# ncl_tddtri - Man Page

Draw the triangles defined by a triangle list.

## Synopsis

CALL TDDTRI (RTRI, MTRI, NTRI, ITWK)

## C-Binding Synopsis

#include <ncarg/ncargC.h>

void c_tddtri(float *rtri, int mtri, int *ntri, int *itwk)

## Description

This routine draws the triangles defined by a triangle list. The triangles are drawn in the order specified by the contents of the permutation array ITWK.

The exact manner in which each triangle is drawn depends on the rendering style selected for it. Generally, it is first filled with a user-selected color; if a wire-frame image is desired and no lines are to be considered hidden, this step may be skipped. The fill color can be a specific one chosen by the user (sometimes, it is useful to pick the background color) or one selected from a range of user-specified colors according to the angle between a line from the light source to the center of the triangle and the normal to the plane of the triangle (which results in a shading of the surface). After the triangle is filled, line segments representing its boundary and/or its intersection with planes of constant U, V, and/or W may be drawn in a user-specified contrasting color.

The arguments of TDDTRI are as follows:

- RTRI
(an input array, of type REAL, dimensioned 10 x MTRI) - a list of triangles, probably created by means of calls to TDSTRI, TDITRI, and/or TDMTRI, and sorted, probably by means of a call to TDOTRI.

If you put triangles in the triangle list directly, keep in mind the following: For each value of i from 1 to NTRI, RTRI(1,i), RTRI(2,i), and RTRI(3,i) are the U, V, and W coordinates of the first vertex of the triangle, RTRI(4,i), RTRI(5,i), and RTRI(6,i) are the U, V, and W coordinates of the second vertex of the triangle, RTRI(7,i), RTRI(8,i), and RTRI(9,i) are the U, V, and W coordinates of the third vertex of the triangle, and RTRI(10,i)=REAL(irst), where irst is the index of the desired rendering style array for the triangle. The order of the vertices is meaningful: they must be given in counter-clockwise order as viewed from the "top". It is better if all of the triangles in a triangle list are about the same size.

- MTRI
(an input expression of type INTEGER) - the second dimension of RTRI and thus the maximum number of triangles the triangle list will hold.

- NTRI
(an input expression of type INTEGER) - specifies the number of triangles currently in the list.

- ITWK
(an input array, of type INTEGER, dimensioned at least NTRI) - contains a permutation of the integers from 1 to NTRI (probably generated by calling the routine TDOTRI).

## C-Binding Description

The C-binding argument descriptions are the same as the FORTRAN argument descriptions.

## Access

To use TDDTRI or c_tddtri, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.

## See Also

Online: tdclrs, tdctri, tdgeti, tdgetr, tdgrds, tdgrid, tdgtrs, tdinit, tditri, tdlbla, tdlbls, tdline, tdlnpa, tdmtri, tdotri, tdpack, tdpack_params, tdpara, tdplch, tdprpa, tdprpi, tdprpt, tdseti, tdsetr, tdsort, tdstri, tdstrs

## Copyright

Copyright (C) 1987-2009

University Corporation for Atmospheric Research

The use of this Software is governed by a License Agreement.