private void drawIsolines() {
        double scaleW = (double)SIZE_W/(double)model.N;
        double scaleH = (double)SIZE_H/(double)model.M;

        for(int n = 0; n<model.N;n++){
            for (int m = 0; m<model.M;m++){
                int x1 = (int)(scaleW*(double)n+0.5);
                int x2 = (int)(scaleW*(double)(n+1)+0.5);
                int y1 = (int)(scaleH*(double)m+0.5);
                int y2 = (int)(scaleH*(double)(m+1)+0.5);
                drawIsolinesAt(new Point(x1,y2),
                        new Point(x2,y2),
                        new Point (x1,y1),
                        new Point (x2,y1));
            }
        }
    }

    public void drawIsolinesAt(Point p1,
                               Point p2,
                               Point p3,
                               Point p4) {
        double z = model.IsVal;

        drawIsolinesAt(p1,p2,p3,p4,z);
    }

    public void drawIsolinesAt(Point p1,
                               Point p2,
                               Point p3,
                               Point p4,
                               double z){

        Point topP = getPoint(p1,p2,z);
        Point rightP = getPoint(p2,p4,z);
        Point botP = getPoint(p4,p3,z);
        Point leftP = getPoint(p3,p1,z);

        ArrayList<Point> points = new ArrayList<>();
        if(topP!=null)points.add(topP);
        if(rightP!=null)points.add(rightP);
        if(botP!=null)points.add(botP);
        if(leftP!=null)points.add(leftP);

        if(points.size() == 2){
            drawLine(points.get(0),points.get(1));
        }
        if(points.size() == 4){
            Point midPoint = new Point( (p2.x+p3.x)/2,(p2.y+p3.y)/2);
            double midVal = model.getFuncValFor(midPoint)-z;
            double val1 = model.getFuncValFor(p1)-z;
            double val2 = model.getFuncValFor(p2)-z;
            if(val1*midVal<0) {
                drawLine(topP, leftP);
                drawLine(botP, rightP);
            }
            if(val2*midVal<0){
                drawLine(topP,rightP);
                drawLine(botP,leftP);
            }
        }
    }

    private void drawLine(Point p1, Point p2){
        Graphics g = canvas.getGraphics();
        Color tmpCol = g.getColor();
        g.setColor(new Color(model.IsColor));
        g.drawLine(p1.x,p1.y,p2.x,p2.y);
        g.setColor(tmpCol);
    }


    private Point getPoint(Point p1, Point p2, double z) {
        double f1 = model.getFuncValFor(p1);
        double f2 = model.getFuncValFor(p2);
        if((f1 < z && z < f2 )|| (f2 < z && z < f1)){
            double dx = -(p1.x - p2.x);
            double dy = -(p1.y - p2.y);
            int x = (int)(p1.x + dx*(z-f1)/(f2-f1));
            int y = (int)(p1.y + dy*(z-f1)/(f2-f1));

            return new Point(x,y);
        }else{
            return null;
        }

    }