Q:

Texture deforming, 4 points

i am writing simple 3d game in Java and i need code / lib for texture deforming. I don't want to use OpenGL.
Example:
I have got texture:

And i need deform it to:

I hope everybody can understand me. Thanks!

A:

OK, here we go. Implemented as a small, self-contained example where you can drag around the corners with the mouse:

+1 to...

tucuxi who already posted the basic approach in his answer
MvG at math.stackexchange.com who described how to compute a projective transformation from 4 points

Here's the code:
import java.awt.Color;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Point2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Pseudo3DTest
{
    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                createAndShowGUI();
            }
        });
    }

    private static void createAndShowGUI()
    {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        BufferedImage image = null;
        try
        {
            image = ImageIO.read(new File("lena512color.png"));
        }
        catch (IOException e)
        {
            e.printStackTrace();
            return;
        }
        f.getContentPane().setLayout(new GridLayout(1,2));
        f.getContentPane().add(new JLabel(new ImageIcon(image)));
        f.getContentPane().add(new Pseudo3DImagePanel(image));
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
}

class Pseudo3DImagePanel extends JPanel
    implements MouseListener, MouseMotionListener
{
    private final BufferedImage inputImage;
    private final Point2D p0;
    private final Point2D p1;
    private final Point2D p2;
    private final Point2D p3;
    private Point2D draggedPoint;

    Pseudo3DImagePanel(BufferedImage inputImage)
    {
        this.inputImage = inputImage;
        this.p0 = new Point2D.Double(30,20);
        this.p1 = new Point2D.Double(50,400);
        this.p2 = new Point2D.Double(450,300);
        this.p3 = new Point2D.Double(430,100);
        addMouseListener(this);
        addMouseMotionListener(this);
    }

    @Override
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);

        BufferedImage image = Pseudo3D.computeImage(inputImage, p0, p1, p2, p3);
        g.drawImage(image, 0, 0, null);

        int r = 8;
        g.setColor(Color.RED);
        g.fillOval((int)p0.getX()-r, (int)p0.getY()-r, r+r, r+r);
        g.fillOval((int)p1.getX()-r, (int)p1.getY()-r, r+r, r+r);
        g.fillOval((int)p2.getX()-r, (int)p2.getY()-r, r+r, r+r);
        g.fillOval((int)p3.getX()-r, (int)p3.getY()-r, r+r, r+r);
    }

    @Override
    public void mousePressed(MouseEvent e)
    {
        Point p = e.getPoint();
        int r = 8;
        if (p.distance(p0) < r) draggedPoint = p0;
        if (p.distance(p1) < r) draggedPoint = p1;
        if (p.distance(p2) < r) draggedPoint = p2;
        if (p.distance(p3) < r) draggedPoint = p3;
    }

    @Override
    public void mouseDragged(MouseEvent e)
    {
        if (draggedPoint != null)
        {
            draggedPoint.setLocation(e.getX(), e.getY());
            repaint();
        }
    }

    @Override
    public void mouseReleased(MouseEvent e)
    {
        draggedPoint = null;
    }

    @Override
    public void mouseMoved(MouseEvent e) {}
    @Override
    public void mouseClicked(MouseEvent e) {}
    @Override
    public void mouseEntered(MouseEvent e) {}
    @Override
    public void mouseExited(MouseEvent e) {}
}

class Pseudo3D
{
    static BufferedImage computeImage(
        BufferedImage image,
        Point2D p0, Point2D p1, Point2D p2, Point2D p3)
    {
        int w = image.getWidth();
        int h = image.getHeight();

        BufferedImage result =
            new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);

        Point2D ip0 = new Point2D.Double(0,0);
        Point2D ip1 = new Point2D.Double(0,h);
        Point2D ip2 = new Point2D.Double(w,h);
        Point2D ip3 = new Point2D.Double(w,0);

        Matrix3D m = computeProjectionMatrix(
            new Point2D[] {  p0,  p1,  p2,  p3 },
            new Point2D[] { ip0, ip1, ip2, ip3 });
        Matrix3D mInv = new Matrix3D(m);
        mInv.invert();

        for (int y = 0; y < h; y++)
        {
            for (int x = 0; x < w; x++)
            {
                Point2D p = new Point2D.Double(x,y);
                mInv.transform(p);
                int ix = (int)p.getX();
                int iy = (int)p.getY();
                if (ix >= 0 && ix < w && iy >= 0 && iy < h)
                {
                    int rgb = image.getRGB(ix, iy);
                    result.setRGB(x, y, rgb);
                }
            }
        }
        return result;
    }

    // From https://math.stackexchange.com/questions/296794
    private static Matrix3D computeProjectionMatrix(Point2D p0[], Point2D p1[])
    {
        Matrix3D m0 = computeProjectionMatrix(p0);
        Matrix3D m1 = computeProjectionMatrix(p1);
        m1.invert();
        m0.mul(m1);
        return m0;
    }

    // From https://math.stackexchange.com/questions/296794
    private static Matrix3D computeProjectionMatrix(Point2D p[])
    {
        Matrix3D m = new Matrix3D(
            p[0].getX(), p[1].getX(), p[2].getX(),
            p[0].getY(), p[1].getY(), p[2].getY(),
            1, 1, 1);
        Point3D p3 = new Point3D(p[3].getX(), p[3].getY(), 1);
        Matrix3D mInv = new Matrix3D(m);
        mInv.invert();
        mInv.transform(p3);
        m.m00 *= p3.x;
        m.m01 *= p3.y;
        m.m02 *= p3.z;
        m.m10 *= p3.x;
        m.m11 *= p3.y;
        m.m12 *= p3.z;
        m.m20 *= p3.x;
        m.m21 *= p3.y;
        m.m22 *= p3.z;
        return m;
    }

    private static class Point3D
    {
        double x;
        double y;
        double z;

        Point3D(double x, double y, double z)
        {
            this.x = x;
            this.y = y;
            this.z = z;
        }
    }

    private static class Matrix3D
    {
        double m00;
        double m01;
        double m02;
        double m10;
        double m11;
        double m12;
        double m20;
        double m21;
        double m22;

        Matrix3D(
            double m00, double m01, double m02,
            double m10, double m11, double m12,
            double m20, double m21, double m22)
        {
            this.m00 = m00;
            this.m01 = m01;
            this.m02 = m02;
            this.m10 = m10;
            this.m11 = m11;
            this.m12 = m12;
            this.m20 = m20;
            this.m21 = m21;
            this.m22 = m22;
        }

        Matrix3D(Matrix3D m)
        {
            this.m00 = m.m00;
            this.m01 = m.m01;
            this.m02 = m.m02;
            this.m10 = m.m10;
            this.m11 = m.m11;
            this.m12 = m.m12;
            this.m20 = m.m20;
            this.m21 = m.m21;
            this.m22 = m.m22;
        }

        // From http://www.dr-lex.be/random/matrix_inv.html
        void invert()
        {
            double invDet = 1.0 / determinant();
            double nm00 = m22 * m11 - m21 * m12;
            double nm01 = -(m22 * m01 - m21 * m02);
            double nm02 = m12 * m01 - m11 * m02;
            double nm10 = -(m22 * m10 - m20 * m12);
            double nm11 = m22 * m00 - m20 * m02;
            double nm12 = -(m12 * m00 - m10 * m02);
            double nm20 = m21 * m10 - m20 * m11;
            double nm21 = -(m21 * m00 - m20 * m01);
            double nm22 = m11 * m00 - m10 * m01;
            m00 = nm00 * invDet;
            m01 = nm01 * invDet;
            m02 = nm02 * invDet;
            m10 = nm10 * invDet;
            m11 = nm11 * invDet;
            m12 = nm12 * invDet;
            m20 = nm20 * invDet;
            m21 = nm21 * invDet;
            m22 = nm22 * invDet;
        }

        // From http://www.dr-lex.be/random/matrix_inv.html
        double determinant()
        {
            return
                m00 * (m11 * m22 - m12 * m21) +
                m01 * (m12 * m20 - m10 * m22) +
                m02 * (m10 * m21 - m11 * m20);
        }

        final void mul(double factor)
        {
            m00 *= factor;
            m01 *= factor;
            m02 *= factor;

            m10 *= factor;
            m11 *= factor;
            m12 *= factor;

            m20 *= factor;
            m21 *= factor;
            m22 *= factor;
        }

        void transform(Point3D p)
        {
            double x = m00 * p.x + m01 * p.y + m02 * p.z;
            double y = m10 * p.x + m11 * p.y + m12 * p.z;
            double z = m20 * p.x + m21 * p.y + m22 * p.z;
            p.x = x;
            p.y = y;
            p.z = z;
        }

        void transform(Point2D pp)
        {
            Point3D p = new Point3D(pp.getX(), pp.getY(), 1.0);
            transform(p);
            pp.setLocation(p.x / p.z, p.y / p.z);
        }

        void mul(Matrix3D m)
        {
            double nm00 = m00 * m.m00 + m01 * m.m10 + m02 * m.m20;
            double nm01 = m00 * m.m01 + m01 * m.m11 + m02 * m.m21;
            double nm02 = m00 * m.m02 + m01 * m.m12 + m02 * m.m22;

            double nm10 = m10 * m.m00 + m11 * m.m10 + m12 * m.m20;
            double nm11 = m10 * m.m01 + m11 * m.m11 + m12 * m.m21;
            double nm12 = m10 * m.m02 + m11 * m.m12 + m12 * m.m22;

            double nm20 = m20 * m.m00 + m21 * m.m10 + m22 * m.m20;
            double nm21 = m20 * m.m01 + m21 * m.m11 + m22 * m.m21;
            double nm22 = m20 * m.m02 + m21 * m.m12 + m22 * m.m22;

            m00 = nm00;
            m01 = nm01;
            m02 = nm02;
            m10 = nm10;
            m11 = nm11;
            m12 = nm12;
            m20 = nm20;
            m21 = nm21;
            m22 = nm22;
        }
    }

}

