"Snapped" form resize like in Delphi 7 Object Inspector

[hwnd]

Thanks you for this!
You forgot to declare VerticalBorderHeight.

But why the bottom part flickers so much? The right side seems ok, but bottom part is flickering.
The form wants to resize but it cant and flickers.

Even if i set doublebuffered to true and comment out the grid drawing.

EDIT
I downloaded some old free open source Delphi Object Inspector "clone" for Delphi 3 and it had the snapping in it.

Drop a DrawGrid on form, set fixedcols,fixedrows to 0, defaultcolwidth to 64, defaultrowheight to 64. Thats the tilesize i use.
And set Align of DrawGrid1 to alClient.

// Add this to private section of Form1
Procedure WhileSizing(Var msg : tmessage);  Message WM_SIZING;


procedure TForm1.WhileSizing(var msg: tmessage);

var PR : PRect;                              { Makes it so there's never half }
     Offset, offset2 : Integer;                        { a row showing in the listbox. }
     Growing : Boolean;
     Top, left : Boolean;
     Lb :tdrawgrid;
Begin
 Lb := DrawGrid1;
  if not (msg.wparam in [wmsz_top, wmsz_topleft, wmsz_topright,
                         wmsz_bottom, wmsz_bottomleft, wmsz_bottomright]) then exit;
  pr := Pointer(msg.Lparam);
  if (pr.bottom - pr.top) = height then exit;
  msg.result:= 1;

  OffSet := ((pr.bottom - pr.top) - (height - Lb.clientheight)) mod lb.DefaultRowHeight;
  Growing := (pr.bottom - pr.top) > height;
  top := msg.wparam in [wmsz_top, wmsz_topleft, wmsz_topright];
  //left := msg.WParam in [wmsz_bottom, wmsz_bottomleft, wmsz_bottomright ];

  if top then Begin
    if growing then
      pr.top := pr.top + offset
    else
      pr.top := pr.top - (lb.DefaultRowHeight  - offset);
  End Else Begin
    if Growing then
      pr.bottom := pr.Bottom - offset
    else
      pr.bottom := pr.bottom + (lb.DefaultRowHeight  - offset);
  End;

end;

It works the way i need, but i must make this work for right side also.
If anybody would like to help with this, then please.

Atm im watching and reading that code, because i dont understand everything in it.
If i would know i would convert it by myself.

I probably have to take piece of paper and pencil and calculate everything on that until i get it. Then i should be able to convert it to left and right side resizing.