/* Demo of three interpenetrating quads, to show transparency.

Implemented Fall 2003
Scott D. Anderson
*/

#include <stdio.h>
#include <GL/glut.h>
#include <tw.h>

bool BgBlack = true;
bool MidTrans = false;
bool DepthTest = true;

// I'm trying to make the cross section have an equilateral triangle, in
// the unit square, so this constant is useful, since it's the slope of
// the non-horizontal lines.
const float C=1.7320508075688772; // sqrt(3);

void display(void) {
    if(BgBlack) 
        glClearColor(0,0,0,0);        // transparent black
    else
        glClearColor(1,1,1,1);        // opaque white
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    twCamera();

    // Transparent Objects
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glEnable(GL_BLEND);

    if(!DepthTest)
        glDepthMask(GL_FALSE);

    glBegin(GL_QUADS);

    if(MidTrans)
        glColor4f(0,1,0,0.5);        // middle opaque green
    else
        glColor4f(0,1,0,0.7);        // fairly opaque green
    glVertex3f(0,1,0);                // back left
    glVertex3f(0,1,1);                // front left
    glVertex3f(1/C,0,1);        // front right
    glVertex3f(1/C,0,0);        // back right

    if(MidTrans)
        glColor4f(0,0,1,0.5);        // middle opaque blue
    else
        glColor4f(0,0,1,0.3);        // fairly transparent blue
    glVertex3f(1-1/C,0,0);        // back left
    glVertex3f(1-1/C,0,1);        // front left
    glVertex3f(1,1,1);                // front right
    glVertex3f(1,1,0);                // back right

    glEnd();

    glEnable(GL_DEPTH_TEST);
    glDepthMask(GL_TRUE);        // this is the default
    glDisable(GL_BLEND);

    // Opaque Objects
    glBegin(GL_QUADS);

    glColor4f(1,0,0,1);                // solid red
    glVertex3f(0,C/2,0);        // back left
    glVertex3f(0,C/2,1);        // front left
    glVertex3f(1,C/2,1);        // front right
    glVertex3f(1,C/2,0);        // back right

    glEnd();
    
    glFlush();
    glutSwapBuffers();
}

void keys(unsigned char k, int, int) {
    switch(k) {
    case 'b': BgBlack = !BgBlack; break;
    case 'd': DepthTest = !DepthTest; break;
    case 'm': MidTrans = !MidTrans; break;
    }
    glutPostRedisplay();
}

int main(int argc, char** argv) {
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
  twInitWindowSize(500,500);
  glutCreateWindow(argv[0]);
  glutDisplayFunc(display);
  twBoundingBox(0,1,0,1,0,1);
  twMainInit();            
  twKeyCallback('b',keys,"toggle black background");
  twKeyCallback('d',keys,"toggle depth test");
  twKeyCallback('m',keys,"toggle middle transparency");
  glutMainLoop();
  return 0;
}