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pythonopenglglutpyopenglopengl-compat

How to draw a line cube with OpenGL?

Im trying to draw a cube with lines.

And here's my code. It just gives me a white frame with nothing inside it. Nothing happens. What am I doing wrong here? Is it a problem with the order of calling out the functions or something wrong with the projection?


def myInit():
    glClearColor(0.0, 0.0, 0.0, 1.0) 
    glColor3f(0.2, 0.5, 0.4)
    gluPerspective(45, 1.33, 0.1, 50.0)


vertices= (
    (100, -100, -100),
    (100, 100, -100),
    (-100, 100, -100),
    (-100, -100, -100),
    (100, -100, 100),
    (100, 100, 100),
    (-100, -100, 100),
    (-100, 100, 100)
    )

edges = (
    (0,1),
    (0,3),
    (0,4),
    (2,1),
    (2,3),
    (2,7),
    (6,3),
    (6,4),
    (6,7),
    (5,1),
    (5,4),
    (5,7)
    )


def Display():
    glBegin(GL_LINES)
    for edge in edges:
        for vertex in edge:
            glVertex3fv(vertices[vertex])
    glEnd()

glutInit()
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB)   
glutInitWindowSize(800, 600)  
myInit()
glutDisplayFunc(Display) 
glutMainLoop()
Solution

  • All the geometry which is not in the Viewing frustum is clipped. The size of the cube i 200x200x200. You've to create a viewing frustum which is large enough.

    For instance set a perspective projection matrix gluPerspective with a far plane of 1000.0. The projection matrix is intended to be set to the current projection matrix (GL_PROJECTION). See glMatrixMode:

    glMatrixMode(GL_PROJECTION)
glLoadIdentity()
gluPerspective(45, 1.33, 0.1, 1000.0) 


Translate ([`glTranslate`](https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml/glTranslate.xml)) the model along the negative z axis, in between the near plane (0.1) and far (plane). The model or view matrix has to be set to the current model view matrix (`GL_MODELVIEW`):

```py
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
glTranslate(0, 0, -500)

    Clear the display in every frame by glClear:

    def Display():
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

    # [...]

    Swaps the buffers of the current double buffered window by glutSwapBuffers and continuously update the display by invoking glutPostRedisplay.

    def Display():
    # [...]

    glutSwapBuffers()
    glutPostRedisplay()

    See also Immediate mode and legacy OpenGL

    See the example:

    def init():
    glClearColor(0.0, 0.0, 0.0, 1.0) 
    
    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    gluPerspective(45, 1.33, 0.1, 1000.0)

    glMatrixMode(GL_MODELVIEW)
    glLoadIdentity()
    glTranslate(0, 0, -500)

def Display():
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

    glColor3f(0.2, 0.5, 0.4)
    glBegin(GL_LINES)
    for edge in edges:
        for vertex in edge:
            glVertex3fv(vertices[vertex])
    glEnd()

    glutSwapBuffers()
    glutPostRedisplay()