FlexiVertexBuffer Sphere

Sphere FlexiVertexBuffer.mm

// Number of samples in each direction
static const int LongitudeSample=20,LatitudeSample=10;

- (void)addSphereAt:(float *)org sized:(float *)size
{
    // We'll generate the coordinates and normals ahead of time
    float coords[3*LongitudeSample*LatitudeSample];
    float norms[3*LongitudeSample*LatitudeSample];
    float texCoords[2*LongitudeSample*LatitudeSample];
    
    // Work our way around the equator, building vertices
    int ix=0;
    for (float lon=-180.0;ix<LongitudeSample;lon+=360.0/(LongitudeSample-1),ix++)
    {
        int iy=0;
        // Run from the south pole to the north
        for (float lat=-90.0;iy<LatitudeSample;lat+=180.0/(LatitudeSample-1),iy++)
        {
            // Generate a coordinate on the unit sphere
            float coord[3];
            float z = sinf(lat/180.0*M_PI);
            float rad = sqrtf(1.0-z*z);
            coord[0] = rad*cosf(lon/180.0*M_PI);
            coord[1] = rad*sinf(lon/180.0*M_PI);
            coord[2] = z;
            
            // The normal is the coordinate (on the unit sphere)
            float *thisNorm = &norms[3*(iy*LongitudeSample+ix)];
            thisNorm[0] = coord[0];  thisNorm[1] = coord[1];  thisNorm[2] = coord[2];

            // Scale the coordinate and save it off
            float *thisCoord = &coords[3*(iy*LongitudeSample+ix)];
            thisCoord[0] = coord[0]*size[0]+org[0];  thisCoord[1] = coord[1]*size[1]+org[1];  thisCoord[2] = coord[2]*size[2]+org[2];
            
            // And texture coordinates
            float *texCoord = &texCoords[2*(iy*LongitudeSample+ix)];
            texCoord[0] = ix/(float)(LongitudeSample-1);
            texCoord[1] = iy/(float)(LatitudeSample-1);
        }
    }
    
    // Now for the triangles, we need two per sample
    for (int ix=0;ix<LongitudeSample-1;ix++)
        for (int iy=0;iy<LatitudeSample-1;iy++)
        {
            // Lower left triangle
            [_vertices appendBytes:&coords[3*(iy*LongitudeSample+ix)] length:sizeof(float)*3];
            [_vertices appendBytes:&norms[3*(iy*LongitudeSample+ix)] length:sizeof(float)*3];
            [_vertices appendBytes:&texCoords[2*(iy*LongitudeSample+ix)] length:sizeof(float)*2];
            [_vertices appendBytes:&coords[3*(iy*LongitudeSample+ix+1)] length:sizeof(float)*3];
            [_vertices appendBytes:&norms[3*(iy*LongitudeSample+ix+1)] length:sizeof(float)*3];
            [_vertices appendBytes:&texCoords[2*(iy*LongitudeSample+ix+1)] length:sizeof(float)*2];
            [_vertices appendBytes:&coords[3*((iy+1)*LongitudeSample+ix)] length:sizeof(float)*3];
            [_vertices appendBytes:&norms[3*((iy+1)*LongitudeSample+ix)] length:sizeof(float)*3];
            [_vertices appendBytes:&texCoords[2*((iy+1)*LongitudeSample+ix)] length:sizeof(float)*2];

            // Upper right triangle
            [_vertices appendBytes:&coords[3*(iy*LongitudeSample+ix+1)] length:sizeof(float)*3];
            [_vertices appendBytes:&norms[3*(iy*LongitudeSample+ix+1)] length:sizeof(float)*3];
            [_vertices appendBytes:&texCoords[2*(iy*LongitudeSample+ix+1)] length:sizeof(float)*2];
            [_vertices appendBytes:&coords[3*((iy+1)*LongitudeSample+ix+1)] length:sizeof(float)*3];
            [_vertices appendBytes:&norms[3*((iy+1)*LongitudeSample+ix+1)] length:sizeof(float)*3];
            [_vertices appendBytes:&texCoords[2*((iy+1)*LongitudeSample+ix+1)] length:sizeof(float)*2];
            [_vertices appendBytes:&coords[3*((iy+1)*LongitudeSample+ix)] length:sizeof(float)*3];
            [_vertices appendBytes:&norms[3*((iy+1)*LongitudeSample+ix)] length:sizeof(float)*3];
            [_vertices appendBytes:&texCoords[2*((iy+1)*LongitudeSample+ix)] length:sizeof(float)*2];
        }

    // Coordintes + Normals + Texture coordinates
    _vertexSize = 3*sizeof(float)+ 3*sizeof(float)+ 2*sizeof(float);
    _hasTextureCoords = true;
    _numVertices += (LongitudeSample-1)*(LatitudeSample-1)*2*3;
}