+
+
+/******************** begin shadow code ********************/
+
+/* Taken from the projshadow.c - by Tom McReynolds, SGI */
+
+/* Modified by David Bucciarelli */
+
+enum {
+ X, Y, Z, W
+};
+enum {
+ A, B, C, D
+};
+
+/* create a matrix that will project the desired shadow */
+void
+shadowmatrix(GLfloat shadowMat[4][4],
+ GLfloat groundplane[4],
+ GLfloat lightpos[4])
+{
+ GLfloat dot;
+
+ /* find dot product between light position vector and ground plane normal */
+ dot = groundplane[X] * lightpos[X] +
+ groundplane[Y] * lightpos[Y] +
+ groundplane[Z] * lightpos[Z] +
+ groundplane[W] * lightpos[W];
+
+ shadowMat[0][0] = dot - lightpos[X] * groundplane[X];
+ shadowMat[1][0] = 0.f - lightpos[X] * groundplane[Y];
+ shadowMat[2][0] = 0.f - lightpos[X] * groundplane[Z];
+ shadowMat[3][0] = 0.f - lightpos[X] * groundplane[W];
+
+ shadowMat[X][1] = 0.f - lightpos[Y] * groundplane[X];
+ shadowMat[1][1] = dot - lightpos[Y] * groundplane[Y];
+ shadowMat[2][1] = 0.f - lightpos[Y] * groundplane[Z];
+ shadowMat[3][1] = 0.f - lightpos[Y] * groundplane[W];
+
+ shadowMat[X][2] = 0.f - lightpos[Z] * groundplane[X];
+ shadowMat[1][2] = 0.f - lightpos[Z] * groundplane[Y];
+ shadowMat[2][2] = dot - lightpos[Z] * groundplane[Z];
+ shadowMat[3][2] = 0.f - lightpos[Z] * groundplane[W];
+
+ shadowMat[X][3] = 0.f - lightpos[W] * groundplane[X];
+ shadowMat[1][3] = 0.f - lightpos[W] * groundplane[Y];
+ shadowMat[2][3] = 0.f - lightpos[W] * groundplane[Z];
+ shadowMat[3][3] = dot - lightpos[W] * groundplane[W];
+
+}
+
+/* find the plane equation given 3 points */
+void
+findplane(GLfloat plane[4],
+ GLfloat v0[3], GLfloat v1[3], GLfloat v2[3])