Scan Converting a Point

Scan Converting a Point

Ever wondered how computers draw on screens? What matters is scan conversion, which turns mathematical points and lines into pixels. As a newbie graphics programmer, scan conversion is essential for rendering any image. Since you have to start somewhere, we’ll cover scan converting a single point in this tutorial.

Learn how to take a point in space and determine which screen pixels should be lit up to represent it. We’ll examine the math behind transforming continuous coordinates to discrete pixels. We’ll make math simple and emphasize fundamentals. You’ll grasp how a point appears on the screen at the end and be ready to learn about lines, circles, and polygons.

Understanding Coordinate Systems: The Relationship Between Points and Pixels

To display a point on your screen, your device needs to translate its coordinates into pixels.

A point exists in a mathematical coordinate system, defined by an x and y value. These values determine a precise location, but they don’t correspond directly to pixels on your display.

Understanding Coordinate Systems: The Relationship Between Points and Pixels

Your screen has a fixed number of pixels – for example, 1920 pixels across and 1080 pixels down. To show a point, your device maps the point’s x and y coordinates to pixels on the screen. It calculates where that location would be on your display.

For example, the point (x=10, y=20) might end up being displayed at around pixel (x=193, y=217) on a 1920×1080 screen. The exact pixel will depend on your screen’s size and resolution.

By translating points into pixels, your device can render an image, shape or line by illuminating the appropriate pixels on your display. And that’s the basics of how scan converting works!

Introducing Scan Conversion: Converting Continuous Points to Discrete Pixels

When you want to display a continuous point on a digital screen, you have to convert it into discrete pixels. This process is called scan conversion.

To scan convert a point:

  1. Determine the center pixel. The point location will be rounded to the nearest pixel center.
  2. Choose a shape to represent the point. The most common shapes are squares, circles, and crosses. Let’s use a 5×5 square.
  3. Turn on the pixels inside the shape. All 25 pixels in the square will be lit up.
  4. Adjust intensity (optional). You can make the point brighter in the center and darker at the edges. This makes it appear more rounded.

By repeating this process for all points, you can transform an infinite continuous space into a finite grid of pixels. Scan conversion allows us to represent any point or shape on a digital display. Pretty cool, huh?

Sampling Methods for Scan Converting a Point

Sampling Methods for Scan Converting a Point

There are a few common ways to determine which pixels should be turned on when scan converting a point. The simplest is nearest neighbor sampling. This finds the pixel center closest to the point and turns on just that single pixel. While fast, this can look blocky. For a smoother result, bilinear sampling takes the four pixels nearest the point and turns them on partially based on the point’s distance from each pixel center. The farther the point is from a pixel, the less that pixel is turned on. Bilinear sampling provides a good blend of speed and quality.

Sampling Methods for Scan Converting a Point

For the highest quality, bicubic sampling considers sixteen surrounding pixels and smoothly blends them based on the point’s distance. Bicubic sampling produces beautifully anti-aliased points but requires more processing power. If quality is key and you have the computing resources, bicubic is a great choice. If speed and simplicity are priorities, stick with nearest neighbor or bilinear.

In the end, the sampling method you choose depends on your needs. Evaluate factors like output quality, processing constraints, and runtime performance. The optimal technique for a real-time game will differ from that of a high-resolution image. With experimentation, you’ll find the perfect balance of quality and efficiency for your project.

Implementing Point Sampling in Code

To implement point sampling in code, you’ll need to:

  • Define a point struct to store x and y coordinates
  • Get the point’s coordinates from user input
  • Calculate the pixel coordinates from the point coordinates

Once you have the pixel coordinates, you can plot the point on the screen. Let’s walk through an example in C++:


struct Point {

float x;

float y;


int main() {

Point point;

std::cout << "Enter point coordinates: ";

std::cin >> point.x >> point.y;

// Get screen width and height

int screenWidth = 1024;

int screenHeight = 768;

// Calculate pixel coordinates

int pixelX = (point.x / screenWidth) * screenWidth;

int pixelY = (point.y / screenHeight) * screenHeight;

// Plot the point at (pixelX, pixelY)

// ...



This code creates a Point struct for point coordinates. After prompting the user for point coordinates, it stores them in the point variable. Next, it divides point coordinates by screen dimensions and multiplies by screen resolution to get pixel coordinates. This “scales” point coordinates to pixels. Finally, it can plot (pixelX, pixelY) to render the point on screen.

And that’s the basics of implementing point sampling in code! Let me know if you have any other questions.

Advanced Techniques for Improved Point Sampling

Advanced Techniques for Improved Point Sampling

To improve sampling of your point, try some advanced techniques.


Render your point at a higher resolution than your image, then scale down. This helps avoid aliasing artifacts. Rendering at 4x resolution, then scaling down to your target resolution is a good start.

Adaptive supersampling

Render at higher resolution only around the edges of your point. The center can remain at normal resolution. This focuses computing power where it’s needed most.


Render your point multiple times at different subpixel offsets, then average the results. This helps reduce aliasing and produces a smoother point. Most graphics APIs like OpenGL and Direct3D support multisampling.

Anisotropic filtering

When your point is at an oblique angle to the image plane, it appears elliptical. Anisotropic filtering renders the point at a higher resolution in the direction of the ellipse to keep it looking like a proper circle.

Alpha blending

For the best-looking points, render them with an alpha channel and blend them with the background. This produces soft, anti-aliased edges and a very natural appearance. Most graphics APIs support alpha blending.

With some experimentation, you can achieve beautiful results and gain valuable experience in rendering techniques. Keep at it and your skills will grow in no time!


That concludes a brief overview of scan converting a point. Breaking it down step-by-step simplifies it. So now you know how a point on your screen represents several pixel values and how those pixels light up. It’s amazing how a basic principle fuels all digital images. Next time you see a point on your smartphone, you’ll understand the work behind it. Happy scan conversion, learning, and fun!


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