approximation of a circle using a pixel grid. Higher resolution displays will show the jagged edges and imperfections in the shape. For applications requiring precision, Bresenham’s circle algorithm may not be the optimal solution.

The algorithm’s simplistic approach also means it cannot account for anti-aliasing, dithering or other techniques to improve the appearance of the rendered circle. Additional processing would be required to achieve a smooth circle that pleases the human eye.

While Bresenham’s circle drawing algorithm paved the way for rasterization of geometrical shapes, more advanced algorithms have since been developed that can overcome these challenges and shortcomings. The algorithm remains an important first step in the evolution of 2D computer graphics.

Examples and Visualizations of Bresenham’s Circle Algorithm

To better understand Bresenham’s circle algorithm, it helps to see some visual examples.

Example 1: Circle with a radius of 3

  • Start at (0,3)
  • Go to (3,0)
  • Then to (0,-3)
  • End at (-3,0)

This traces a circle with a radius of 3, starting from the 3 o’clock position and going counter-clockwise.

Example 2: Circle with a radius of 5

  • Start at (0,5)
  • Go to (5,0)
  • Then to (0,-5)
  • Next to (-5,0)
  • Finally back to (0,5)

This demonstrates a circle with a radius of 5 units, producing a larger circle than the previous example.

By incrementing the radius value in the algorithm, you can generate circles of any size. The key is picking the right increment values for x and y to produce a smooth circle perimeter. With some practice, you’ll be drawing perfect pixel circles in no time!


Bresenham’s algorithm makes computer circles easy to draw. It may appear hard, but it’s only math and logic. Following the procedures will produce beautiful pixel circles quickly. Why not try it yourself? Plot points in your preferred coding environment, whether Python, C++, or another. How a few lines of code may create a familiar shape will astound you. Hand-drawn circles are gone. Loop about in the digital world!

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