Question

In my scene I have a cube within a sphere. I would like to apply a RGB texture to a sphere and make it translucent. I can import the texture, apply it to the sphere and make it translucent but i am not getting the result I want.

My blend function is glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA)

My draw method is as follows:

def DrawGLScene():
    rotation1  = 60
    rotation2 = 60

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
    glEnable(GL_BLEND)
    glLoadIdentity()
    glTranslatef(0.0, 0.0, -8.0)
    glRotatef(rotation1, 1.0, 0.0, 0.0)
    glRotatef(rotation2, 0.0, 1.0, 0.0)
    glColor4f(1.0,1.0,1.0,1.0)

    glutSolidCube(2);
    glEnable(GL_COLOR_MATERIAL)
    glEnable(GL_TEXTURE_2D)
    glBindTexture(GL_TEXTURE_2D,1)
    glColor4f(1.0,1.0,1.0,0.3)
    Q=gluNewQuadric()
    gluQuadricNormals(Q, GL_SMOOTH)
    gluQuadricTexture(Q, GL_TRUE)
    glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, GL_SPHERE_MAP)
    glTexGeni(GL_T, GL_TEXTURE_GEN_MODE, GL_SPHERE_MAP)
    gluSphere(Q, 2.35, 32, 16)
    glDisable(GL_TEXTURE_2D)

    glutSwapBuffers()

The result looks like this:

It seemed there were depth problems as I could only see the back side of the sphere in parts in the bottom right. I then set glDepthFunc(GL_LESS) for drawing the cube and glDepthFunc(GL_ALWAYS) for drawing the sphere which resulted in:

Now the back side of the sphere is showing through the cube.

I have tried multiple combinations of glDepthFunc() for the objects but to no avail. Is the problem to do with how I am handling depth, blending or something else?

EDIT:

Using glEnable(GL_CULL_FACE) and glCullFace(GL_BACK) in the first example gives me the following which is still not correct as now you cannot see the back of the sphere at all.

Answer 1

First, glEnable(GL_CULL_FACE). Draw the sphere once with glCullFace(GL_FRONT). Draw the cube (without culling). Lastly, draw the sphere again with glCullFace(GL_BACK).