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making a form snap-to the edge of the screen

Posted on 2000-04-15
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Last Modified: 2010-04-04
I should be able to figure this out by myself, but i keep on generating exceptions that crash my machine everytime i try.  So..

here is the question.  I'm trying to make my form (its a non-standard 'skinnable' form shape) snap to the edge of the screen once it reaches a certain distance from it.  I'm thinking I should be able to do this with with the WM_WINDOWPOSCHANGING message, but i'm not all that great with windows messageing yet.
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Question by:felonious
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5 Comments
 

Expert Comment

by:perkley
ID: 2719966
This is probably the easiest to understand and control, check it out.  You will want to read the article, and look at Option 3 in particular.

http://www.delphipages.com/news/detaildocs.cfm?ID=24
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Accepted Solution

by:
bryan7 earned 10 total points
ID: 2721554
this is how you do it.. works like winamp


     type
        TMovingSide = wmsz_Left..wmsz_BottomRight;
        TMovingSides = set of TMovingSide;

        TwmMoving = record
          Msg: Cardinal;
          Side: TMovingSides;
          Rect: PRect;
          Result: Longint;
        end;

  private
    DispLeft, DispTop, DispRight, DispBottom: Integer;
    procedure wmEnterSizeMove(var Message: TMessage); message wm_EnterSizeMove;
    procedure wmMoving(var Message: TwmMoving); message wm_Moving;

const
        SnapArea = 25;

procedure TForm1.wmEnterSizeMove(var Message: TMessage);
begin
 DispLeft:=0; DispTop:=0; DispRight:=0; DispBottom:=0;
end;

procedure TForm1.wmMoving(var Message: TwmMoving);
var
 OfsX, OfsY: Integer;
begin
 with Message.Rect^ do begin

  if Abs(DispLeft+Left)<SnapArea then begin
    OfsX:=-Left;
    DispLeft:=DispLeft+Left;
  end
  else begin
    OfsX:=DispLeft;
    DispLeft:=0;
  end;

  if Abs(DispRight+Right-Screen.Width)<SnapArea then begin
    OfsX:=Screen.Width-Right;
    DispRight:=DispRight+Right-Screen.Width;
  end
  else begin
    OfsX:=OfsX+DispRight;
    DispRight:=0;
  end;

  if Abs(DispTop+Top)<SnapArea then begin
    OfsY:=-Top;
    DispTop:=DispTop+Top;
  end
  else begin
    OfsY:=DispTop;
    DispTop:=0;
  end;

  if Abs(DispBottom+Bottom-Screen.height)<SnapArea then begin
    OfsY:=Screen.height-Bottom;
    DispBottom:=DispBottom+Bottom-Screen.height;
  end
  else begin
    OfsY:=OfsY+DispBottom;
    DispBottom:=0;
  end;

  end;
OffsetRect(Message.Rect^,OfsX,OfsY);
end;
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Author Comment

by:felonious
ID: 2721707
sorry perkley, i guess i should have made myself more clear about this question.  i HAVE to work through messageing (as MouseUp MouseMove MouseDown are not usable for my program).

bryan7:  works beautifuly.  thanks very much.
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Author Comment

by:felonious
ID: 2721776
one small problem though.  the form snaps to the the top of the screen just fine, but when the left mouse button is released it jumps down 2-4 pixels.  strange.
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LVL 3

Expert Comment

by:bryan7
ID: 2725061
"ouse button is released it jumps down 2-4 pixels.  s

it doesn't happen in my app..

?¿
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