DispBegin

DispBegin

Begin buffering screen output

Syntax

      DispBegin() --> NIL

Returns

DispBegin() always returns NIL.

Description

DispBegin() is a screen function that informs the Harbour display output system that the application is about to perform a series of display operations.

Use DispBegin() with DispEnd() to allow the display output system to buffer display updates. Display output which occurs after DispBegin() but before DispEnd() is allowed to accumulate in internal buffers. When DispEnd() executes, any pending updates appear on the physical display. This is useful in applications where complex screen displays are slow and the appearance of performance is desired.

DispBegin() and DispEnd() calls are optional. They are not required for normal output.

Notes

. Nested calls: DispBegin() calls are nested internally. If several DispBegin() calls occur, buffering is allowed until a corresponding number of DispEnd() calls occur.

. Guaranteed operations: Display updates performed between DispBegin() and DispEnd() are not guaranteed to be buffered–some updates may become visible before DispEnd() is called. However, all updates are guaranteed to be visible after the closing call to DispEnd().

. Terminal operations: Terminal input operations such as INKEY() or READ should not be performed between DispBegin() and DispEnd(). Doing this may cause input or display output to be lost.

. Incompatible operations: Display output by other than the Harbour display functions (e.g., by add-on libraries or by DOS via OUTSTD(), etc.) may not be compatible with DispBegin() and DispEnd(). Output may be lost.

Examples

      .  This example buffers screen output, updates the screen, and
      then displays the buffered screen output:

      DispBegin()            // Start screen buffering
      //
      SETPOS(10, 10)
      DISPOUT("A display update")
      SETPOS(11, 10)
      DISPOUT("Another display update")
      //
      DispEnd()               // Display buffered screen data

Seealso

DispCount(), DispEnd()

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