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From: stevec@Apple.COM (Steve Christensen)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Easy way to draw the rubber band??
Message-ID: <53513@apple.Apple.COM>
Date: 31 May 91 04:59:58 GMT
References: <30149@hydra.gatech.EDU>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 63

gt4586c@prism.gatech.EDU (WILLETT,THOMAS CARTER) writes:
>i'm trying to draw the nifty rubber band we all know and love, the one that
>is a rectangle defined by the mouse location at the time of button down as
>the anchor point and the current mouse location (still with button down) as
>the other corner.  i've got the mouse location and drawing the rectangle
>alright, but it blanks out my drawing as it goes because i'm calling 
>EraseRect do blank out the rectangles outline as the mouse moves.  what's
>the right way to do it?  thanks for any help

If you just want to track an empty rectangle around, how about doing something
like this:

void RubberBand(Point startPt, Rect *theRect) {
  Point lastPt,newPt;

  lastPt.v = startPt.v;			// initialize the last mouse location
  lastPt.h = startPt.h;			//  to be the starting mouse location
  SetRect(theRect,0,0,0,0);		// empty rectangle to start

  PenMode(patXor);			// use XOR transfer mode

  while (StillDown()) {
    GetMouse(&newPt);			// get the mouse's current location
    if ((newPt.v != lastPt.v) && (newPt.h != lastPt.h)) {
      lastPt.v = newPt.v;		// it's moved since last time, so
      lastPt.h = newPt.h;		//  update the last location

      FrameRect(&theRect);		// erase the previous rectangle

      if (lastPt.v > startPt.v) {	// make sure the bottom of the
        theRect->top = startPt.v;	//  rectangle is below the top
        theRect->bottom = lastPt.v;
      } else {
        theRect->top = lastPt.v;
        theRect->bottom = startPt.v;
      }
      if (lastPt.h > startPt.h ) {	// ditto with the left and right
        theRect->left = startPt.h;
        theRect->right = lastPt.h;
      } else {
        theRect->left = lastPt.h;
        theRect->right = startPt.h;
      }

      FrameRect(theRect);		// draw the new rectangle
    }
  }

  PenNormal();				// restore the pen mode
}


Note that startPt should be in local coordinates.  This means you've done a
SetPort() to the appropriate port followed by GlobalToLocal(&startPt).
If you'd like a gray rubber band instead of a black one, you could also do
a PenPat(&qd.gray) (MPW) or PenPat(gray) (Think) right after the PenMode call.

steve

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Steve Christensen			Never hit a man with glasses.
  stevec@apple.com			Hit him with a baseball bat.