Texture Program by Notch

//Código do Notch

package net.minecraft.client.model.geom;

import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.*;
import java.util.*;
import java.util.List;

import javax.imageio.ImageIO;

import net.minecraft.client.model.dragon.DragonModel;
import util.Mth;

public class ImageGenerator {
    private static final int WIDTH = 256;
    private static final int HEIGHT = 256;

    private class Region {
        public int x1, y1, x2, y2;

        public Region(int x1, int y1, int x2, int y2) {
            this.x1 = x1;
            this.y1 = y1;
            this.x2 = x2;
            this.y2 = y2;
        }

        public void move(int xo, int yo) {
            x1 += xo;
            y1 += yo;
            x2 += xo;
            y2 += yo;
        }

        public boolean overlaps(Region r2, int xo, int yo) {
            if (r2.x2 + xo <= x1) return false;
            if (r2.y2 + yo <= y1) return false;
            if (r2.x1 + xo >= x2) return false;
            if (r2.y1 + yo >= y2) return false;
            return true;
        }

        public void render(Graphics g) {
            g.fillRect(x1, y1, x2 - x1, y2 - y1);
        }
    }

    private class UnfoldedCube {
        public int x, y;
        public Region[] cubeRegions = new Region[6];
        public String id;
        public int width, height;

        public UnfoldedCube(Cube cube) {
            int xs = Mth.ceil(cube.x1 - cube.x0);
            int ys = Mth.ceil(cube.y1 - cube.y0);
            int zs = Mth.ceil(cube.z1 - cube.z0);

            width = xs * 2 + zs * 2;
            height = zs + ys;

            id = cube.id;

            cubeRegions[0] = new Region(0, zs, zs, zs + ys);
            cubeRegions[1] = new Region(zs, zs, zs + xs, zs + ys);
            cubeRegions[2] = new Region(zs + xs, zs, zs + xs + zs, zs + ys);
            cubeRegions[3] = new Region(zs + xs + zs, zs, zs + xs + zs + xs, zs + ys);
            cubeRegions[4] = new Region(zs, 0, zs + xs, zs);
            cubeRegions[5] = new Region(zs + xs, 0, zs + xs * 2, zs);
        }

        public boolean fits(int x, int y) {
            for (int i = 0; i < 6; i++) {
                if (!isFree(cubeRegions[i], x, y)) return false;
            }
            return true;
        }

        public void place(int x, int y) {
            this.x = x;
            this.y = y;
            for (int i = 0; i < 6; i++) {
                cubeRegions[i].move(x, y);
                occupiedRegions.add(cubeRegions[i]);
            }
        }

        public void render(Graphics g) {
            float hue = (float) Math.random();
            g.setColor(new Color(Color.HSBtoRGB(hue, 1, 0.7f)));
            cubeRegions[5].render(g);
            g.setColor(new Color(Color.HSBtoRGB(hue, 1, 1.0f)));
            cubeRegions[4].render(g);
            g.setColor(new Color(Color.HSBtoRGB(hue, 1, 0.9f)));
            cubeRegions[1].render(g);
            cubeRegions[3].render(g);
            g.setColor(new Color(Color.HSBtoRGB(hue, 1, 0.8f)));
            cubeRegions[0].render(g);
            cubeRegions[2].render(g);
        }
    }

    private List<Region> occupiedRegions = new ArrayList<Region>();

    private boolean isFree(Region region, int xo, int yo) {
        if (region.x1 + xo < 0) return false;
        if (region.y1 + yo < 0) return false;
        if (region.x2 + xo > WIDTH) return false;
        if (region.y2 + yo > HEIGHT) return false;

        for (int i = 0; i < occupiedRegions.size(); i++) {
            if (occupiedRegions.get(i).overlaps(region, xo, yo)) return false;
        }

        return true;
    }

    public void generateImage(List<ModelPart> parts) {

        List<Cube> cubes = new ArrayList<Cube>();
        for (ModelPart mp : parts) {
            getCubes(mp, cubes);
        }

        Collections.sort(cubes, new Comparator<Cube>() {
            @Override
            public int compare(Cube c0, Cube c1) {
                int xs = Mth.ceil(c0.x1 - c0.x0);
                int ys = Mth.ceil(c0.y1 - c0.y0);
                int zs = Mth.ceil(c0.z1 - c0.z0);

                int ww0 = xs * 2 + zs * 2;
                int hh0 = zs + ys;

                xs = Mth.ceil(c1.x1 - c1.x0);
                ys = Mth.ceil(c1.y1 - c1.y0);
                zs = Mth.ceil(c1.z1 - c1.z0);

                int ww1 = xs * 2 + zs * 2;
                int hh1 = zs + ys;

                if (ww0 * hh0 < ww1 * hh1) {
                    return 1;
                } else if (ww0 * hh0 > ww1 * hh1) {
                    return -1;
                }

                return 0;
            }
        });

        List<UnfoldedCube> unfolded = new ArrayList<UnfoldedCube>();
        for (Cube cube : cubes) {
            UnfoldedCube uc = new UnfoldedCube(cube);

            boolean placed = false;
            positionLoop: for (int y = 0; y < HEIGHT - uc.height; y++) {
                for (int x = 0; x < WIDTH - uc.width; x++) {
                    if (uc.fits(x, y)) {
                        uc.place(x, y);
                        placed = true;
                        break positionLoop;
                    }
                }
            }
            if (!placed) {
                System.out.println("Failed to place " + uc.id);
            } else {
                unfolded.add(uc);
            }
        }

        BufferedImage img = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_ARGB);
        Graphics g = img.getGraphics();
        System.out.println("----------------");
        for (UnfoldedCube uc : unfolded) {
            System.out.println("setMapTex(\"" + uc.id + "\", " + uc.x + ", " + uc.y + ");");
            uc.render(g);
        }
        try {
            ImageIO.write(img, "png", new File("output.png"));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void getCubes(ModelPart mp, List<Cube> cubeList) {
        addLoop: for (Cube cube : mp.cubes) {
            if (cube.id != null) {
                for (Cube otherCube : cubeList) {
                    if (otherCube.id != null) {
                        if (otherCube.id.equals(cube.id)) {
                            System.out.println("Duplicate " + cube.id);
                            continue addLoop;
                        }
                    }
                }
            }
            cubeList.add(cube);
        }
    }

    public static void main(String[] args) {
        new ImageGenerator().generateImage(new DragonModel(0).cubes);
    }
}