Various display effects (color, underlining, reversed video, etc.)
and other attributes related to characters and edit lines are maintained
by shadow lines. Normally an edit line has no shadow line, but when at
least one character is typed in special display mode (turned on by the
FORMAT key, for example), the SURVO 84C system creates a shadow line
for the current line. Shadow lines are as long as normal edit lines,
i.e. ed1 bytes and they are saved in the order they are created after
the last normal edit line (ed2).
The shadow lines may contain any kind of characters. Space (blank) is
the default and means normal display on the screen. Characters `1', `2',
...,`7' are reserved for the current palette of colors (or display
effects). Their actual meaning can be controlled by the user (by editing
the auxiliary file SURVO.APU). These and other control codes are also
used in printing to produce various special effects.
The total amount of shadow lines is limited by the system parameter
edshad (default is 20). This limit may, however, be changed by the REDIM
operation. If the user tries to exceed the current limit, the system
gives a warning.
If a shadow line becomes empty, the system frees it for subsequent
use in the same edit field.
The shadow lines can be read and written as normal edit lines. The
index of the shadow line for the jth edit line is zs[j]. If there is no
shadow line, zs[j]=0.
The library function shadow_create is used to create new shadow lines
and shadow_test frees the shadow line if it consists of spaces only.
Normally the modules have no need to use shadow lines.
To illustrate working with shadow lines, we have made a small module
!SHADOW which creates and fills all the shadow lines of specific edit
lines with a selected character. For example, SHADOW 6,10,7 turns all
characters on lines 6-10 to inverse mode and SHADOW 1,END frees each
shadow line in the current edit field.
1 /* !shadow.c 28.3.1986/SM (28.3.1986)
2 SHADOW L1,L2,<shadow_character>
3 */
4 #include "survo.h"
5 #include "survoext.h"
6
7 main(argc,argv)
8 int argc; char *argv[];
9 {
10 int i,j,j1,j2;
11 char ch;
12 char shadow[LLENGTH];
13
14 if (argc==1) return;
15 s_init(argv[1]);
16 if (g<3)
17 {
18 sur_print("\nUsage: SHADOW L1,L2,<shadow_character>");
19 WAIT; return;
20 }
21
22 j1=edline2(word[1],1,1); if (j1==0) return;
23 j2=edline2(word[2],j1,1); if (j2==0) return;
24 if (g>3) ch=*word[3]; else ch=' ';
25 for (i=0; i<ed1-1; ++i) shadow[i]=ch;
26 shadow[ed1-1]=EOS;
27
28 for (j=j1; j<=j2; ++j)
29 {
30 if (zs[j]==0)
31 {
32 i=shadow_create(j);
33 if (i<0) return;
34 }
35 edwrite(shadow,zs[j],1);
36 if (ch==' ') shadow_test(j);
37 }
38 }
When referring to edit lines, both line numbers and line labels may
be used in SURVO 84C. Line labels are one character symbols written in
the control column of the edit field. Thus in modules which take line
labels as their parameters (as !SHADOW above) both alternatives must be
supported. This is done simply by using the library function edline2. It
was employed twice in !SHADOW (lines 22-23).