progs/demos/shadow.c

   1 /**
   2 (c) Copyright 1993, Silicon Graphics, Inc.
   3
   4 ALL RIGHTS RESERVED
   5
   6 Permission to use, copy, modify, and distribute this software
   7 for any purpose and without fee is hereby granted, provided
   8 that the above copyright notice appear in all copies and that
   9 both the copyright notice and this permission notice appear in
  10 supporting documentation, and that the name of Silicon
  11 Graphics, Inc. not be used in advertising or publicity
  12 pertaining to distribution of the software without specific,
  13 written prior permission.
  14
  15 THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU
  16 "AS-IS" AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR
  17 OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF
  18 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.  IN NO
  19 EVENT SHALL SILICON GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE
  20 ELSE FOR ANY DIRECT, SPECIAL, INCIDENTAL, INDIRECT OR
  21 CONSEQUENTIAL DAMAGES OF ANY KIND, OR ANY DAMAGES WHATSOEVER,
  22 INCLUDING WITHOUT LIMITATION, LOSS OF PROFIT, LOSS OF USE,
  23 SAVINGS OR REVENUE, OR THE CLAIMS OF THIRD PARTIES, WHETHER OR
  24 NOT SILICON GRAPHICS, INC.  HAS BEEN ADVISED OF THE POSSIBILITY
  25 OF SUCH LOSS, HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  26 ARISING OUT OF OR IN CONNECTION WITH THE POSSESSION, USE OR
  27 PERFORMANCE OF THIS SOFTWARE.
  28
  29 US Government Users Restricted Rights
  30
  31 Use, duplication, or disclosure by the Government is subject to
  32 restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
  33 (c)(1)(ii) of the Rights in Technical Data and Computer
  34 Software clause at DFARS 252.227-7013 and/or in similar or
  35 successor clauses in the FAR or the DOD or NASA FAR
  36 Supplement.  Unpublished-- rights reserved under the copyright
  37 laws of the United States.  Contractor/manufacturer is Silicon
  38 Graphics, Inc., 2011 N.  Shoreline Blvd., Mountain View, CA
  39 94039-7311.
  40
  41 OpenGL(TM) is a trademark of Silicon Graphics, Inc.
  42 */
  43
  44 /* Taken from the projshadow.c - by Tom McReynolds, SGI */
  45
  46 /* Modified by David Bucciarelli */
  47
  48 /* Rendering shadows using projective shadows. */
  49
  50 #include <GL/glut.h>
  51 #include "shadow.h"
  52
  53
  54 enum {
  55   X, Y, Z, W
  56 };
  57 enum {
  58   A, B, C, D
  59 };
  60
  61 /* create a matrix that will project the desired shadow */
  62 void
  63 shadowmatrix(GLfloat shadowMat[4][4],
  64   GLfloat groundplane[4],
  65   GLfloat lightpos[4])
  66 {
  67   GLfloat dot;
  68
  69   /* find dot product between light position vector and ground plane normal */
  70   dot = groundplane[X] * lightpos[X] +
  71     groundplane[Y] * lightpos[Y] +
  72     groundplane[Z] * lightpos[Z] +
  73     groundplane[W] * lightpos[W];
  74
  75   shadowMat[0][0] = dot - lightpos[X] * groundplane[X];
  76   shadowMat[1][0] = 0.f - lightpos[X] * groundplane[Y];
  77   shadowMat[2][0] = 0.f - lightpos[X] * groundplane[Z];
  78   shadowMat[3][0] = 0.f - lightpos[X] * groundplane[W];
  79
  80   shadowMat[X][1] = 0.f - lightpos[Y] * groundplane[X];
  81   shadowMat[1][1] = dot - lightpos[Y] * groundplane[Y];
  82   shadowMat[2][1] = 0.f - lightpos[Y] * groundplane[Z];
  83   shadowMat[3][1] = 0.f - lightpos[Y] * groundplane[W];
  84
  85   shadowMat[X][2] = 0.f - lightpos[Z] * groundplane[X];
  86   shadowMat[1][2] = 0.f - lightpos[Z] * groundplane[Y];
  87   shadowMat[2][2] = dot - lightpos[Z] * groundplane[Z];
  88   shadowMat[3][2] = 0.f - lightpos[Z] * groundplane[W];
  89
  90   shadowMat[X][3] = 0.f - lightpos[W] * groundplane[X];
  91   shadowMat[1][3] = 0.f - lightpos[W] * groundplane[Y];
  92   shadowMat[2][3] = 0.f - lightpos[W] * groundplane[Z];
  93   shadowMat[3][3] = dot - lightpos[W] * groundplane[W];
  94
  95 }
  96
  97 /* find the plane equation given 3 points */
  98 void
  99 findplane(GLfloat plane[4],
 100   GLfloat v0[3], GLfloat v1[3], GLfloat v2[3])
 101 {
 102   GLfloat vec0[3], vec1[3];
 103
 104   /* need 2 vectors to find cross product */
 105   vec0[X] = v1[X] - v0[X];
 106   vec0[Y] = v1[Y] - v0[Y];
 107   vec0[Z] = v1[Z] - v0[Z];
 108
 109   vec1[X] = v2[X] - v0[X];
 110   vec1[Y] = v2[Y] - v0[Y];
 111   vec1[Z] = v2[Z] - v0[Z];
 112
 113   /* find cross product to get A, B, and C of plane equation */
 114   plane[A] = vec0[Y] * vec1[Z] - vec0[Z] * vec1[Y];
 115   plane[B] = -(vec0[X] * vec1[Z] - vec0[Z] * vec1[X]);
 116   plane[C] = vec0[X] * vec1[Y] - vec0[Y] * vec1[X];
 117
 118   plane[D] = -(plane[A] * v0[X] + plane[B] * v0[Y] + plane[C] * v0[Z]);
 119 }