VDC_EXTENT(3G)

NAME

vdc_extent − defines the logical region of interest (window) for subsequent output primitives.

SYNOPSIS

C SYNTAX

void vdc_extent(fildes,xmin,ymin,zmin,xmax,ymax,zmax);
int fildes;
float xmin,ymin,zmin,xmax,ymax,zmax;

FORTRAN77 SYNTAX

        subroutine vdc_extent(fildes,xmin,ymin,zmin, xmax,ymax,zmax)
        integer*4 fildes
        real xmin,ymin,zmin,xmax,ymax,zmax

PASCAL SYNTAX

procedure vdc_extent(fildes:integer;xmin,ymin,zmin, xmax,ymax,zmax:real);

HP-UX COMPATIBILITY

Level: HP-UX/STANDARD

Origin: ANSI Computer Graphics Interface

DESCRIPTION

INPUT PARAMETERS

fildes
is an integer file descriptor returned by gopen when the I/O path to a graphic device is opened.
xmin,ymin,zmin,xmax,ymax,zmax
respectively define the lower left front and upper right back corners of the Virtual Device Coordinate extent.

DISCUSSION

Vdc_extent defines a logical Cartesian coordinate system used to create a transformation from Virtual Device Coordinates to physical device coordinates.

This coordinate system establishes the sense and orientation of the Virtual Device Coordinate extent. That is, the directions of the positive x-axis and positive y-axis and whether the positive y-axis is 90 degrees clock-wise or 90 degrees counter-clock-wise from the positive x-axis. This also establishes the direction of positive and negative angles. Positive angles are measured in the direction from the positive x-axis to the positive y-axis.

The meanings of up, down, right, left, front and back are also defined. Up is associated with the positive x-axis, down with the negative x-axis, right with the positive y-axis, and left with the negative y-axis. A positive z-axis is back and a negative z-axis is the front of the picture.

Specification of values outside the vdc extent area is permitted. It is intended that the visible portion of the image be contained within the extent area, however. For example, the center of a circle may be outside the extent area. The extent area is intended to provide a frame for the region of interest in a picture.

The actual clipping bounds must be a subset of the vdc system. Thus, the clipping bounds may be truncated if necessary.

With the settings of the other coordinate system parameters, the vdc extent uses as much of the physical region of interest as possible without distorting the image or eliminating any part of the image within the range of the extent. See set_p1_p2, mapping_mode and viewport_justification for ways to modify this mapping.

If the extent values are set to be equal to the device units of the graphic device, no transformation occurs making the process more efficient.

If one or more dimensions for the extent equal zero, an error is generated and the vdc extent is not changed.

This procedure updates the current vdc-to-device units transformation matrix. This means the matrix at the bottom of the matrix stack is changed. No other matrices in the matrix stack are altered.

Changes to vdc extent may not effect previously set values such as text size or tracking relationships. Vdc extent should be set before setting related values.

Beware: If the clip_level is CLIP_TO_RECT which is the default case (see clip_indicator) then when changing vdc_extent make sure clip_rectangle is changed as well or all output primitives may get clipped to a very small area.

DEFAULTS

(Xmin,ymin,zmin,xmax,ymax,zmax) = (0.0,0.0,0.0,1.0,1.0,1.0)

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