====== Video Control=====
^Published By^Date^Version^Knowledge Level^Keywords^
|Sprezzatura Ltd|01 JUL 1992|2.12+|EXPERT|VIDEO, VCARD, GET_VID_INFO, VIDEOCONFIG, VIDCTRL, @CTRHIGH, @CTRMAXHIGH, INIT.STATUS, VIDEO.RW|
With the advent of more sophisticated video control (with 43 and 50 line
support) and with yet more sophistication to come (with the rumoured 132
column support) it is instructive to examine the system routines and control
records provided for the manipulation of the video screen. One thing that it
is timeous to point out is that whilst some of these routines (such as
VCARD) provide information that is accessible elsewhere, the use of calls to
standardised routines (such as GET_VID_INFO) is encouraged by RevTI as it
permits the construction of software "black boxes" which can be radically
changed on the inside without changing the result returned to the calling
program.
==== VIDEOCONFIG ====
There is a record in the SYSTEM file which contains the setup information
required when configuring the video mode. It has five multi-valued fields
as follows
|<1>|Video Mode - this is the numeric value used by VIDCTRL (q.v.) when resetting the video mode.|
|<2>|Description of the video mode|
|<3>|Screen width in this mode|
|<4>|Screen depth in this mode|
|<5>|Type of card mode will work with. Setting a VGA card to an EGA mode and vice versa does not work. This value records the kind of video card (as returned by VCARD (q.v.) which the video mode is designed for.|
==== VCARD ====
Called subroutine taking (and returning) one parameter, the kind of video
card installed. Calling syntax is X = "" ; CALL VCARD(X). Types identified
in Technical Bulletin 74 are, 0 - MDA, 1 - CGA, 2 - EGA, 3 - PGA, 4 - VGA,
5 - MCGA, 6 - Unknown.
==== GET_VID_INFO ====
This is a function taking one parameter - the branch, returning a result of
the information being asked for. The branches and returned results are as
follows
^Branch^Return Value^
|1|Video mode|
| |0 - Normal text mode|
| |1 - 25 line EGA Mode|
| |2 - 43 line EGA mode|
| |3 - 25 line VGA mode|
| |4 - 43 line VGA mode|
| |5 - 50 line VGA mode|
| |6 - 16 line VGA mode|
|2|CRT Width|
|3|CRT Height|
|4|Video Card type - same as results of VCARD.|
|5|Unknown - always returns 0 on test machine.|
|6|Starting address of Video RAM, returned as a two byte number, in low byte high byte order. Normally this would return CHAR(0) : CHAR(184), in other words (0 + 256 * 184) = 47104=B800.|
==== VIDCTRL ====
This assembler subroutine controls the video setting of the screen and can
be used to "flip" modes in real time. It takes 5 parameters, of which only
the first two and the last one seem to be used. As it is an assembler
routine it is difficult to be able to state with any confidence exactly what
all calls do, however there seem to be three major kinds of call, with each
kind taking a specific action modifier. The calling sequence is therefore
VidCtrl( Action, Mode, UK1, UK2, Flag)
where
|Action|Is the action to take, having the value of the video card type for modes 0 and 2, and the video mode to change to for mode 1.|
|Mode|Is the type of operation to be performed\\ \\ 0 Reset video card to default settings\\ 1 Change video mode\\ 2 Possibly initialise card - does not seem to be required.|
|UK|Unknown|
|Flag|Result of operation.|
Using this routine permits the programmer to reset the screen into an
alternative video mode. Note that when this is done there are several
caveats to be aware of :-
* Changing the screen size necessitates the changing of the status line location. This is done by resetting @CRTHIGH and @CRTMAXHIGH to the appropriate size and the calling the system routine INIT.STATUS.
* When video modes change, the screen is left blank. A background must therefore be filled in using Video.RW. In the code that follows the default background of \B01B\ is used. If you do not use the default and you wish to construct a generic routine, you will have to extract the correct settings from the environment.
* As mentioned in the discussion of VIDEOCONFIG, certain video modes do not work with certain video cards. The program following makes no allowance for this, but for genericism it could be coded to check the current video card against the requested mode by examining the VIDEOCONFIG record.
* As we wish to return to the normal status line when leaving the temporarily chosen mode, it is necessary to capture the screen image before the new mode is invoked, and restore this image upon return.
The code following represents a generic routine for calling a window from a
menu and having that window appear in a non-default video mode. It may be
called directly as a subroutine, or via catalyst using * to separate the
arguments. The arguments are the window name and the mode to use. The mode
can be the number or the text equivalent.
Subroutine Call_Window(Window, Mode)
Declare Subroutine VidCtrl, Catalyst, Video.Rw
Declare Function Guar_Assign, Get_Vid_Info
Mode = Guar_Assign(Mode)
If Index(Window, "*", 1) Then
Mode = Window[-1, "B*"]
Window = Window[1,"*"]
End
VidCard = "" ; Call VCard(VidCard)
ModeNums = "0,1,2,3,4,5,6"
Names = "TEXT,EGA25,EGA43,VGA25,VGA45,VGA50,VGA16"
ModeHigh = "25,25,43,25,45,50,16"
GoSub Save
Locate Mode In ModeNums Using "," Setting Pos
Then
DoIt = 1
End Else
Locate Mode In Names Using "," Setting Pos Then
DoIt = 1
End
End
If DoIt Then
GoSub SetUp
Catalyst("W", Window)
GoSub Restore
End
Return
SetUp:
Flag = "" ; VidCtrl(VidCard, 0, "", "", Flag)
Flag = ""
VidCtrl(Field(ModeNums,",",Pos), 1, "", "", Flag)
@CrtMaxHigh = Field(ModeHigh, ",", Pos)
@CrtHigh = @CrtMaxHigh
Video.RW(0,0,(@CrtWide-1),(@CrtHigh-1),"C",\B01B\)
Call Init.Status
Return
Save:
SaveMode = Get_Vid_Info(1)
SaveHigh = @CrtHigh
SaveMaxHigh = @CrtMaxHigh
Video.RW(0,0,@CrtWide-1,@CrtMaxHigh-1,"R",Image)
Return
Restore:
Flag = "" ; VidCtrl(VidCard, 0, "", "", Flag)
Flag = "" ; VidCtrl(SaveMode, 1, "", "", Flag)
@CrtMaxHigh = SaveMaxHigh
@CrtHigh = SaveHigh
Call Init.Status
Video.RW(0,0,@CrtWide-1,@CrtMaxHigh-1,"W", Image)
Return
(Volume 4, Issue 3, Pages 8-10)