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researchv10 Dan Cross

.TH MOVETO 3L "630 MTG"
.SH NAME
moveto, sPtCurrent \- change and return the value current screen point
.SH SYNOPSIS
.ft B
#include <dmd.h>
.sp
void moveto (p)
.br
Point p;
.sp
\f3Point sPtCurrent ( )\f1
.sp
\f3extern int didmoveto;\f1
.ft R
.SH DESCRIPTION
These functions can be used to change or return the value 
of the current screen point. The current screen point is simply a place holder
that applications can use to manage current screen position. 
For example, the \fIlputchar\fR function uses 
.I sPtCurrent
to find the point at which to print the next character and uses
.I moveto
to update the current screen point after it prints the character.

The current screen point is similar to but distinct
from \fIPtCurrent\fR (see \fIglobals\fR(3R)). The primary difference is that
the current screen point is stored in screen coordinates, and
the
\fIPtCurrent\fR is stored in window coordinates (see \fItransform\fR(3R)). 
This makes the 
current screen point easier to deal with for applications that want to 
work completely in screen coordinates.

The \fImoveto\fR function will move the current screen
point to the point \fIp\fR. The \fIsPtCurrent\fR
function returns the value of the current screen point.

The current screen point is actually stored in the variable
P->scurpt. It is stored as an offset from Drect.origin
(i.e., sub[p, Drect.origin]). Note that this refers only to internal
representation. The functions \fImoveto\fR and \fIsPtCurrent\fR work in actual
screen coordinates and translate the offset on each call.

Storing the current screen point as
an offset from Drect.origin has the advantage that successive calls to
\fIsPtCurrent\fR will return the proper position within a window even if the
window was moved between calls.

.bp
Reshapes of a window between successive calls to \fIsPtCurrent\fR are handled
as follows. If the offset of the current screen point from Drect.origin is 
still within the window
after the reshape, \fIsPtCurrent\fR will
return the current screen point within the new window at the same offset from 
Drect.origin that existed in the old window. If the offset from Drect.origin 
is no longer within the window (i.e., the window was reshaped smaller),
\fIsPtCurrent\fR will return Drect.origin as the current screen point.
If an application wants to handle reshape more
elegantly, it can use the following code fragment after each call to the
\fIwait\fR function. This
code fragment will cause the current screen point to move to the upper
left-hand corner of the window after a reshape.
.PP
.RS 3
.ft CM
.nf
if(P->state&RESHAPED) {
	if(!(P->state&MOVED))
		moveto(Drect.origin);
	P->state &= ~(MOVED|RESHAPED);
}
.fi
.ft R
.RE
.PP
The current screen point must be initialized with the
\fImoveto\fR function before \fIsPtCurrent\fR is called the first time.
Library routines which use this facility can check if initialization is
necessary by looking at the global variable \fIdidmoveto\fR each time they
are called. This variable will be set to 0 if \fImoveto\fR has not
been called. An example below shows how the \fIdidmoveto\fR
variable is used to determine if initialization is necessary within a
simple putchar function.
.SH EXAMPLES
There are two types of users of the current screen point. The first
type of user is calling existent library routines such as \fIlprintf\fR
and \fIlputchar\fR, and is only interested in using the
\fImoveto\fR function to control the library routines.
The following code fragment illustrates how \fImoveto\fR can be used
with \fIlprintf\fR to display a prompt at the bottom of the window.
.PP
.RS 3
.ft CM
.nf
.S -2
#include <dmd.h>
#include <font.h>

extern Point fPt();
Point p;

p = fPt( Drect.origin.x,
    Drect.corner.y - FONTHEIGHT(largefont) );
moveto(p);
lprintf("Choose an Option> ");
.fi
.ft R
.S +2
.RE
.bp
.PP
The second type of user of the current screen point is writing
new library routines which use this facility. The following example
shows how to accomplish this by implementing a simple putchar routine.
In the example below, didmoveto is checked first
to see if initialization of the current point is required. Then the code 
obtains
the value of the current screen point, prints a character, and updates
the current screen point for the next call to myputchar.
.PP
.RS 3
.ft CM
.nf
myputchar(c)
char c;
{
	extern int didmoveto;
	extern Point sPtCurrent();
	extern Point string();
	char s[2];
	Point curpos;

	s[0] = c;
	s[1] = '\e0';

	if(!didmoveto)
                moveto(Drect.origin);

	curpos = sPtCurrent();
	curpos = string(&largefont, s, &display,
			curpos, F_STORE);
	moveto(curpos);

}
.fi
.ft R
.RE
.SH SEE ALSO
globals(3R), jmove(3R), lprintf(3L), lputchar(3L),
resources(3R), structures(3R), transform(3R/3L).
.SH BUGS
The \fBdidmoveto\fR initialization scheme will not work with
shared text applications because \fIdidmoveto\fR is a global variable shared
by all invocations of a shared text application. Shared text applications
must explicitly initialize the current screen point by calling
\fImoveto\fR.

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