
/* projtex.c - by David Yu and David Blythe, SGI */

/**
 ** Demonstrates simple projective texture mapping.
 **
 ** Button1 changes view, Button2 moves texture.
 **
 ** (See: Segal, Korobkin, van Widenfelt, Foran, and Haeberli
 **  "Fast Shadows and Lighting Effects Using Texture Mapping", SIGGRAPH '92)
 **
 ** 1994,1995 -- David G Yu
 **
 ** cc -o projtex projtex.c texture.c -lglut -lGLU -lGL -lX11 -lm
 **/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <GL/glut.h>
#include "texture.h"

/* Some <math.h> files do not define M_PI... */
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

int winWidth, winHeight;

GLboolean redrawContinuously = GL_FALSE;

float angle, axis[3];
enum MoveModes {
  MoveNone, MoveView, MoveObject, MoveTexture
};
enum MoveModes mode = MoveNone;

GLfloat objectXform[4][4];
GLfloat textureXform[4][4];

void (*drawObject) (void);
void (*loadTexture) (void);
GLboolean textureEnabled = GL_TRUE;
GLboolean showProjection = GL_TRUE;
GLboolean linearFilter = GL_TRUE;

char *texFilename = NULL;

GLfloat zoomFactor = 1.0;

/*****************************************************************/

/* matrix = identity */
void
matrixIdentity(GLfloat matrix[16])
{
  matrix[0] = 1.0;
  matrix[1] = 0.0;
  matrix[2] = 0.0;
  matrix[3] = 0.0;
  matrix[4] = 0.0;
  matrix[5] = 1.0;
  matrix[6] = 0.0;
  matrix[7] = 0.0;
  matrix[8] = 0.0;
  matrix[9] = 0.0;
  matrix[10] = 1.0;
  matrix[11] = 0.0;
  matrix[12] = 0.0;
  matrix[13] = 0.0;
  matrix[14] = 0.0;
  matrix[15] = 1.0;
}

/* matrix2 = transpose(matrix1) */
void
matrixTranspose(GLfloat matrix2[16], GLfloat matrix1[16])
{
  matrix2[0] = matrix1[0];
  matrix2[1] = matrix1[4];
  matrix2[2] = matrix1[8];
  matrix2[3] = matrix1[12];

  matrix2[4] = matrix1[1];
  matrix2[5] = matrix1[5];
  matrix2[6] = matrix1[9];
  matrix2[7] = matrix1[13];

  matrix2[8] = matrix1[2];
  matrix2[9] = matrix1[6];
  matrix2[10] = matrix1[10];
  matrix2[11] = matrix1[14];

  matrix2[12] = matrix1[3];
  matrix2[13] = matrix1[7];
  matrix2[14] = matrix1[14];
  matrix2[15] = matrix1[15];
}

/*****************************************************************/

/* load SGI .rgb image (pad with a border of the specified width and color) */
static void
imgLoad(char *filenameIn, int borderIn, GLfloat borderColorIn[4],
  int *wOut, int *hOut, GLubyte ** imgOut)
{
  int border = borderIn;
  int width, height;
  int w, h;
  GLubyte *image, *img, *p;
  int i, j, components;

  image = (GLubyte *) read_texture(filenameIn, &width, &height, &components);
  w = width + 2 * border;
  h = height + 2 * border;
  img = (GLubyte *) calloc(w * h, 4 * sizeof(unsigned char));

  p = img;
  for (j = -border; j < height + border; ++j) {
    for (i = -border; i < width + border; ++i) {
      if (0 <= j && j <= height - 1 && 0 <= i && i <= width - 1) {
        p[0] = image[4 * (j * width + i) + 0];
        p[1] = image[4 * (j * width + i) + 1];
        p[2] = image[4 * (j * width + i) + 2];
        p[3] = 0xff;
      } else {
        p[0] = borderColorIn[0] * 0xff;
        p[1] = borderColorIn[1] * 0xff;
        p[2] = borderColorIn[2] * 0xff;
        p[3] = borderColorIn[3] * 0xff;
      }
      p += 4;
    }
  }
  free(image);
  *wOut = w;
  *hOut = h;
  *imgOut = img;
}

/*****************************************************************/

/* Load the image file specified on the command line as the current texture */
void
loadImageTexture(void)
{
  static int texWidth, texHeight;
  static GLubyte *texData;
  GLfloat borderColor[4] =
  {1.0, 1.0, 1.0, 1.0};

  if (!texData && texFilename) {
    imgLoad(texFilename, 2, borderColor, &texWidth, &texHeight, &texData);
  }
  if (linearFilter) {
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  } else {
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  }
  glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, borderColor);
  gluBuild2DMipmaps(GL_TEXTURE_2D, 4, texWidth, texHeight,
    GL_RGBA, GL_UNSIGNED_BYTE, texData);
}

/* Create a simple spotlight pattern and make it the current texture */
void
loadSpotlightTexture(void)
{
  static int texWidth = 64, texHeight = 64;
  static GLubyte *texData;
  GLfloat borderColor[4] =
  {0.1, 0.1, 0.1, 1.0};

  if (!texData) {
    GLubyte *p;
    int i, j;

    texData = (GLubyte *) malloc(texWidth * texHeight * 4 * sizeof(GLubyte));

    p = texData;
    for (j = 0; j < texHeight; ++j) {
      float dy = (texHeight * 0.5 - j + 0.5) / (texHeight * 0.5);

      for (i = 0; i < texWidth; ++i) {
        float dx = (texWidth * 0.5 - i + 0.5) / (texWidth * 0.5);
        float r = cos(M_PI / 2.0 * sqrt(dx * dx + dy * dy));
        float c;

        r = (r < 0) ? 0 : r * r;
        c = 0xff * (r + borderColor[0]);
        p[0] = (c <= 0xff) ? c : 0xff;
        c = 0xff * (r + borderColor[1]);
        p[1] = (c <= 0xff) ? c : 0xff;
        c = 0xff * (r + borderColor[2]);
        p[2] = (c <= 0xff) ? c : 0xff;
        c = 0xff * (r + borderColor[3]);
        p[3] = (c <= 0xff) ? c : 0xff;
        p += 4;
      }
    }
  }
  if (linearFilter) {
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  } else {
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  }
  glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, borderColor);
  gluBuild2DMipmaps(GL_TEXTURE_2D, 4, texWidth, texHeight,
    GL_RGBA, GL_UNSIGNED_BYTE, texData);
}

/*****************************************************************/

void
checkErrors(void)
{
  GLenum error;
  while ((error = glGetError()) != GL_NO_ERROR) {
    fprintf(stderr, "Error: %s\n", (char *) gluErrorString(error));
  }
}

void
drawCube(void)
{
  glBegin(GL_QUADS);

  glNormal3f(-1.0, 0.0, 0.0);
  glColor3f(0.80, 0.50, 0.50);
  glVertex3f(-0.5, -0.5, -0.5);
  glVertex3f(-0.5, -0.5, 0.5);
  glVertex3f(-0.5, 0.5, 0.5);
  glVertex3f(-0.5, 0.5, -0.5);

  glNormal3f(1.0, 0.0, 0.0);
  glColor3f(0.50, 0.80, 0.50);
  glVertex3f(0.5, 0.5, 0.5);
  glVertex3f(0.5, -0.5, 0.5);
  glVertex3f(0.5, -0.5, -0.5);
  glVertex3f(0.5, 0.5, -0.5);

  glNormal3f(0.0, -1.0, 0.0);
  glColor3f(0.50, 0.50, 0.80);
  glVertex3f(-0.5, -0.5, -0.5);
  glVertex3f(0.5, -0.5, -0.5);
  glVertex3f(0.5, -0.5, 0.5);
  glVertex3f(-0.5, -0.5, 0.5);

  glNormal3f(0.0, 1.0, 0.0);
  glColor3f(0.50, 0.80, 0.80);
  glVertex3f(0.5, 0.5, 0.5);
  glVertex3f(0.5, 0.5, -0.5);
  glVertex3f(-0.5, 0.5, -0.5);
  glVertex3f(-0.5, 0.5, 0.5);

  glNormal3f(0.0, 0.0, -1.0);
  glColor3f(0.80, 0.50, 0.80);
  glVertex3f(-0.5, -0.5, -0.5);
  glVertex3f(-0.5, 0.5, -0.5);
  glVertex3f(0.5, 0.5, -0.5);
  glVertex3f(0.5, -0.5, -0.5);

  glNormal3f(0.0, 0.0, 1.0);
  glColor3f(1.00, 0.80, 0.50);
  glVertex3f(0.5, 0.5, 0.5);
  glVertex3f(-0.5, 0.5, 0.5);
  glVertex3f(-0.5, -0.5, 0.5);
  glVertex3f(0.5, -0.5, 0.5);
  glEnd();
}

void
drawDodecahedron(void)
{
#define A (0.5 * 1.61803)  /* (sqrt(5) + 1) / 2 */
#define B (0.5 * 0.61803)  /* (sqrt(5) - 1) / 2 */
#define C (0.5 * 1.0)
  GLfloat vertexes[20][3] =
  {
    {-A, 0.0, B},
    {-A, 0.0, -B},
    {A, 0.0, -B},
    {A, 0.0, B},
    {B, -A, 0.0},
    {-B, -A, 0.0},
    {-B, A, 0.0},
    {B, A, 0.0},
    {0.0, B, -A},
    {0.0, -B, -A},
    {0.0, -B, A},
    {0.0, B, A},
    {-C, -C, C},
    {-C, -C, -C},
    {C, -C, -C},
    {C, -C, C},
    {-C, C, C},
    {-C, C, -C},
    {C, C, -C},
    {C, C, C},
  };
#undef A
#undef B
#undef C
  GLint polygons[12][5] =
  {
    {0, 12, 10, 11, 16},
    {1, 17, 8, 9, 13},
    {2, 14, 9, 8, 18},
    {3, 19, 11, 10, 15},
    {4, 14, 2, 3, 15},
    {5, 12, 0, 1, 13},
    {6, 17, 1, 0, 16},
    {7, 19, 3, 2, 18},
    {8, 17, 6, 7, 18},
    {9, 14, 4, 5, 13},
    {10, 12, 5, 4, 15},
    {11, 19, 7, 6, 16},
  };
  int i;

  glColor3f(0.75, 0.75, 0.75);
  for (i = 0; i < 12; ++i) {
    GLfloat *p0, *p1, *p2, d;
    GLfloat u[3], v[3], n[3];

    p0 = &vertexes[polygons[i][0]][0];
    p1 = &vertexes[polygons[i][1]][0];
    p2 = &vertexes[polygons[i][2]][0];

    u[0] = p2[0] - p1[0];
    u[1] = p2[1] - p1[1];
    u[2] = p2[2] - p1[2];

    v[0] = p0[0] - p1[0];
    v[1] = p0[1] - p1[1];
    v[2] = p0[2] - p1[2];

    n[0] = u[1] * v[2] - u[2] * v[1];
    n[1] = u[2] * v[0] - u[0] * v[2];
    n[2] = u[0] * v[1] - u[1] * v[0];

    d = 1.0 / sqrt(n[0] * n[0] + n[1] * n[1] + n[2] * n[2]);
    n[0] *= d;
    n[1] *= d;
    n[2] *= d;

    glBegin(GL_POLYGON);
    glNormal3fv(n);
    glVertex3fv(p0);
    glVertex3fv(p1);
    glVertex3fv(p2);
    glVertex3fv(vertexes[polygons[i][3]]);
    glVertex3fv(vertexes[polygons[i][4]]);
    glEnd();
  }
}

void
drawSphere(void)
{
  int numMajor = 24;
  int numMinor = 32;
  float radius = 0.8;
  double majorStep = (M_PI / numMajor);
  double minorStep = (2.0 * M_PI / numMinor);
  int i, j;

  glColor3f(0.50, 0.50, 0.50);
  for (i = 0; i < numMajor; ++i) {
    double a = i * majorStep;
    double b = a + majorStep;
    double r0 = radius * sin(a);
    double r1 = radius * sin(b);
    GLfloat z0 = radius * cos(a);
    GLfloat z1 = radius * cos(b);

    glBegin(GL_TRIANGLE_STRIP);
    for (j = 0; j <= numMinor; ++j) {
      double c = j * minorStep;
      GLfloat x = cos(c);
      GLfloat y = sin(c);

      glNormal3f((x * r0) / radius, (y * r0) / radius, z0 / radius);
      glTexCoord2f(j / (GLfloat) numMinor, i / (GLfloat) numMajor);
      glVertex3f(x * r0, y * r0, z0);

      glNormal3f((x * r1) / radius, (y * r1) / radius, z1 / radius);
      glTexCoord2f(j / (GLfloat) numMinor, (i + 1) / (GLfloat) numMajor);
      glVertex3f(x * r1, y * r1, z1);
    }
    glEnd();
  }
}

/*****************************************************************/

float xmin = -0.035, xmax = 0.035;
float ymin = -0.035, ymax = 0.035;
float nnear = 0.1;
float ffar = 1.9;
float distance = -1.0;

static void
loadTextureProjection(GLfloat m[16])
{
  GLfloat mInverse[4][4];

  /* Should use true inverse, but since m consists only of rotations, we can
     just use the transpose. */
  matrixTranspose((GLfloat *) mInverse, m);

  glMatrixMode(GL_TEXTURE);
  glLoadIdentity();
  glTranslatef(0.5, 0.5, 0.0);
  glScalef(0.5, 0.5, 1.0);
  glFrustum(xmin, xmax, ymin, ymax, nnear, ffar);
  glTranslatef(0.0, 0.0, distance);
  glMultMatrixf((GLfloat *) mInverse);
  glMatrixMode(GL_MODELVIEW);
}

static void
drawTextureProjection(void)
{
  float t = ffar / nnear;
  GLfloat n[4][3];
  GLfloat f[4][3];

  n[0][0] = xmin;
  n[0][1] = ymin;
  n[0][2] = -(nnear + distance);

  n[1][0] = xmax;
  n[1][1] = ymin;
  n[1][2] = -(nnear + distance);

  n[2][0] = xmax;
  n[2][1] = ymax;
  n[2][2] = -(nnear + distance);

  n[3][0] = xmin;
  n[3][1] = ymax;
  n[3][2] = -(nnear + distance);

  f[0][0] = xmin * t;
  f[0][1] = ymin * t;
  f[0][2] = -(ffar + distance);

  f[1][0] = xmax * t;
  f[1][1] = ymin * t;
  f[1][2] = -(ffar + distance);

  f[2][0] = xmax * t;
  f[2][1] = ymax * t;
  f[2][2] = -(ffar + distance);

  f[3][0] = xmin * t;
  f[3][1] = ymax * t;
  f[3][2] = -(ffar + distance);

  glColor3f(1.0, 1.0, 0.0);
  glBegin(GL_LINE_LOOP);
  glVertex3fv(n[0]);
  glVertex3fv(n[1]);
  glVertex3fv(n[2]);
  glVertex3fv(n[3]);
  glVertex3fv(f[3]);
  glVertex3fv(f[2]);
  glVertex3fv(f[1]);
  glVertex3fv(f[0]);
  glVertex3fv(n[0]);
  glVertex3fv(n[1]);
  glVertex3fv(f[1]);
  glVertex3fv(f[0]);
  glVertex3fv(f[3]);
  glVertex3fv(f[2]);
  glVertex3fv(n[2]);
  glVertex3fv(n[3]);
  glEnd();
}

/*****************************************************************/

void
initialize(void)
{
  GLfloat light0Pos[4] =
  {0.3, 0.3, 0.0, 1.0};
  GLfloat matAmb[4] =
  {0.01, 0.01, 0.01, 1.00};
  GLfloat matDiff[4] =
  {0.65, 0.65, 0.65, 1.00};
  GLfloat matSpec[4] =
  {0.30, 0.30, 0.30, 1.00};
  GLfloat matShine = 10.0;
  GLfloat eyePlaneS[] =
  {1.0, 0.0, 0.0, 0.0};
  GLfloat eyePlaneT[] =
  {0.0, 1.0, 0.0, 0.0};
  GLfloat eyePlaneR[] =
  {0.0, 0.0, 1.0, 0.0};
  GLfloat eyePlaneQ[] =
  {0.0, 0.0, 0.0, 1.0};

  /* Setup Misc.  */
  glClearColor(0.41, 0.41, 0.31, 0.0);

  glEnable(GL_DEPTH_TEST);

  glLineWidth(2.0);

  glCullFace(GL_FRONT);
  glEnable(GL_CULL_FACE);

  glMatrixMode(GL_PROJECTION);
  glFrustum(-0.5, 0.5, -0.5, 0.5, 1, 3);
  glMatrixMode(GL_MODELVIEW);
  glTranslatef(0, 0, -2);

  matrixIdentity((GLfloat *) objectXform);
  matrixIdentity((GLfloat *) textureXform);

  glMatrixMode(GL_PROJECTION);
  glPushMatrix();
  glLoadIdentity();
  glOrtho(0, 1, 0, 1, -1, 1);
  glMatrixMode(GL_MODELVIEW);
  glPushMatrix();
  glLoadIdentity();

  glRasterPos2i(0, 0);

  glPopMatrix();
  glMatrixMode(GL_PROJECTION);
  glPopMatrix();
  glMatrixMode(GL_MODELVIEW);

  /* Setup Lighting */
  glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, matAmb);
  glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, matDiff);
  glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, matSpec);
  glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, matShine);

  glEnable(GL_COLOR_MATERIAL);

  glLightfv(GL_LIGHT0, GL_POSITION, light0Pos);
  glEnable(GL_LIGHT0);

  glLightModeli(GL_LIGHT_MODEL_TWO_SIDE, GL_TRUE);
  glEnable(GL_LIGHTING);

  /* Setup Texture */
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
  (*loadTexture) ();

  glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
  glTexGenfv(GL_S, GL_EYE_PLANE, eyePlaneS);

  glTexGeni(GL_T, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
  glTexGenfv(GL_T, GL_EYE_PLANE, eyePlaneT);

  glTexGeni(GL_R, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
  glTexGenfv(GL_R, GL_EYE_PLANE, eyePlaneR);

  glTexGeni(GL_Q, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
  glTexGenfv(GL_Q, GL_EYE_PLANE, eyePlaneQ);
}

void
display(void)
{
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  if (textureEnabled) {
    if (mode == MoveTexture || mode == MoveView) {
      /* Have OpenGL compute the new transformation (simple but slow). */
      glPushMatrix();
      glLoadIdentity();
      glRotatef(angle, axis[0], axis[1], axis[2]);
      glMultMatrixf((GLfloat *) textureXform);
      glGetFloatv(GL_MODELVIEW_MATRIX, (GLfloat *) textureXform);
      glPopMatrix();
    }
    loadTextureProjection((GLfloat *) textureXform);

    if (showProjection) {
      glPushMatrix();
      glMultMatrixf((GLfloat *) textureXform);
      glDisable(GL_LIGHTING);
      drawTextureProjection();
      glEnable(GL_LIGHTING);
      glPopMatrix();
    }
    glEnable(GL_TEXTURE_2D);
    glEnable(GL_TEXTURE_GEN_S);
    glEnable(GL_TEXTURE_GEN_T);
    glEnable(GL_TEXTURE_GEN_R);
    glEnable(GL_TEXTURE_GEN_Q);
  }
  if (mode == MoveObject || mode == MoveView) {
    /* Have OpenGL compute the new transformation (simple but slow). */
    glPushMatrix();
    glLoadIdentity();
    glRotatef(angle, axis[0], axis[1], axis[2]);
    glMultMatrixf((GLfloat *) objectXform);
    glGetFloatv(GL_MODELVIEW_MATRIX, (GLfloat *) objectXform);
    glPopMatrix();
  }
  glPushMatrix();
  glMultMatrixf((GLfloat *) objectXform);
  (*drawObject) ();
  glPopMatrix();

  glDisable(GL_TEXTURE_2D);
  glDisable(GL_TEXTURE_GEN_S);
  glDisable(GL_TEXTURE_GEN_T);
  glDisable(GL_TEXTURE_GEN_R);
  glDisable(GL_TEXTURE_GEN_Q);

  if (zoomFactor > 1.0) {
    glDisable(GL_DEPTH_TEST);
    glCopyPixels(0, 0, winWidth / zoomFactor, winHeight / zoomFactor, GL_COLOR);
    glEnable(GL_DEPTH_TEST);
  }
  glFlush();
  glutSwapBuffers();
  checkErrors();
}

/*****************************************************************/

/* simple trackball-like motion control */
float lastPos[3];
int lastTime;

void
ptov(int x, int y, int width, int height, float v[3])
{
  float d, a;

  /* project x,y onto a hemi-sphere centered within width, height */
  v[0] = (2.0 * x - width) / width;
  v[1] = (height - 2.0 * y) / height;
  d = sqrt(v[0] * v[0] + v[1] * v[1]);
  v[2] = cos((M_PI / 2.0) * ((d < 1.0) ? d : 1.0));
  a = 1.0 / sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
  v[0] *= a;
  v[1] *= a;
  v[2] *= a;
}

void
startMotion(int x, int y, int but, int time)
{
  if (but == GLUT_LEFT_BUTTON) {
    mode = MoveView;
  } else if (but == GLUT_MIDDLE_BUTTON) {
    mode = MoveTexture;
  } else {
    return;
  }

  lastTime = time;
  ptov(x, y, winWidth, winHeight, lastPos);
}

void
animate(void)
{
  glutPostRedisplay();
}

void
vis(int visible)
{
  if (visible == GLUT_VISIBLE) {
    if (redrawContinuously)
      glutIdleFunc(animate);
  } else {
    if (redrawContinuously)
      glutIdleFunc(NULL);
  }
}

void
stopMotion(int but, int time)
{
  if ((but == GLUT_LEFT_BUTTON && mode == MoveView) ||
    (but == GLUT_MIDDLE_BUTTON && mode == MoveTexture)) {
  } else {
    return;
  }

  if (time == lastTime) {
    redrawContinuously = GL_TRUE;
    glutIdleFunc(animate);
  } else {
    angle = 0.0;
    redrawContinuously = GL_FALSE;
    glutIdleFunc(0);
  }
  if (!redrawContinuously) {
    mode = MoveNone;
  }
}

void
trackMotion(int x, int y)
{
  float curPos[3], dx, dy, dz;

  ptov(x, y, winWidth, winHeight, curPos);

  dx = curPos[0] - lastPos[0];
  dy = curPos[1] - lastPos[1];
  dz = curPos[2] - lastPos[2];
  angle = 90.0 * sqrt(dx * dx + dy * dy + dz * dz);

  axis[0] = lastPos[1] * curPos[2] - lastPos[2] * curPos[1];
  axis[1] = lastPos[2] * curPos[0] - lastPos[0] * curPos[2];
  axis[2] = lastPos[0] * curPos[1] - lastPos[1] * curPos[0];

  lastTime = glutGet(GLUT_ELAPSED_TIME);
  lastPos[0] = curPos[0];
  lastPos[1] = curPos[1];
  lastPos[2] = curPos[2];
  glutPostRedisplay();
}

/*****************************************************************/

void
object(void)
{
  static int object;

  object++;
  object %= 3;
  switch (object) {
  case 0:
    drawObject = drawCube;
    break;
  case 1:
    drawObject = drawDodecahedron;
    break;
  case 2:
    drawObject = drawSphere;
    break;
  default:
    break;
  }
}

static void
nop(void)
{
}

void
texture(void)
{
  static int texture = 0;

  texture++;
  texture %= 3;
  if (texture == 1 && texFilename == NULL) {
    /* Skip file texture if not loaded. */
    texture++;
  }
  switch (texture) {
  case 0:
    loadTexture = nop;
    textureEnabled = GL_FALSE;
    break;
  case 1:
    loadTexture = loadImageTexture;
    (*loadTexture) ();
    textureEnabled = GL_TRUE;
    break;
  case 2:
    loadTexture = loadSpotlightTexture;
    (*loadTexture) ();
    textureEnabled = GL_TRUE;
    break;
  default:
    break;
  }
}

void
help(void)
{
  printf("'h'   - help\n");
  printf("'l'   - toggle linear/nearest filter\n");
  printf("'s'   - toggle projection frustum\n");
  printf("'t'   - toggle projected texture\n");
  printf("'o'   - toggle object\n");
  printf("'z'   - increase zoom factor\n");
  printf("'Z'   - decrease zoom factor\n");
  printf("left mouse     - move view\n");
  printf("middle mouse   - move projection\n");
}

/* ARGSUSED1 */
void
key(unsigned char key, int x, int y)
{
  switch (key) {
  case '\033':
    exit(0);
    break;
  case 'l':
    linearFilter = !linearFilter;
    (*loadTexture) ();
    break;
  case 's':
    showProjection = !showProjection;
    break;
  case 't':
    texture();
    break;
  case 'o':
    object();
    break;
  case 'z':
    zoomFactor += 1.0;
    glPixelZoom(zoomFactor, zoomFactor);
    glViewport(0, 0, winWidth / zoomFactor, winHeight / zoomFactor);
    break;
  case 'Z':
    zoomFactor -= 1.0;
    if (zoomFactor < 1.0)
      zoomFactor = 1.0;
    glPixelZoom(zoomFactor, zoomFactor);
    glViewport(0, 0, winWidth / zoomFactor, winHeight / zoomFactor);
    break;
  case 'h':
    help();
    break;
  }
  glutPostRedisplay();
}

void
mouse(int button, int state, int x, int y)
{
  if (state == GLUT_DOWN)
    startMotion(x, y, button, glutGet(GLUT_ELAPSED_TIME));
  else if (state == GLUT_UP)
    stopMotion(button, glutGet(GLUT_ELAPSED_TIME));
  glutPostRedisplay();
}

void
reshape(int w, int h)
{
  winWidth = w;
  winHeight = h;
  glViewport(0, 0, w / zoomFactor, h / zoomFactor);
}

void
usage(char *name)
{
  fprintf(stderr, "usage: %s <image-filename>\n", name);
  fprintf(stderr, "\n");
}

void
menu(int selection)
{
  if (selection == 666) {
    exit(0);
  }
  key((unsigned char) selection, 0, 0);
}

int
main(int argc, char **argv)
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);
  (void) glutCreateWindow("projtex");
  if (argc > 2) {
    usage(argv[0]);
    exit(1);
  }
  if (argc > 1) {
    texFilename = argv[1];
  }
  loadTexture = loadImageTexture;
  drawObject = drawCube;
  initialize();
  glutDisplayFunc(display);
  glutKeyboardFunc(key);
  glutReshapeFunc(reshape);
  glutMouseFunc(mouse);
  glutMotionFunc(trackMotion);
  glutVisibilityFunc(vis);
  glutCreateMenu(menu);
  glutAddMenuEntry("Toggle showing projection", 's');
  glutAddMenuEntry("Switch texture", 't');
  glutAddMenuEntry("Switch object", 'o');
  glutAddMenuEntry("Toggle filtering", 'l');
  glutAddMenuEntry("Quit", 666);
  glutAttachMenu(GLUT_RIGHT_BUTTON);
  texture();
  glutMainLoop();
  return 0;             /* ANSI C requires main to return int. */
}
