Question

I have a program in C# (Windows Forms) which has a rectangle on a Picture Box. They can be drawn at an angle too (rotated). I want to rotate that rectangle using my mouse movements.

I have the code for moving that rectangle

Rectangle areaRect = new Rectangle(100,100, 300, 300);
Bool dragging = false;
Point ptOld = new Point(0, 0);

protected override void OnPaint(PaintEventArgs e)
{
  Graphics dcPaint = e.Graphics;
  dcPaint.DrawRectangle(rectPen, areaRect);
}

protected override void OnMouseDown(MouseEventArgs e)
{
  ptOld = new Point(e.X, e.Y);
  dragging = true;
}

protected override void OnMouseMove(MouseEventArgs e)
{
  if(dragging = true) 
  {
    Point ptNew = new Point(e.X, e.Y);
    int dx = ptNew.X - ptOld.X;
    int dy = ptNew.Y - ptOld.Y;
    areaRect.Offset(dx, dy); // This one moves the rectangle 
    ptOld = ptNew;
    this.Invalidate();
  }
}

protected override void OnMouseUp(MouseEventArgs e)
{
  dragging = false;
}

Now My requirement is to rotate this rectangle, Any idea, how that can be achieved.

Answer 1

I think you want to calculate angle between two points on X-axis. If so, try the following code:

const double Rad2Deg = 180.0 / Math.PI;

return Math.Atan2(ptOld.Y - e.Y, e.X - ptOld.X) * Rad2Deg;

Also check out this article on calculating angle between two points