Drag polygon

[cassysumandak]

I draw many polygons, and later wanted to move some of the polygon to new location on screen using mouse drag. How can I drag the polygon using mouse and see it moving with the mouse drag?

[Fubarable]

I recommend that you use a MouseAdapter (MouseListener and MouseMotionListener combined). For more specific advice, you may wish to provide more detail and code.

[oxano]

int startX, startY, curX, curY;
boolean dragging = false;


//from the moment you press down the mousebutton it checks and stores the
//original mouse position and sets dragging boolean to true
public void mousePressed(mousEvent e){
   startX = e.getX();
   startY = e.getY();
   dragging = true; 
}

//Every time you move the mouse this method is called, you get the current
//mouse position and compare it with the original one(startX,startY) and you
//know to where it's draggging. Because it's called every time the mouse is
//moved, even with no pressing of the mouse, the boolean is important
public void mouseMoved(mouseEvent e){
   if(dragging){
      curX = e.getX();
      curY = e.getY();
      repaint() / Update() / redraw()  //whatever method you have
   
}

//when you release the mousebutton the boolean must be set back to false
public void mouseReleased(mouseEvent e){
   dragging = false;
}

example polygon with 5 corners:
1,2
4,9
6,7
3,5
7,8

then dragging begins: mousepressed -->mousemoved for a while -->mousereleased
the mousepressed sets startX and Y to 1,2
then after some mousemoved methods it reads for the curX and Y : 4,7
then you know you must redraw your polygon at the same X coordinates +(4-1) and Y +(7-2).

thus far the easy part.

hard part: how to know on which polygon you clicked and if you even clicked on 1 after all.
Do you want to detect it with code or do you have some sort of list in your GUI where all the drawn polygons are listed and you can select em that way?

[cassysumandak]

Thanks Oxano, with your explaination, I have changed my code and manage to drag the triangles successfully :-).

public class DrawingBoardWithMatrix extends JFrame implements MouseListener, ActionListener {

java.util.List<Polygon> triangles = new LinkedList<Polygon>();
Point startDrag,endDrag, midPoint;
Polygon selectedTriangle=null;
....

public PaintSurface() {  
        this.addMouseListener(new MouseAdapter() { 
        public void mousePressed (MouseEvent e) {
              startDrag = new Point(e.getX(), e.getY()); //First point
              endDrag = startDrag;
              repaint();     			
              //check the point is inside the triangle
              for (Polygon p:triangles){
                   if (p.contains(startDrag)) {    // mouse pressed inside triangle
                      selectedTriangle = p;
     	              break;
                   }
              }
        } //end mousePressed 
      			     		
        public void mouseReleased(MouseEvent e) {  
  	     if (selectedTriangle ==null) { //mouse pressed not within area of triangles, create new triangle
             .....
	          int[] xs = { startDrag.x, endDrag.x, midPoint.x };
                  int[] ys = { startDrag.y, startDrag.y, midPoint.y }; 
                  triangles.add(new Polygon(xs, ys,3)); //save to list
	     }
	     repaint();
	     endDrag   = null;
	     startDrag = null;
	     selectedTriangle=null;
        } //end mouseReleased

      });//end addMouseListener
    
      this.addMouseMotionListener(new MouseMotionAdapter() {
      public void mouseDragged(MouseEvent e) {
           endDrag = new Point(e.getX(), e.getY());
    
           if (selectedTriangle !=null) {	//mouse pressed inside polygon triangle
	         int xtrans = endDrag.x - startDrag.x;
	         int ytrans = endDrag.y - startDrag.y; 
	         selectedTriangle.translate(xtrans,ytrans);   //move existing triangle
	         repaint();
	         startDrag = endDrag;
           }
       } //end mouseDragged
      }); //end this.addMouseMotionListener      
}//end paintSurface       
        
public void paint(Graphics g) {
.....
}//end paint

[hawx]

excuse will be possible to let me see your code I need to make a tangram and the drag of the polygons have not been able to
thanks

[DarrylBurke]

Start your own thread and ask a specific question and you may get help.

Keep on saying gimmedacodez and you'll get nowhere. A forum is not a code factory.

db