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.\" $XConsortium: p389,v 5.2 94/04/17 20:59:00 rws Exp $
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$XMCOPY
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.TH "SET WORKSTATION VIEWPORT" 3P "29 February 1991"
.SH NAME
SET WORKSTATION VIEWPORT  \- set 2D viewport limits for a specified workstation
.IX "Workstation Transformation" "SET WORKSTATION VIEWPORT"
.SH SYNOPSIS
.SS C Syntax
.ft B
.ta 1.5i 3.25i
.nf
void
pset_ws_vp ( ws, viewport )
Pint	ws;	\fIworkstation id\fP
Plimit	*viewport;	\fIworkstation viewport limits\fP
.fi
.ft R
.SS Required PHIGS Operating States
(PHOP, WSOP, *, *)
.SH DESCRIPTION
.SS Purpose
\s-2SET WORKSTATION VIEWPORT\s+2
defines a 2D area in Device Coordinate (\s-2DC\s+2) space, at a constant \fIz\fP value.  
The abstract image within the workstation window, defined in Normalized
Projection Coordinate (\s-2NPC\s+2) space, is mapped to this viewport.  
.LP
Together, the workstation window and the workstation viewport
define the \fIworkstation transformation\fP that converts the image
from \s-2NPC\s+2 to \s-2DC\s+2 of workstation's physical display surface.  The
workstation window defines what within \s-2NPC\s+2 space is displayed;  the
workstation viewport defines where the image is displayed in \s-2DC\s+2
space.  
.LP
Control of the workstation transformation allows you to choose
a portion of the abstract image
composed in \s-2NPC\s+2 space for display on the workstation,
without changing the definition of the image in \s-2NPC\s+2 space.  
.SS C Input Parameters
.IP \fIws\fP
The identifier of the workstation for which the viewport is to be set.  
.IP \fIviewport\fP
A pointer to a structure containing the \s-2DC\s+2 limits for the
\s-2\&2D\s+2 workstation viewport, defined as follows:
.nf
.ta .5i +\w'Pfloat     'u +\w'x_max;     'u
.sp .4
typedef struct  {
.sp .2
	Pfloat	x_min;	/* x minimum */
	Pfloat	x_max;	/* x maximum */
	Pfloat	y_min;	/* y minimum */
	Pfloat	y_max;	/* y maximum */
.sp .2
} Plimit;
.fi
.SS Execution
.LP
The current workstation viewport defines the area in Device Coordinates in
which the abstract image within the current workstation window is displayed.  
The workstation window is defined in Normalized Projection Coordinates.  
Together, the workstation window and the workstation viewport
define the \fIworkstation transformation\fP that converts the image
from \s-2NPC\s+2 to \s-2DC\s+2 of workstation's physical display surface.  
.LP
The \fIx\fP minimum must be non-negative and less than \fIx\fP 
maximum and \fIy\fP minimum must be non-negative and less than 
\fIy\fP maximum.  
In addition, all values must be within the workstation's \s-2DC\s+2 range.  
The default \s-2PEX-SI\s0 workstation \s-2DC\s+2 maximum is 1, 
but it is selectable by using \s-2WORKSTATION TYPE SET (3P)\s+2. 
.LP
\s-2SET WORKSTATION VIEWPORT\s+2 sets the \fIx\fP and \fIy\fP
components of the requested workstation viewport in the specified
workstation's state list to the values specified.  The
\fIz\fP component of the requested workstation viewport and current
workstation viewport are not changed.  
The effect of calling \s-2SET WORKSTATION VIEWPORT\s+2 is visible
only after the requested workstation viewport replaces the 
current workstation viewport.  
The time at which this occurs
depends on the workstation's display update state.  
This action is performed immediately,
and the workstation transformation update state is set to \s-2NOTPENDING\s+2,
if any one of the following is true:  
.sp .5v
.in +0.5i
.ta +0.2i
.ti -0.2i
\(bu	The workstation's display update state allows update.  
.sp .5v
.ti -0.2i
\(bu	The workstation's modification mode is any value other than
No Immediate Visual Effect,
and the dynamic modification accepted for workstation transformation
entry in the workstation description table is set to Immediate.  
.sp .5v
.ti -0.2i
\(bu	The display space empty status in the workstation state list
is \s-2EMPTY\s+2.
.LP
Otherwise,
the workstation transformation update state is set to \s-2PENDING\s+2,
and the requested workstation viewport will not replace
the current workstation viewport until
the next time the workstation is updated.  
The workstation transformation update state will be set to \s-2NOTPENDING\s+2
at that time.  
.LP
If the current workstation window and viewport do not have the same aspect
ratios, the workstation transformation preserves the proportions of the
image by mapping the workstation window to the largest possible area of the
workstation viewport so that: 
.sp .5v
.in +0.5i
.ta +0.2i
.ti -0.2i
\(bu	The aspect ratio of the window in \fIx\fP
and \fIy\fP is maintained.
.sp .5v
.ti -0.2i
\(bu	The lower left hand corner of the window is mapped to the lower left
hand corner of the viewport.  
.LP
If the aspect ratios of the workstation window and viewport are different,
there will be unused space along the upper or
right-hand edges of the viewport, but not both.
.LP
The default workstation transformation maps the entire \s-2NPC\s+2 view plane,
[0,1] \(mu [0,1] \(mu [0,1], onto the largest square area in the
workstation display space including the display's lower left corner.  
.\"different:	The workstation transformation can be changed at any time after
.\"different:	the workstation is opened. However, changing the transformation
.\"different:	may cause an implicit regeneration of the picture regardless of
.\"different:	the explicit setting of the workstation's display update state.
.LP
.SH ERRORS
.IP 003
Ignoring function, function requires state (\s-2PHOP\s+2, \s-2WSOP\s+2, \s-2*\s+2, \s-2*\s+2)
.IP 054
Ignoring function, the specified workstation is not open
.IP 057
Ignoring function, specified workstation is of category \s-2MI\s+2
.IP 152
Ignoring function, invalid viewport;
\s-2XMIN \(>= XMAX\s+2 or \s-2YMIN \(>= YMAX\s+2.
.IP 157
Ignoring function, the workstation viewport is not within display space
.SH SEE ALSO
.nf
.IP
.ta 0.5i
.SM "SET WORKSTATION WINDOW (3P)"
.SM "SET WORKSTATION VIEWPORT 3 (3P)"
.fi
