Introduction Working With Video Functions This module discusses video functions that are either directly or indirectly concerned with the screen. Included are all functions that deal with such screen adapters as CGA, EGA and Hercules. Different modes on various adapters are supported, such as a 40-column CGA, a 43- line EGA, or a 50-line VGA. DSETWINDOW() Many of the functions in this chapter depend on setting the DSETWINDOW() switch. This switch determines if the screen output of external programs, as well as DOS, are redirected to a window. Clipper Tools output functions are also valid as external. If the default setting in DSETWINDOW() is .T. or on, this rerouting is carried out. Some functions will then return inaccurate, or at the very least, different results. Examples of this are ISANSI() or NUMCOL() Attribute Many of the functions in this module work with color attributes designated as parameters. These arguments are carried out in three different ways: A numeric value, which corresponds to a combined color attribute (e.g., 7). A string in the "NN/NN" form, with two specified numeric values (e.g., "7/0"). A string in the "CC/CC" form, with two specified attributes are designated in the form Clipper requires (e.g., "W/N"). With many functions, the attribute returns a combined numeric value. Attributes for the foreground and background are tied together this way. Color attributes are constructed as follows: Bit 8 7 6 5 4 3 2 1 Attribute * R G B + R G B _ _ _ _ _ _ / _ _ _ _ _ _ Background / Foreground Each attribute consists of four bits, which represent a value in the range of 0 to 15. Therefore, there are a total of 16*16, or 256, different values from 0 to 255. These numeric values can be changed into the "nn/nn" format, that can be used under Clipper with the NTOCOLOR function. However, it is possible to directly influence this combined attribute value. The following examples show this and relate back to the chapter on number and bit manipulation: NUMOR( nattr, 128) // Flashing on NUMAND(nattr, 127) // Flashing off NUMXOR(nattr, 128) // Change flashing NUMOR(nattr, 8) // High intensity on NUMAND(nattr, 247) // High intensity off NUMXOR(nattr, 8) // Switch high intensity Special Parameter Type With many functions, a parameter may be of the <mIcCharacter|nCharacter> type (e.g., an individual character). This can occur in two different ways: Numerically, as the ASCII code of the desired character (e.g., 7). Alphanumeric as the character (e.g., ":"). Because of this, you must not use the CHR() function to change special characters. CLEARA and CLEARB Some of the Clipper Tools functions use a standard attribute and character to delete lines or screen areas. This attribute is described as CLEARA; the character as CLEARB. You can query both CLEARA and CLEARB with the corresponding functions. At the same time, certain preset values are in effect for CLEARA and CLEARB. The attribute "W/N" is the standard preset for CLEARA, while CHR(255) is the character used for CLEARB. If you use this character for CLEARB, it fills the background with the corresponding color for every deletion on every screen adapter. Use the following functions to set standard values for CLEARA and CLEARB: GETCLEARA() SETCLEARA() GETCLEARB() SETCLEARB() If you use the SETCLEARx() functions in conjunction with the corresponding parameters (<Attribute> or <Character>), the currently existing default value is replaced by a parameter. Clipper Functions and Commands Which Delete If you use the Clipper Extended Drivers, CHR(255) is used instead of a space for all Clipper functions and commands that delete the screen in one way or another (see CLEARB). A CHR(255) is helpful on many screen adapters, since in contrast to a space, you can assign it a color. Then, the screen will not appear so fuzzy. More precisely, the functions and commands concerned always use the delete character set by SETCLEARB(), which uses CHR(255) as the default setting. If you want to use a space to clear in Clipper or Clipper Tools, insert a SETCLEARB(32) into the program. Re-implement a space for clear: SETCLEARB(32) CLEAR // The affected Clipper command Video Modes Occasionally, there is some confusion about video modes. You will not be able to work in EGA mode just because your computer has an EGA adapter built into it. By the same token, you will not get either EGA or VGA modes, if you do not work with graphics. EGA43 / VGA50 / VGA28, etc. In this section, the concern is not to just get a mode "hardwired"' into a card, but for Clipper Tools it is to generate corresponding fonts and other settings. For these reasons, the GETMODE() and GETSCRMODE() functions generate their own values that are greater than 255. For example, changes to the screen mode concerned with line count can be combined with a 40-column mode: CGA40() EGA43() // 43 lines and 40 columns Video Functions and Windows You cannot implement functions that change the base address for screen memory while windows are open. This includes all mode changes, as well as SETPAGE and SETSCRSTR.
Since this section is about DOS-TEXT mode programming, considered as obsolete and details skipped.