/* Simplest demo of transparency

Written by Scott D. Anderson
scott.anderson@acm.org
Fall 2007
*/

#include <tw.h>

bool ShowScreen = false;

void display() {
    twDisplayInit();
    twCamera();
    glClearColor(0,0,0,0); //clear sub-window to black
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glPushAttrib(GL_ALL_ATTRIB_BITS);

    // Normal depth stuff
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL); 

    // Lighting
    GLfloat lightdir[4] = {1,1,1,0};
    twGrayLight(GL_LIGHT0,lightdir,0.1,0.8,0.5);
    glEnable(GL_LIGHTING);
    glShadeModel(GL_SMOOTH);

    // Draw solid stuff, a nice brass teapot, roughly brass.  I found "brass" at http://www.colourprep.com/hexColorsName.html
    twTriple brass = { 0xB5/255.0, 0xA6/255.0, 0x42/255.0 };
    twColor(brass,0.9,20);
    glutSolidTeapot(1);

    if(ShowScreen) {
        // switch to transparency
        glEnable(GL_BLEND);
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
        glDepthMask(GL_FALSE);
        
        // Turn off lighting
        glDisable(GL_LIGHTING);
    
        // Draw a sheer green screen in front of and to one side of the teapot
        glColor4f(0,1,0,0.5);

        GLfloat Z = 1.0;
        glBegin(GL_QUADS);
        glVertex3f(0,1,Z);
        glVertex3f(0,-1,Z);
        glVertex3f(1,-1,Z);
        glVertex3f(1,1,Z);
        glEnd();
    }
    glPopAttrib();

    glFlush();
    glutSwapBuffers(); 
}

void keys(unsigned char key, int x, int y) {
    switch(key) {
    case 's': ShowScreen = ! ShowScreen; break;
    }
    glutPostRedisplay();
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGBA | GLUT_ALPHA | GLUT_DEPTH | GLUT_DOUBLE);
    twInitWindowSize(500,500);
    glutCreateWindow(argv[0]);
    glutDisplayFunc(display);
    twBoundingBox(-1,1,-1,1,-1,1);
    twMainInit();
    twKeyCallback('s',keys,"toggle showing the screen");
    glutMainLoop();
    return 0;
}