Introduction Window Functions

Introduction

It is hard to imagine using Clipper without using windows. Windows
 are the best way to show multiple tasks so you can get a genuine
 overview of the system operation. The functions in this chapter offer a
 particularly valuable extension to Clipper in this area.

The Window System

If you are only working with one screen, the Clipper Tools functions
 permit up to 255 windows, depending on available memory. In conjunction
 with the MONISWITCH() function from the Video Function chapter,
 Clipper Tools can even support two screens linked to a single CPU,
 with one monochrome screen and one color screen. In this way two
 entirely independent window systems, each with 255 windows, are
 available.
The window functions take into account the fact that Clipper Tools
 supports larger screens than the common 25 rows x 80 columns. A screen,
 and therefore also a window, can be up to 255 rows or 255 columns in
 size. However, the complete contents of a screen can never require more
 than 32 KB of memory. So with 255 rows, no more than 128 columns are
 possible.
Moving Interactively
As soon as SCROLL LOCK is activated, the active window can be moved with
 different cursor keys. Depending on how you open them, windows can even
 overlap. The gray Plus key in the numeric key pad works like the
 function WCENTER(). You use the Plus key to move a partially visible
 window back into a completely visible area. All window movements done
 after you activate SCROLL LOCK can be undone using the ESC key.

Programming with Window Functions
. Each window is assigned a number between 1 and 255 when it is
 opened. This number is known as the window handle. Handle 0 is the
 original screen, with no open windows. The window handle returned
 will be used to refer to that window during programming. (For
 example, you need the window handle when you select a background
 window.)
WMODE(.T., .T., .T., .T.) // Overlap permitted
nWindow1 := WOPEN(....)
 nWindow2 := WOPEN(....) // This is the active window
WSELECT(nWindow1) // Activate first window
. The coordinates used for screen output are relative only to
 the selected window, and not the entire screen.
nWindow1 := WOPEN(....) // Selected window
@ 02, 02 SAY "Clipper Tools"
. Since a window behaves exactly as the normal screen would,
 QOUT() style output (?, ??, etc.) will be scrolled up as soon as it
 reaches the bottom row.
. The window in the following example, which extends to row 24,
 will not overwrite the help message on row 25:
@ 24, 00 SAY "........ HELP-ROW........"
 nWindow1 := WOPEN(0, 0, 23, 79) // Protects the last row
 FOR nI = 1 TO 100
 ? "Clipper Tools ...."
 NEXT nI
. A window displays as a full value, but is a virtual screen,
 which differs from the original physical screen only in size.
 Extended drivers make the MAXROW() and MAXCOL() functions available
 in a version enhanced over and above Clipper to accommodate the
 changed size. Now the coordinates of virtual screens can also be
 determined; these functions return the last row or column concerned
 with the currently selected window:
nWindow1 := WOPEN(10, 10, 20, 60)
? MAXROW() // Row: 10
 ? MAXCOL() // Column: 50
. The underlying screen area is saved automatically when a new
 window is opened. This applies equally to any area of the screen
 that becomes overlapped by the movement of a window. At the same
 time, all settings in the areas that have been overwritten are saved.
 These settings include cursor shape and position, as well as color
 attributes. So you do not have to save anything out of the affected
 screen area; Clipper Tools takes over this task automatically.
. The following example shows you how the window functions save
 both the color and cursor setting:
SET COLOR TO R // Set color RED
 ? "Test-Text 1 ..." // Output in RED
 nWindow1 := WOPEN(10, 10, 20, 55)
 WBOX() // RED window border
 SET COLOR TO BG // Set color CYAN
 ? "Test-Text 2 ..." // Output in CYAN
 INKEY(0) // Wait for keystroke
 WFCLOSE() // Close window again
? "Test-Text 3 ..." // Output again in RED
 // and directly below "Text 1"

Active Windows
After you close a window, the active window with the highest handle is
 the one selected, not the window that was previously active. If, for
 example, the highest window handle is 9 and window 5 was just selected,
 a newly opened window is assigned handle 10. However, after you close
 this window number 10, window 9 is selected. It is therefore important
 to save the window's handle to a variable when you open it, so that you
 can select the required window later.
You can save the active window handle by calling WSELECT() with no
 parameters.
. The external output of programs called with RUN within a
 Clipper program can be tied to windows:
DSETWINDOW(.T.)
 nWindow1 := WOPEN(10, 10, 22, 70)
 RUN DIR // Display results in window
The only prerequisite is that such output is through DOS or BIOS. The
 DSETWINDOW() function controls whether or not this output is
 subsequently redirected. The Extended Driver chapter has more details.
In addition to the examples shown here there are many more window
 functions available for use that contribute to a comprehensive windows
 system.

Note : "Window" concept of Clipper Tools related only text (DOS) mode 
programming. It's superseded by GUI programming concepts and at least 
GT (General Terminal) facilities of Harbour.