Local coordinate system for 2D cad

lory1990

hi everyone! I'm coding a simple 2D CAD, the main problem is getting the Cartesian coordinate of the mouse pointer in the local cartesian system after a translation and/or a scale. I've done this and it works well for translation but not for scale :(

public class Plane3D extends PApplet {
    protected boolean mouse_in_out = false;
    @ Override
     public void setup(){
        background(255);
        addMouseWheelListener(new java.awt.event.MouseWheelListener() {
            @ Override
            public void mouseWheelMoved(java.awt.event.MouseWheelEvent evt) {
                mouseWheel(evt.getWheelRotation());
            }});
        this.addMouseListener(new MouseListener() {
            @ Override
            public void mouseClicked(MouseEvent me) {}
            @ Override
            public void mousePressed(MouseEvent me) {
                System.out.println("Qui siamo");
                X_start = mouseX;
                Y_start = mouseY;
            }
            @ Override
            public void mouseReleased(MouseEvent me) {
                System.out.println("Rilasciato");
                float dx = mouseX-X_start;
                float dy = mouseY-Y_start;
                System.out.println("dx:" + dx + "dy: " +dy );
                XO_coord += dx;
                YO_coord += dy;
            }
            @ Override
            public void mouseEntered(MouseEvent me) {
                mouse_in_out=true;
            }
            @ Override
            public void mouseExited(MouseEvent me) {mouse_in_out=false;}
        });
    }
    @ Override
    public void draw(){
        background(255);
        scaleUp = wheel;
        transScale(mouseX, mouseY, scaleUp);
    }; 
    //---- Coordinate System ----
    private float X_start,Y_start;
    public float X_coord;
    public float Y_coord;
    public float XO_coord;
    public float YO_coord;
    //---- Translation ----
    private float scaleUp = 0.5f;
    private float wheel =  1.0f;
    private float wheelMult = 0.10f;
    private float xOffset;
    private float yOffset;
    private float xold;
    private float yold;
    private float xpiv;
    private float xpivOld;
    private float ypiv;
    private float ypivOld;

    private void mouseWheel(int step) {
      wheel=constrain((float)wheel+step*wheelMult*-1,0.1f,100f);
    }
    protected void transScale(float x, float y,float scale) {
        if (mousePressed == true) {
        xOffset = x-xold;
        yOffset = y-yold;
        xpiv = (xpivOld-xOffset/scaleUp);
        ypiv = (ypivOld-yOffset/scaleUp);
        xpiv = xpiv + (xOffset/scaleUp);
        ypiv = ypiv + (yOffset/scaleUp);
        xpivOld = xpiv;
        ypivOld = ypiv;
        xold = x;
        yold = y;
        }
        else{
        xOffset = x-xold;
        yOffset = y-yold;
        xpiv = (xpivOld-xOffset/scaleUp);
        xpivOld = xpiv;
        ypiv = (ypivOld-yOffset/scaleUp);
        ypivOld = ypiv;
        xold = x;
        yold = y;
        }
        X_coord = (mouseX - XO_coord*scale)/scale;
        Y_coord = (mouseY - YO_coord*scale)/scale;
        // blue grid position
        translate(x, y);
        scale(scale);
        // negate mouse position
        translate(xpiv, ypiv);        
        //System.out.println("X:" + X_coord + "Y:" + Y_coord);
        System.out.println("X:" + modelX(mouseX,mouseY,0) + "Y:" + modelY(mouseX,mouseY,0));
    }

any ideas?