3D pyramid appears scattered, with mixed up sides - c

Question

First of all I defined a structure to express the coordinated of a pyramid:
typedef struct
{
GLfloat xUp;
GLfloat yUp;
GLfloat zUp;
GLfloat base;
GLfloat height;
}pyramid;
Pretty self-explanatory here : I store the coordinates of the uppest point, the base and the height.
The I wrote a function to draw a pyramid:
void drawPyramid(pyramid pyr)
{
GLfloat p1[]= {pyr.xUp+pyr.base/2.0, pyr.yUp-pyr.height, pyr.zUp-pyr.base/2.0};
GLfloat p2[]= {pyr.xUp+pyr.base/2.0, pyr.yUp-pyr.height, pyr.zUp+pyr.base/2.0};
GLfloat p3[]= {pyr.xUp-pyr.base/2.0, pyr.yUp-pyr.height, pyr.zUp+pyr.base/2.0};
GLfloat p4[]= {pyr.xUp-pyr.base/2.0, pyr.yUp-pyr.height, pyr.zUp-pyr.base/2.0};
GLfloat up[]= {pyr.xUp, pyr.yUp, pyr.zUp};
glBegin(GL_TRIANGLES);
glColor4f(1.0, 0.0, 0.0, 0.0);
glVertex3fv(up);
glVertex3fv(p1);
glVertex3fv(p2);
glColor4f(0.0, 1.0, 0.0, 0.0);
glVertex3fv(up);
glVertex3fv(p2);
glVertex3fv(p3);
glColor4f(0.0, 0.0, 1.0, 0.0);
glVertex3fv(up);
glVertex3fv(p3);
glVertex3fv(p4);
glColor4f(1.0, 1.0, 0.0, 0.0);
glVertex3fv(up);
glVertex3fv(p4);
glVertex3fv(p1);
glEnd();
glColor4f(0.0, 1.0, 1.0, 0.0);
glBegin(GL_QUADS);
glVertex3fv(p1);
glVertex3fv(p2);
glVertex3fv(p3);
glVertex3fv(p4);
glEnd();
}
I struggled to draw all the vertices in anti-clockwise order, but probably I messed up something.
This is how I display the pyramid in my rendering function:
void display()
{
glClearColor(0.0, 0.0, 0.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glTranslatef(0.0, -25.0, 50.0);
glRotatef(-angle, 0.0, 1.0, 0.0);
glTranslatef(0.0, 25.0, -50.0);
pyramid pyr;
pyr.xUp=0.0;
pyr.yUp=10.0;
pyr.zUp=50.0;
pyr.base=10.0;
pyr.height=18.0;
glColor4f(1.0, 0.0, 0.0, 0.0);
drawPyramid(pyr);
glutSwapBuffers();
}
I also use an init method called before the glut main loop:
void init()
{
glEnable(GL_DEPTH);
glViewport(-1.0, 1.0, -1.0, 1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(35.0, 1.0, 1.0, 100.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0.0,1.0,0.0, 0.0,1.0,30.0, 0.0,1.0,0.0);
}
angle is just a double that I use to rotate the pyramid, changeable by pressing 'r', but this is not relevant.It appears that the real problem is how I draw the vertices.
The problem is that the faces of the pyramid appear scattered, messed up.I would better describe this situation with an image:
There's a face that is too small, that is displayed and I don't know why.
If I rotate the pyramid it appears messed up, I even recored a video to describe this.
Later I could upload it if the problem is not totally clear.
PS: Many people have noticed that I am using outdated techniques.But unfortunately this is what my university offers.
EDIT
I forgot to say about the main function:
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitWindowPosition(100, 100);
glutInitWindowSize(500, 500);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutCreateWindow("Sierpinsky Pyramid");
glutDisplayFunc(display);
glutKeyboardFunc(keyboard);
init();
glutMainLoop();
return 0;
}

Answer 1

It looks like depth buffer isn't initialzied.
Calling glEnable(GL_DEPTH_TEST) is not enough. You must correctly initialize glut and specify that you want depth buffer support, otherwise you won't get a depth buffer. If I remember correctly, this is done using glutInitDisplayMode(GLUT_DEPTH|...). See documentation here and introduction here. Additional info can be found using google.
--EDIT--
You're passing invalid parameter to glEnable. call glEnable(GL_DEPTH_TEST) instead of glEnable(GL_DEPTH).
Also:
Matrix code in display function isn't protected by glPushMatrix/glPopMatrix. Which means that every time you rotate pyramid, rotation is applied to previous transform. I.e. calling display function will rotate the pyramid.
glViewport is called with invalid parameters. glViewport takes 4 integer arguments, but you're trying to pass floats. Also, what's "width of -1.0" supposed to mean?
You have not checked any error codes (glGetError). If you tried to call glGetError after glEnable call, then you'd see that it returns GL_INVALID_ENUM.
OpenGL has documentation. Documentation is available on opengl.org. Use it and read it. Also, I'd recommend reading "OpenGL red book".