Boulder Valley School District - Java Libraries

Version 2.0 - Monarch High School, Coding Capstone Class, 2023-2024 and J. Cihlar

©2024-2025

Overview

This Java library was developed for introductory AP Computer Science A students to engage in graphics programming without having to learn the nuances of the AWT library. The goal is to expose an easier-to-use set of methods that will generate simple shapes and process images in a more intuitive way.

This library comprises the following classes:

• Graphics: Used for generating simple 2D shapes. This class works independently from Image, Pixel, and Filter
• Image: Used to create and load raster images and apply effects. Uses the Pixel class.
• Pixel: Used to represent individual pixel data in the RGB color space.
• Filter: A class intended to teach inheritance and polymorphism. This class should be subclassed with filter-specific instance variables, a constructor that sets them and calls the super constructor. The apply method should be overriden to implement the specific filter effects.

Dependencies

The Graphics class utilizes JFree organization's SVG library so that the output can be in raster instead of vector format.

Before building, the JFree SVG library (Download link) should be downloaded as a .jar file and added to the classpath.

Building

No build manager is used because of the range of environments found in a K-12 environment. An already-built .jar file can be found in the target folder.

Usage

Once built (or if the .jar file is downloaded), add the .jar file to the classpath.

Use the import statement:`

import org.bvsd.*; // imports all classes

Minimal Examples

Graphics

This example creates a graphics object 200x200 pixels. It draws a simple circle with radius of 50 pixes in the middle, and saves it to a file called "circle.svg".

Graphics graphics = new Graphics(200, 200);
graphics.drawCircle(100, 100, 50);
graphics.saveToFile("circle.svg");

Image from File

This example loads a test image from file, increases the Red channel to 255, and saves the file. This does not use the Filter class.

try {
    Image img = new Image("testImage.png");
    Pixel [][] pixels = img.getPixels();
    for (int row = 0; row < pixels.length; row++) {
        for (int col = 0; col < pixels[col].length; col++) {
            pixels[row][col].setRed(255);
        }
    }
    Image newImage = new Image(pixels);
    newImage.saveToFile("testMaxRed.jpg", Image.FORMAT.JPG);

}
catch(IOException e) {
    System.err.println("Could not read/write file because: "+e.getMessage());
}

Blank Image

This example creates a blank image 1024x1024. It sets every other column to black.

try {
    Image img = new Image(1024, 1024);
    Pixel [][] pixels = img.getPixels();
    for (int row = 0; row < pixels.length; row++) {
        for (int col = 0; col < pxls[col].length; col+=2) {
            pixels[row][col].setRed(0);
            pixels[row][col].setGreen(0);
            pixels[row][col].setBlue(0);
        }
    }
    img.setPixels(pixels);
    img.saveToFile("testEveryOther.jpg", Image.FORMAT.JPG);

}
catch(IOException e) {
    System.err.println("Could not read/write file because: "+e.getMessage());
}

Filter

Implement a Filter by implementing the Filter interface. There is one required method that has the signature: public Image apply(Image img);

The filter below maxes out a given color specification.

public class MaxChannelFilter implements Filter {
    public enum COLOR {RED, GREEN, BLUE};
    private COLOR channel;

    public MaxChannelFilter(COLOR chan) {
        channel = chan;
    }

    public Image apply(Image img) {
        Pixel[][] pixels = img.getPixels();
        int mask;
        switch (channel) {
            case RED:
                mask = 0xFF0000;
                break;
            case GREEN:
                mask = 0xFF00;
                break;
            case BLUE:
                mask = 0xFF;
                break;
            default:
                mask = 0x0;
        }
        for (int row = 0; row < pixels.length; row++) {
            for (int col = 0; col < pixels[row].length; col++) {
                pixels[row][col].setRGB(pixels[row][col].getRGB() | mask);
            }    
        }
        return new Image(pixels);
    }
}

Team Members

• Stephen Buch
• Parth Chudappa
• Zach Dykstra
• Jonah Kim
• Josh Kim
• Ishani Pandey
• Yash Ruhil
• Max Webb
• Ben Willcutt
• Kevin Wong

Advised by Jon Cihlar