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Drawing a globe with OpenGL ES

I am trying to make a globe (a sphere with maps on it) with OpenGL ES 1.1 on iOS.

I can draw a sphere and draw borders, but with one problem: lines that are not facing my view are also drawn on the screen . Like this:

Globe with lines on the back being shown

The picture shows that America looks great, but you can see Australia on its back. It should not be displayed because it is at the back of the globe, and the BLACK and PURPLE bands in the globe are not transparent.

Any ideas on what options should be tuned in order to get the right globe?

If this helps, I can post the relevant parts of the code . Just ask in which part, and I will update the question.

Thank you very much in advance.

: , Sphere:

glEnableClientState(GL_VERTEX_ARRAY);
glPolygonOffset(-1.0f, -1.0f);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
int x, y;
GLfloat curR, curG, curB;
curR = curG = curB = 0.15f;
for (y=0; y<EARTH_LAT_RES; y++) {
    if (y%10 == 0) {
        glColor4f(curR, curG, curB, 1.0f);
        curR = curR == 0.15f ? 0.6f : 0.15f;
        curB = curB == 0.15f ? 0.6f : 0.15f;
    }
    for (x=0; x<EARTH_LON_RES; x++) {
        Vertex3D vs[4];
        vs[1] = vertices[x][y];
        vs[0] = vertices[x][y+1];
        vs[3] = vertices[x+1][y];
        vs[2] = vertices[x+1][y+1];
        glVertexPointer(3, GL_FLOAT, 0, vs);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    }
}
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glDisable(GL_POLYGON_OFFSET_FILL);
glDisableClientState(GL_VERTEX_ARRAY);

, :

// vxp is a data structure with vertex arrays that represent
// border lines
int i;
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnableClientState(GL_VERTEX_ARRAY);
for (i=0; i<vxp->nFeatures; i++)
{
    glVertexPointer(3, GL_FLOAT, 0, vxp->pFeatures[i].pVerts);
    glDrawArrays(GL_LINE_STRIP, 0, vxp->pFeatures[i].nVerts);
}
glDisableClientState(GL_VERTEX_ARRAY);
glDisable(GL_BLEND);

, :

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glEnable(GL_DEPTH_TEST); /* enable depth testing; required for z-buffer */
glEnable(GL_CULL_FACE); /* enable polygon face culling */ 
glCullFace(GL_BACK);
glOrthof(-1.0f, 1.0f, -1.5f, 1.5f, -1.0f, 1.0f);
glFrustumf (-1.0, 1.0, -1.5, 1.5, -1.0, 1.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
+3
1

, , , , , . glPolygonOffset, " " , , . - :

// add a small bit of offset, so that lines that should be visible aren't
// clipped due to depth rounding errors; note that ES allows GL_POLYGON_OFFSET_FILL
// but not GL_POLYGON_OFFSET_LINE, so we're going to push the polygons back a bit
// in terms of values written to the depth buffer, rather than the more normal
// approach of pulling the lines forward a bit
glPolygonOffset(-1.0, -1.0);
glEnable(GL_POLYGON_OFFSET_FILL);

// disable writes to the colour buffer
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);

drawSolidPolygonalSphere();

// enable writing again
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);

// disable the offset
glDisable(GL_POLYGON_OFFSET_FILL);

drawVectorMap();

, , . , , , . glGet, , , ( ), , .

+5

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