1 /* Copyright 1988, Brown Computer Graphics Group. All Rights Reserved. */
3 /* --------------------------------------------------------------------------
4 * This file contains routines that operate on matrices and vectors, or
6 * -------------------------------------------------------------------------*/
8 /* #include "sphigslocal.h" */
10 /* -------------------------- Static Routines ---------------------------- */
12 /* ------------------------- Internal Routines --------------------------- */
14 /* -------------------------- Public Routines ---------------------------- */
17 * Multiplies a vector by a matrix, setting the result vector.
18 * It assumes all homogeneous coordinates are 1.
19 * The two vectors involved may be the same.
34 MAT3mult_vec(result_vec, vec, mat)
40 register double *temp = tempvec;
42 temp[0] = vec[0] * mat[0][0] + vec[1] * mat[1][0] +
43 vec[2] * mat[2][0] + mat[3][0];
44 temp[1] = vec[0] * mat[0][1] + vec[1] * mat[1][1] +
45 vec[2] * mat[2][1] + mat[3][1];
46 temp[2] = vec[0] * mat[0][2] + vec[1] * mat[1][2] +
47 vec[2] * mat[2][2] + mat[3][2];
49 MAT3_COPY_VEC(result_vec, temp);
53 * Multiplies a vector of size 4 by a matrix, setting the result vector.
54 * The fourth element of the vector is the homogeneous coordinate, which
55 * may or may not be 1. If the "normalize" parameter is TRUE, then the
56 * result vector will be normalized so that the homogeneous coordinate is 1.
57 * The two vectors involved may be the same.
58 * This returns zero if the vector was to be normalized, but couldn't be.
62 MAT3mult_hvec(result_vec, vec, mat, normalize)
64 register MAT3hvec vec;
69 register double *temp = tempvec;
70 register int ret = TRUE;
72 temp[0] = vec[0] * mat[0][0] + vec[1] * mat[1][0] +
73 vec[2] * mat[2][0] + vec[3] * mat[3][0];
74 temp[1] = vec[0] * mat[0][1] + vec[1] * mat[1][1] +
75 vec[2] * mat[2][1] + vec[3] * mat[3][1];
76 temp[2] = vec[0] * mat[0][2] + vec[1] * mat[1][2] +
77 vec[2] * mat[2][2] + vec[3] * mat[3][2];
78 temp[3] = vec[0] * mat[0][3] + vec[1] * mat[1][3] +
79 vec[2] * mat[2][3] + vec[3] * mat[3][3];
81 /* Normalize if asked for, possible, and necessary */
83 if (MAT3_IS_ZERO(temp[3])) {
86 "Can't normalize vector: homogeneous coordinate is 0");
91 norm_fac = 1.0 / temp[3];
92 MAT3_SCALE_VEC(result_vec, temp, norm_fac);
96 else MAT3_COPY_HVEC(result_vec, temp);
102 * Sets the first vector to be the cross-product of the last two vectors.
106 MAT3cross_product(result_vec, vec1, vec2)
108 register MAT3vec vec1, vec2;
111 register double *temp = tempvec;
113 temp[0] = vec1[1] * vec2[2] - vec1[2] * vec2[1];
114 temp[1] = vec1[2] * vec2[0] - vec1[0] * vec2[2];
115 temp[2] = vec1[0] * vec2[1] - vec1[1] * vec2[0];
117 MAT3_COPY_VEC(result_vec, temp);
121 * Finds a vector perpendicular to vec and stores it in result_vec.
122 * Method: take any vector (we use <0,1,0>) and subtract the
123 * portion of it pointing in the vec direction. This doesn't
124 * work if vec IS <0,1,0> or is very near it. So if this is
125 * the case, use <0,0,1> instead.
126 * If "is_unit" is TRUE, the given vector is assumed to be unit length.
129 #define SELECT .7071 /* selection constant (roughly .5*sqrt(2) */
132 MAT3perp_vec(result_vec, vec, is_unit)
133 MAT3vec result_vec, vec;
139 MAT3_SET_VEC(result_vec, 0.0, 1.0, 0.0);
141 MAT3_COPY_VEC(norm, vec);
143 if (! is_unit) MAT3_NORMALIZE_VEC(norm, dot);
145 /* See if vector is too close to <0,1,0>. If so, use <0,0,1> */
146 if ((dot = MAT3_DOT_PRODUCT(norm, result_vec)) > SELECT || dot < -SELECT) {
149 dot = MAT3_DOT_PRODUCT(norm, result_vec);
152 /* Subtract off non-perpendicular part */
153 result_vec[0] -= dot * norm[0];
154 result_vec[1] -= dot * norm[1];
155 result_vec[2] -= dot * norm[2];
157 /* Make result unit length */
158 MAT3_NORMALIZE_VEC(result_vec, dot);