{  DEMO PROGRAM MADE BY MATTHIAS MOLSKI, August 2009
   VISIT: http://www.Freepascal-meets-SDL.net/  }

PROGRAM chap8;
USES CRT, SDL, GL, GLU;

VAR
userkey:CHAR;
screen:pSDL_SURFACE;
h,hh,th,thh:REAL;

BEGIN
//some calculations needed for a regular tetrahedron with side length of 1
h:=SQRT(0.75); //height of equilateral triangle
hh:=h/2;       //half height of equilateral triangle
th:=0.75;      //height of tetrahedron
thh:=th/2;     //half height of tetrahedron

SDL_INIT(SDL_INIT_VIDEO);

SDL_GL_SETATTRIBUTE(SDL_GL_RED_SIZE, 5);
SDL_GL_SETATTRIBUTE(SDL_GL_GREEN_SIZE, 5);
SDL_GL_SETATTRIBUTE(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SETATTRIBUTE(SDL_GL_DEPTH_SIZE, 16);
SDL_GL_SETATTRIBUTE(SDL_GL_DOUBLEBUFFER, 1);

screen:=SDL_SETVIDEOMODE(640, 480, 0, SDL_OPENGL);
IF screen=NIL THEN HALT;

glCLEARCOLOR(0.0, 0.0, 1.0, 0.0);
glVIEWPORT(0,0,640,480);
glMATRIXMODE(GL_PROJECTION);
glLOADIDENTITY;
gluPERSPECTIVE(45.0, 640.0/480.0, 1.0, 3.0);
glMATRIXMODE(GL_MODELVIEW);
glLOADIDENTITY;
glCLEAR(GL_COLOR_BUFFER_BIT);
glENABLE(GL_CULL_FACE);
glTRANSLATEf(0.0, 0.0, -2.0);

REPEAT
SDL_DELAY(50);

glROTATEf(5, 0.0, 1.0, 0.0);
glCLEAR(GL_COLOR_BUFFER_BIT);

glBEGIN(GL_TRIANGLES);
    glCOLOR3f(1.0, 1.0, 0.0);
    glVERTEX3f(thh, 0.0, 0.0);
    glVERTEX3f(-thh, hh, 0.0);
    glVERTEX3f(-thh, -hh, 0.5);

    glCOLOR3f(0.0, 1.0, 1.0);
    glVERTEX3f(thh, 0.0, 0.0);
    glVERTEX3f(-thh, -hh, -0.5);
    glVERTEX3f(-thh, hh, 0.0);

    glCOLOR3f(1.0, 0.0, 1.0);
    glVERTEX3f(thh, 0.0, 0.0);
    glVERTEX3f(-thh, -hh, 0.5);
    glVERTEX3f(-thh, -hh, -0.5);

    glCOLOR3f(1.0, 1.0, 1.0);
    glVERTEX3f(-thh, -hh, 0.5);
    glVERTEX3f(-thh, hh, 0.0);
    glVERTEX3f(-thh, -hh, -0.5);
glEND;

SDL_GL_SWAPBUFFERS;
UNTIL keypressed;

SDL_QUIT;
END.