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The graPHIGS Programming Interface : Subroutine Reference

GPEVM2 - Evaluate View Mapping Matrix 2

GPEVM2 (window, viewpt, errind, matrix)

Purpose

Use GPEVM2 to create a view mapping matrix. The matrix can be used as input to the Set Extended View Representation (GPXVR) subroutine. This subroutine returns a two-dimensional matrix.

The calculation of the view mapping matrix is as follows:

  • The z extents for the viewport are set to the z extents of the NPC range.

  • The projection type is set to 1=PARALLEL

  • The projection reference point is placed on a line perpendicular to the center of the specified window. The z value of the projection reference point is set to one-half of the maximum of the Umax-Umin and Vmax-Vmin.

  • The view plane distance is set to zero.

  • The far clipping plane is set to the negative of one-half of the maximum of the Umax-Umin and Vmax-Vmin.

  • The near clipping plane is set to one-half of the maximum of the Umax-Umin and Vmax-Vmin.

    • If the view mapping matrix can be computed, the error indicator is set to zero, and the matrix is returned. If the matrix cannot be computed, the error indicator contains an error number indicating the reason. In this case, the value of the output parameter is unpredictable.

    Parameters

    window -- specified by user, 4 short floating-point numbers (VC)

    Window limits (Umin, Umax, Vmin, Vmax)

    viewpt -- specified by user, 4 short floating-point numbers (NPC)

    Viewport limits (Xmin, Xmax, Ymin, Ymax)

    errind -- returned by the graPHIGS API, fullword integer

    Error indicator. If the error indicator is zero, the request has been completed. Otherwise, one of the following errors exists:
    44
    INVALID WINDOW DEFINITION
    330
    INVALID VIEWPORT

    matrix -- returned by the graPHIGS API, 9 short floating-point numbers

    View mapping matrix. For the output view matrix, the elements are in the following order: 
                     
    |m11  m12  m13|
    |m21  m22  m23| --->(m11,m12,m13,m21.....m43)
    |m41  m42  m43|

    Error Codes

    None

    Related Subroutines

    GPXVR
    Set Extended View Representation

    RCP code

    201331208 (X'0C001208')

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