/*
 *  alphablendnosort.c
 *  Celeste Fowler, 1997
 *  
 *  Shows the artifacts that can be seen when using alpha blending for
 *  transparency and no sorting is performed.
 *
 */

#include <assert.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <GL/glut.h>
#ifdef _WIN32
#include <sys/timeb.h>
#else
#include <sys/time.h>
#endif

GLUquadricObj *cone, *base, *qsphere;

#ifdef _WIN32
int
gettimeofday(struct timeval* tp)
{
    struct timeb tb;

    ftime(&tb);
    tp->tv_sec = tb.time;
    tp->tv_usec = tb.millitm * 1000;

    /* 0 indicates that the call succeeded. */
    return 0;
}
#endif

void init(void)
{
    static GLfloat lightpos[] = {.5, .75, 1.5, 1};

    glEnable(GL_DEPTH_TEST); 
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);

    glLightfv(GL_LIGHT0, GL_POSITION, lightpos);

    cone = gluNewQuadric();
    base = gluNewQuadric();
    qsphere = gluNewQuadric();
    gluQuadricOrientation(base, GLU_INSIDE);

    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
}

void reshape(GLsizei w, GLsizei h) 
{
    glViewport(0, 0, w, h);
  
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60, 1, .01, 10);
    gluLookAt(0, 0, 2.577, 0, 0, -5, 0, 1, 0);
  
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void draw_room(void)
{
    /* material for the walls, floor, ceiling */
    static GLfloat wall_mat[] = {1.f, 1.f, 1.f, 1.f};

    glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, wall_mat);

    glBegin(GL_QUADS);
  
  /* floor */
    glNormal3f(0, 1, 0);
    glVertex3f(-1, -1, 1);
    glVertex3f(1, -1, 1);
    glVertex3f(1, -1, -1);
    glVertex3f(-1, -1, -1);

    /* ceiling */
    glNormal3f(0, -1, 0);
    glVertex3f(-1, 1, -1);
    glVertex3f(1, 1, -1);
    glVertex3f(1, 1, 1);
    glVertex3f(-1, 1, 1);  

    /* left wall */
    glNormal3f(1, 0, 0);
    glVertex3f(-1, -1, -1);
    glVertex3f(-1, -1, 1);
    glVertex3f(-1, 1, 1);
    glVertex3f(-1, 1, -1);

    /* right wall */
    glNormal3f(-1, 0, 0);
    glVertex3f(1, 1, -1);
    glVertex3f(1, 1, 1);
    glVertex3f(1, -1, 1);
    glVertex3f(1, -1, -1);

    /* far wall */
    glNormal3f(0, 0, 1);
    glVertex3f(-1, -1, -1);
    glVertex3f(1, -1, -1);
    glVertex3f(1, 1, -1);
    glVertex3f(-1, 1, -1);

    glEnd();
}

void draw_cone(void)
{
    static GLfloat cone_mat[] = {0.f, .5f, 1.f, 1.f};

    glPushMatrix();
    glTranslatef(0, -1, 0);
    glRotatef(-90, 1, 0, 0);

    glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, cone_mat);
    gluCylinder(cone, .3, 0, 1.25, 20, 1);
    gluDisk(base, 0., .3, 20, 1); 

    glPopMatrix();
}

void draw_sphere(GLdouble angle)
{
    static GLfloat sphere_mat[] = {1.f, .5f, 0.f, .5f};

    glPushMatrix();
    glTranslatef(0, -.3, 0);
    glRotatef(angle, 0, 1, 0);
    glTranslatef(0, 0, .6);

    glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, sphere_mat);
    gluSphere(qsphere, .3, 20, 20);

    glPopMatrix();
}

GLdouble get_secs(void)
{
    struct timeval t;
    gettimeofday(&t);
    return (t.tv_sec % 60) + t.tv_usec / 1000000.;
}

void draw(void)
{
    GLenum err;
    GLdouble secs;

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    draw_room();
    draw_cone();

    glEnable(GL_BLEND);
    secs = get_secs();
    draw_sphere(secs * 360. / 10.);
    glDisable(GL_BLEND);

    err = glGetError();
    if (err != GL_NO_ERROR) printf("Error:  %s\n", gluErrorString(err));

    glutSwapBuffers();
}

static int idle = 1;

void key(unsigned char key, int x, int y)
{
    if (key == 27) exit(0);
    idle = (idle == 0);
    if (idle) {
	glutIdleFunc(draw);
    } else {
	glutIdleFunc(0);
    }
}

void visible(int state)
{
    if (state == GLUT_VISIBLE && idle)
	glutIdleFunc(draw);
    else
	glutIdleFunc(NULL);
}

int main(int argc, char *argv[])
{
    glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);
    glutInitWindowPosition(0, 0);
    glutInitWindowSize(512, 512);
    glutInit(&argc, argv);

    glutCreateWindow(argv[0]);
    glutDisplayFunc(draw);
    glutIdleFunc(draw);
    glutKeyboardFunc(key);
    glutReshapeFunc(reshape);
    glutVisibilityFunc(visible);

    init();
    glutMainLoop();
    return 0;
}