Java Language - Undo and Redo functions

Question

I’m doing a project where I develop functions to apply effects to photos (such as Contrast, Vignette, Sepia...).

As I apply effects to photos, the various states of the photos are being stored in an image array.

In this same project, I need two functions, Undo and Redo. Undo will be used to obtain the photo with the previously applied effect and Redo will be used to obtain the last applied effect.

Someone can help me in the development of these functions (Undo and Redo)?

Thank you.

Here’s what I got in class:

class Historico {

    private ColorImage [] VCI;
    private int atual;
    boolean undo = false;
    private int undos;
    private int redos;

    public Historico(ColorImage [] VCI) {
        this.VCI = VCI;
        atual = 0;
        undos = 0;
        redos = 0;
    }

    static ColorImage copy (ColorImage CI) {
        ColorImage NCI = new ColorImage(CI.getWidth(),CI.getHeight());
        for(int x = 0; x < CI.getWidth(); x++){
            for(int y = 0; y < CI.getHeight(); y++){
                Color c = CI.getColor(x,y);
                NCI.setColor(x,y,c);
                }
            }
        return NCI;
        } 

    void saveImage(ColorImage CI) {
        VCI [atual] = copy(CI);
        atual++;
        undo = false;
        undos = 0;
        redos=0;
    }

    public void undo() {
        ColorImage CI = copy(VCI[atual-2-undos]);
        VCI[atual] = CI;
        atual = atual + 1;
        undo = true;
        undos = undos + 2;
    }

    public void redo() {
        if(undo = true) {
            ColorImage CI = copy(VCI[atual-2-redos]);
            VCI[atual] = CI;
            atual = atual + 1; 
            undos--;
            if(undos<0){
                undos = 0;
                undo = false;
            }
            redos = redos + 2;
        }
    }   
}

Answer 1

You can use two lists as if they were stacks, one for the "undo" and one for the "redo". Also, when using lists instead of arrays, things will become much simpler to work with.

import java.util.List;
import java.util.ArrayList;

public class Historico {

    private final List<ColorImage> undos;
    private final List<ColorImage> redos;
    private ColorImage atual;

    public Historico() {
        this.undos = new ArrayList<>();
        this.redos = new ArrayList<>();
        this.atual = emBranco();
    }

    private static ColorImage emBranco() {
        return new ColorImage(256, 256);
    } 

    private static ColorImage copy(ColorImage ci) {
        ColorImage nci = new ColorImage(ci.getWidth(), ci.getHeight());
        for (int x = 0; x < ci.getWidth(); x++){
            for (int y = 0; y < ci.getHeight(); y++) {
                Color c = ci.getColor(x, y);
                nci.setColor(x, y, c);
            }
        }
        return nci;
    } 

    public void saveImage(ColorImage ci) {
        undos.add(atual);
        redos.clear();
        atual = ci;
    }

    public ColorImage undo() {
        if (!undos.isEmpty()) {
            redos.add(atual);
            atual = undos.remove(undos.size() - 1);
        }
        return atual;
    }

    public ColorImage redo() {
        if (!redos.isEmpty()) {
            undos.add(atual);
            atual = redos.remove(redos.size() - 1);
        }
        return atual;
    }

    public ColorImage getAtual() {
        return atual;
    }
}

Answer 2

You have reported that the states of the photos with each modification are stored in an image array, correct? I believe that your work would be simplified if, instead of using a vector, you used a double-chained list (Linkedlist). As it has references to both the previous and the later state of your image, the implementation of its Redo and Undo functions could be simplified only to the pointer movement that indicates the current position in your list through the Previous and Next methods of a Listiterator.