/*
 * 1D textured rainbow demo from Chapter 8.
 *
 * Written by Michael Sweet
 */

/* Added the ability to turn the rainbow on/off using the 'R' keyboard callback
   Scott D. Anderson
   Fall 2000 original
   Fall 2003 adapted to use TW.
*/

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

bool Rainbow = true;                // whether to show the rainbow.

void key(unsigned char k, int x, int y) {
    Rainbow = !Rainbow;
    glutPostRedisplay();
}

void rainbowInit() {
    static GLubyte roygbiv[8][3] =
        {
            { 0x3f, 0x00, 0x3f }, /* Dark Violet (for 8 colors...) */
            { 0x7f, 0x00, 0x7f }, /* Violet */
            { 0xbf, 0x00, 0xbf }, /* Indigo */
            { 0x00, 0x00, 0xff }, /* Blue */
            { 0x00, 0xff, 0x00 }, /* Green */
            { 0xff, 0xff, 0x00 }, /* Yellow */
            { 0xff, 0x7f, 0x00 }, /* Orange */
            { 0xff, 0x00, 0x00 }  /* Red */
        };
    /* Load the texture data */
    glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexImage1D(GL_TEXTURE_1D, 0, 3, 8, 0, GL_RGB, GL_UNSIGNED_BYTE, roygbiv);
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
}

void display(void) {
    twDisplayInit(0.5,0.5,1.0);        // clear to sky blue
    twError();
    twCamera();

    /* this is the green ground, drawn as an enormous circle, which is
       what gives the horizon its slightly curved appearance. */
    glDisable(GL_TEXTURE_1D);        // have to make sure textures are off
    glColor3f(0.0, 0.8, 0.0);
    glPushMatrix();
    glRotatef(-90,1,0,0);        // now z points up
    twDisk(100,30);
    glPopMatrix();

    twError();
    rainbowInit();
    /* Then a rainbow... */
    twColorName(TW_YELLOW);     // draw in Yellow, but this is irrelevant
                                // if decal texture-mapping is enabled
    if(Rainbow) {
        glEnable(GL_TEXTURE_1D);
    }
    twError();
    glBegin(GL_QUAD_STRIP);
    for (float th = 0.0; th <= M_PI; th += (0.03125 * M_PI)) {
        float x = cos(th) * 50.0;
        float y = sin(th) * 50.0;
        float z = -50.0;
        if(Rainbow) glTexCoord1f(0.0);
        glVertex3f(x, y, z);

        x = cos(th) * 55.0;
        y = sin(th) * 55.0;
        z = -50.0;
        if(Rainbow) glTexCoord1f(1.0);
        glVertex3f(x, y, z);
    }
    glEnd();
    twError();
    
    glFinish();
    glutSwapBuffers();
}

main(int  argc, char *argv[]) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
    twInitWindowSize(600,500);
    glutCreateWindow(argv[0]);
    twBoundingBox(-100,100,0,50,-100,100);
    twMainInit();
    twKeyCallback('R',key,"Toggle whether to show the rainbow");
    glutDisplayFunc(display);
    glutMainLoop();
    return (0);
}