/* Demonstrates lighting of Bezier surfaces, comparing a glut cylinder
   with a Bezier piece like the Coke bottle.
   
Written by Scott D. Anderson
scott.anderson@acm.org
Fall 2004
*/

#include <stdio.h>
#include <math.h>
#include <tw.h>

GLfloat CurveCP[4][3] = { {1, 2.0, 0},
                          {1, 1.9, 0},
                          {1, 0.1, 0},
                          {1, 0.0, 0}};

GLfloat SurfaceCP[4][4][3];

void circular_slice(GLfloat surface_cp[4][4][3], GLfloat silhouette_cp[4][3]) {
    GLfloat radius, dist;
    int i,j;
    // i moves from one silhouette CP to another
    for(i=0; i<4; i++) {
        // j copies all the y values for these CPs, since they all have the same y
        for(j=0;j<4; j++) {
            surface_cp[i][j][1] = silhouette_cp[i][1];
        }
        radius = silhouette_cp[i][0];
        dist = radius*0.552; // distance of inner control points
        // circle CP0 is right on the silhouette, so x values are the same
        surface_cp[i][0][0] = radius;
        surface_cp[i][0][2] = 0.0;
        // CP1 is in front of the silhouette, at the same x, just 0.552 on the Z
        surface_cp[i][1][0] = radius;
        surface_cp[i][1][2] = dist;
        // CP2 is in front the silhouette, at the same Z as the CP3
        surface_cp[i][2][0] = dist;
        surface_cp[i][2][2] = radius;
        // CP3 is at x=0, with Z being the X value of the silhouette CP
        surface_cp[i][3][0] = 0.0;
        surface_cp[i][3][2] = radius;
    }
#if DEBUG    
    for(i=0;i<4;i++)
        for(j=0;j<4;j++)
            printf("{%4.2f,%4.2f,%4.2f}\n",
                   SurfaceCP[i][j][0],
                   SurfaceCP[i][j][1],
                   SurfaceCP[i][j][2]);
#endif
}

void surfaceInit() {
    circular_slice(SurfaceCP,CurveCP);
}

void draw_bezier_surface(GLfloat* cp) {
    int hsteps = 8;                // horizontal; 8 steps per quarter
    int vsteps = 1;                // vertical
    glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 4, 0, 1, 12, 4, cp);
    glEnable(GL_MAP2_VERTEX_3);
    glEnable(GL_AUTO_NORMAL);

    glMapGrid2f(hsteps,0.0,1.0,vsteps,0.0,1.0);
    glEvalMesh2(GL_FILL,0,hsteps,0,vsteps);
    twError();
}

void draw_circular_slice(GLfloat cp[4][4][3]) {
    int q=0;
    // q is the quadrant of the circular cross-section that we're drawing.
    glPushMatrix();
    for(;;) {
        draw_bezier_surface(&cp[0][0][0]);
        if(q++>=4) break;
        glRotatef(90,0,1,0);
    }
    glPopMatrix();
}

void display(void) {
    twDisplayInit();
    twCamera();

    GLfloat light0Pos[] = {0, 0, 1, 0};
    twGrayLight(GL_LIGHT0,light0Pos,1,1,1);
    glEnable(GL_LIGHT0);

    glEnable(GL_LIGHTING);
    glShadeModel(GL_SMOOTH);
    twAmbient(0.2);

    twTriple objColor = {0.2, 0.3, 0.4};
    twColor(objColor,0.9,20);        

    glPushMatrix();
    glTranslatef(-1,0,0);
    glRotatef(-90,1,0,0);        // z points up
    twCylinder(1,1,2,32,1);        // left cylinder has 32 circumference steps
    glPopMatrix();

    glPushMatrix();
    glTranslatef(1,0,0);
    twError();
    draw_circular_slice(SurfaceCP);
    twError();
    glPopMatrix();

    glFlush();
    glutSwapBuffers();
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    twInitWindowSize(500,500);
    glutCreateWindow(argv[0]);
    surfaceInit();
    glutDisplayFunc(display);
    twBoundingBox(-2,2,0,2,-1,1);
    twMainInit();
    glutMainLoop();
    return 0;
}