Mesh face winding

[serengeor]

Today and yesterday I was having trouble understanding why my faces are culled with backface culling enabled in opengl.
I can't figure out how the winding works ( I thought I knew before )

Does it matter how vertices are arranged in array?
Or does only indices matter when winding a mesh? If so that would mean that no matter how vertices are arranged in array as long as indices point to same vertices the winding wouldn't differ?

[CuteAlien]

Vertex order shouldn't matter as only the indices describe the order. That's unless you work without indices in which case I think some defaults are used and then vertex order would matter.

[Mel]

The indices matters. They describe the order of the sides of a triangle and thus its winding. The only way to make sure that nothing is hidden wrong is to disable the backface culling.

[serengeor]

Vertex order shouldn't matter as only the indices describe the order. That's unless you work without indices in which case I think some defaults are used and then vertex order would matter.

The indices matters. They describe the order of the sides of a triangle and thus its winding.

I see, so I knew it correctly from the beginning
Then it must be something wrong with indices.

The only way to make sure that nothing is hidden wrong is to disable the backface culling.

the thing is that front faces get culled and back faces don't with backface culling.



If I wind them CW I get normal results, but I my front faces are set to CCW.

Here's how I wind the cube:


Faces:

Code: Select all

 
faceIndices
({
    {7,6,5,4},///top
    {4,5,1,0},///front
    {5,6,2,1},///right
    {6,7,3,2},///back
    {7,4,0,3},///left
    {0,1,2,3} ///bottom
})
 

winding order:

Code: Select all

 
faceWindingMain({0,3,1,1,3,2})
 

winding code:

Code: Select all

 
for(boost::uint32_t i = 0; i < 6; i++)
    {
        const boost::uint8_t voffset = (i*4) + size;
        const boost::uint8_t ioffset = (i*6) + isize;
 
        const boost::uint8_t * winding = /*invertFaceWinding(this->p_nodeVerts, (ECubeFace)i) ? faceWindingInverse :*/ faceWindingMain ;
 
        vertices[0 + voffset] = (Vertex3d(this->p_nodeVerts[faceIndices[i][0]], p_quadTexCoords[0]));
 
        vertices[1 + voffset] = (Vertex3d(this->p_nodeVerts[faceIndices[i][1]], p_quadTexCoords[1]));
 
        vertices[2 + voffset] = (Vertex3d(this->p_nodeVerts[faceIndices[i][2]], p_quadTexCoords[2]));
 
        vertices[3 + voffset] = (Vertex3d(this->p_nodeVerts[faceIndices[i][3]], p_quadTexCoords[3]));
 
        indices[0 + ioffset] = (winding[0]+voffset);
        indices[1 + ioffset] = (winding[1]+voffset);
        indices[2 + ioffset] = (winding[2]+voffset);
 
        indices[3 + ioffset] = (winding[3]+voffset);
        indices[4 + ioffset] = (winding[4]+voffset);
        indices[5 + ioffset] = (winding[5]+voffset);
 }
 

I've been trying to fix this for two days, so I thought that it wouldn't hurt if some spare eyes would help
I hope I've given enough information.

[hybrid]

You chose a hard one to imagine in the current place and orientation of the cube. But talking about the side facing us, the correct index order is 0,4,1,1,4,5. Irrlicht uses clock-wise winding, so drawing the triangles should go in that order when viweing the front-sides.

[serengeor]

But talking about the side facing us, the correct index order is 0,4,1,1,4,5. Irrlicht uses clock-wise winding, so drawing the triangles should go in that order when viweing the front-sides.

That would be clock wise winding? I'm using CCW since that's default on opengl, I think.

P.S. I'm rendering this with my own opengl renderer.

[hybrid]

Ah, ok. OpenGL uses CCW, so counter-clock wise by default.

[serengeor]

Fixed it all.
Thanks for the help