Fade.java

Below is the syntax highlighted version of Fade.java from §3.1 Using Data Types.

/******************************************************************************
 *  Compilation:  javac Fade.java
 *  Execution:    java Fade n image1.jpg image2.jpg
 *  Data files:   https://introcs.cs.princeton.edu/java/31datatype/darwin.jpg
 *                https://introcs.cs.princeton.edu/java/31datatype/mandrill.jpg
 *
 *  Produce animated effect, fading from image1.jpg to image2.jpg,
 *  using n-1 intermediate frames.
 *
 *
 ******************************************************************************/

import java.awt.Color;

public class Fade {

    public static Color combine(Color c1, Color c2, double alpha) {
        int r = (int) (alpha * c1.getRed()   + (1 - alpha) * c2.getRed());
        int g = (int) (alpha * c1.getGreen() + (1 - alpha) * c2.getGreen());
        int b = (int) (alpha * c1.getBlue()  + (1 - alpha) * c2.getBlue());
        return new Color(r, g, b);
    }

    public static void main(String[] args) {
        int n = Integer.parseInt(args[0]);         // # of frames
        Picture picture1 = new Picture(args[1]);   // begin picture
        Picture picture2 = new Picture(args[2]);   // end picture

        if (picture1.width() != picture2.width()) {
            throw new IllegalArgumentException("pictures must have same width");
        }
        if (picture1.height() != picture2.height()) {
            throw new IllegalArgumentException("pictures must have same height");
        }

        int width  = picture1.width();
        int height = picture1.height();
        Picture picture = new Picture(width, height);
        for (int k = 0; k <= n; k++) {
            double alpha = 1.0 * k / n;
            for (int col = 0; col < width; col++) {
                for (int row = 0; row < height; row++) {
                    Color c1 = picture1.get(col, row);
                    Color c2 = picture2.get(col, row);
                    picture.set(col, row, combine(c2, c1, alpha));
                }
            }
            picture.show();
        }
    }
}