1 files changed, 117 insertions, 0 deletions
diff --git a/progs/demos/shadow.c b/progs/demos/shadow.c
new file mode 100644
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+/**
+(c) Copyright 1993, Silicon Graphics, Inc.
+
+ALL RIGHTS RESERVED
+
+Permission to use, copy, modify, and distribute this software
+for any purpose and without fee is hereby granted, provided
+that the above copyright notice appear in all copies and that
+both the copyright notice and this permission notice appear in
+supporting documentation, and that the name of Silicon
+Graphics, Inc. not be used in advertising or publicity
+pertaining to distribution of the software without specific,
+written prior permission.
+
+THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU
+"AS-IS" AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR
+OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF
+MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.  IN NO
+EVENT SHALL SILICON GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE
+ELSE FOR ANY DIRECT, SPECIAL, INCIDENTAL, INDIRECT OR
+CONSEQUENTIAL DAMAGES OF ANY KIND, OR ANY DAMAGES WHATSOEVER,
+INCLUDING WITHOUT LIMITATION, LOSS OF PROFIT, LOSS OF USE,
+SAVINGS OR REVENUE, OR THE CLAIMS OF THIRD PARTIES, WHETHER OR
+NOT SILICON GRAPHICS, INC.  HAS BEEN ADVISED OF THE POSSIBILITY
+OF SUCH LOSS, HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ARISING OUT OF OR IN CONNECTION WITH THE POSSESSION, USE OR
+PERFORMANCE OF THIS SOFTWARE.
+
+US Government Users Restricted Rights
+
+Use, duplication, or disclosure by the Government is subject to
+restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
+(c)(1)(ii) of the Rights in Technical Data and Computer
+Software clause at DFARS 252.227-7013 and/or in similar or
+successor clauses in the FAR or the DOD or NASA FAR
+Supplement.  Unpublished-- rights reserved under the copyright
+laws of the United States.  Contractor/manufacturer is Silicon
+Graphics, Inc., 2011 N.  Shoreline Blvd., Mountain View, CA
+94039-7311.
+
+OpenGL(TM) is a trademark of Silicon Graphics, Inc.
+*/
+
+/* Taken from the projshadow.c - by Tom McReynolds, SGI */
+
+/* Modified by David Bucciarelli */
+
+/* Rendering shadows using projective shadows. */
+
+#include <GL/glut.h>
+
+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])
+{
+  GLfloat vec0[3], vec1[3];
+
+  /* need 2 vectors to find cross product */
+  vec0[X] = v1[X] - v0[X];
+  vec0[Y] = v1[Y] - v0[Y];
+  vec0[Z] = v1[Z] - v0[Z];
+
+  vec1[X] = v2[X] - v0[X];
+  vec1[Y] = v2[Y] - v0[Y];
+  vec1[Z] = v2[Z] - v0[Z];
+
+  /* find cross product to get A, B, and C of plane equation */
+  plane[A] = vec0[Y] * vec1[Z] - vec0[Z] * vec1[Y];
+  plane[B] = -(vec0[X] * vec1[Z] - vec0[Z] * vec1[X]);
+  plane[C] = vec0[X] * vec1[Y] - vec0[Y] * vec1[X];
+
+  plane[D] = -(plane[A] * v0[X] + plane[B] * v0[Y] + plane[C] * v0[Z]);
+}