Screen Refresh Control¶

FWD introduces new WINDOW widget writable attribute DISABLE-REDRAW, its type is LOGICAL. The attribute can be used to temporarily disable redraw of a particular window. Note that only the "application" area of the window is affected, that is the area where FRAME and other widgets are placed. Window decorations (window title bar and borders), the message and status areas are not affected.

The usage:

CREATE WINDOW h.
h:DISABLE-REDRAW = TRUE.
/* window redraw is disabled */
/* any changes to the window content or child widgets won't be reflected in the window until DISABLE-REDRAW is set to FALSE again */
h:DISABLE-REDRAW = FALSE.
/* window redraw is enabled */

The motivation for the extension are two patterns commonly used to speed up window visual updates. First based on the WIN32 functions LockWindowUpdate (see example 1 below) and second based on the WM_SETREDRAW WIN32 window message (see example 2 below).

Example 1a:

PROCEDURE LockWindowUpdate EXTERNAL 'user32.dll':
  /* pass current-window:hwnd to suspend, set to 0 (zero) to enable again */
  DEFINE INPUT PARAMETER intWindowHwnd AS LONG NO-UNDO.
  DEFINE RETURN PARAMETER intResult AS LONG NO-UNDO.
END PROCEDURE.

RUN LockWindowUpdate (ACTIVE-WINDOW:HWND,OUTPUT i).
ASSIGN
  FRAME f:WIDTH-PIXELS = 100.
  FRAME f:HEIGHT-PIXELS = 100.
RUN LockWindowUpdate (0,OUTPUT i).

Example 1b (the above example re-written with the DISABLE-REDRAW extension):

ACTIVE-WINDOW:DISABLE-REDRAW = true.

ASSIGN
  FRAME f:WIDTH-PIXELS = 100.
  FRAME f:HEIGHT-PIXELS = 100.

ACTIVE-WINDOW:DISABLE-REDRAW = false.

Example 2a:

procedure SendMessageA external "user32.dll":
    define input  parameter hwnd   as long no-undo.
    define input  parameter wmsg   as long no-undo.
    define input  parameter wparam as long no-undo.
    define input  parameter lparam as long no-undo.
    define return parameter rc     as long no-undo.
end procedure.

procedure RedrawWindow external "user32.dll":
    def input parameter v-hwnd  as long no-undo.
    def input parameter v-rect  as long no-undo.
    def input parameter v-rgn   as long no-undo.
    def input parameter v-flags as long no-undo.
    def return parameter v-ret  as long no-undo.
end procedure.

PROCEDURE lockWindow :
  define input parameter phWindow as handle  no-undo.
  define input parameter plLock   as logical no-undo.

  define variable iRet as integer no-undo. 

  &GLOBAL-DEFINE WM_SETREDRAW     11
  &GLOBAL-DEFINE RDW_ALLCHILDREN 128
  &GLOBAL-DEFINE RDW_ERASE         4
  &GLOBAL-DEFINE RDW_INVALIDATE    1

  if plLock  then
  do:

    run SendMessageA( phWindow:hwnd
                    , {&WM_SETREDRAW}
                    , 0
                    , 0
                    , output iRet
                    ).
  end.
  else 
  do:
    run SendMessageA( phWindow:hwnd
                    , {&WM_SETREDRAW}
                    , 1
                    , 0
                    , output iRet
                    ).

    run RedrawWindow( phWindow:hwnd
                    , 0
                    , 0
                    , {&RDW_ALLCHILDREN} + {&RDW_ERASE} + {&RDW_INVALIDATE}
                    , output iRet
                    ).

  end. 
END PROCEDURE.

def var hpcbx as handle.
create combo-box hpcbx assign
   frame = FRAME f0:handle
   INNER-LINES = 14
   sensitive = true
   visible  = true
   row      = 3
   column   = 24.

run LockWindow (input active-window:handle, true).

hpcbx:INSERT('A', 'a', '1')
hpcbx:INSERT('B', 'b', '2')
hpcbx:INSERT('C', 'c', '3')
hpcbx:INSERT('B', 'b', '2')

run LockWindow (input active-window:handle, false).

Example 2b (the above example re-written with the DISABLE-REDRAW extension):

def var hpcbx as handle.
create combo-box hpcbx assign
   frame = FRAME f0:handle
   INNER-LINES = 14
   sensitive = true
   visible  = true
   row      = 3
   column   = 24.

ACTIVE-WINDOW:DISABLE-REDRAW = true.

hpcbx:INSERT('A', 'a', '1')
hpcbx:INSERT('B', 'b', '2')
hpcbx:INSERT('C', 'c', '3')
hpcbx:INSERT('B', 'b', '2')

ACTIVE-WINDOW:DISABLE-REDRAW = false.

FWD will not automatically convert the example 1a into 1b. Likewise FWD will not convert 2a into 2b. These WIN32 idioms are not automatically translated into the use of DISABLE-REDRAW. Any such changes must be manually written for now.

FWD does provide automated conversion of the 4GL cases 1b and 2b into Java. Any usage of the DISABLE-REDRAW attribute (on a WINDOW widget) will be automatically converted to the use of the method isDisableRedraw() (for reading the attribute) and setDisableRedraw(logical) or setDisableRedraw(boolean) for writing the attribute. The server-side implementation can be found in the com.goldencode.p2j.ui.WindowWidget.

© 2004-2017 Golden Code Development Corporation. ALL RIGHTS RESERVED.