Generating UV Data



  • On 25/05/2013 at 21:30, xxxxxxxx wrote:

    User Information:
    Cinema 4D Version:   14 
    Platform:   Windows  ;   
    Language(s) :     C++  ;

    ---------
    Hi everybody.

    I am currently writing on a small application which exports some 3D Game Models to Cinema 4D. For writing the file I am using the current SDK (Melange 6). In my original structure I have a list of edges. A edge consists of a verticle (3D Point Structure in absolute coordinates) and UV Information (2D Point Structure in floating point values from 0-1). 3 edges represent a triangle polygon.

    Generating the 3D Model was quite a simple task: Create the polygon object, resize it, write the verticles and polygons to GetPointW() / GetPolygonW() arrays.

    But now I want to generate the UVW Tags to generate the textures later on. I also thought it would be quite easy but for some unknown reason, the mesh isn't placed well.

    Here is a simplified code of my implementation:

    Vector* verticles = c4dPolygon->GetPointW();
    CPolygon* polygons = c4dPolygon->GetPolygonW();
    UVWTag* uvw = (UVWTag* )baseObject->addTag(Tuvw);
    UVWHandle uvwptr = uvw->GetDataAddressW();
    for(int i = 0; i < polygonCount * 3; i++)
    {
       Edge* e = edges[i];
       verticles[v++] = Vector(e->Position.X, e->Position.Y, e->Position.Z);
       if( (i+1) % 3 == 0 && i >= 2)
       {
          Edge* e1 = edges[v-3];
          Edge* e2 = edges[v-2];
          Edge* e3 = edges[v-1];
          polygons[p++] = CPolygon(v-1, v-2, v-3);
          uvw->Set(uvwptr, p-1, 
                    UVWStruct(
                      Vector(e1->UV.X, e1->UV.Y,0)
                      Vector(e2->UV.X, e2->UV.Y,0)
                      Vector(e3->UV.X, e3->UV.Y,0)
                    );      
       }
    }
    

    If I inspect the UV in Cinema 4D I can only see dots instead of the full polygons. The dots seem to be positioned well along the texture, but the polygons are simply not unfolded and the texture is misplaced because of that. Can somebody of you explain me why the UV is not unfolded well? Maybe it's a setting when creating the UVW.

    Here a screenshot of the result:

    Greetings



  • On 26/05/2013 at 01:18, xxxxxxxx wrote:

    Hi,

    nice Asari you have there.

    I had a similar problem with generating UVW data before. The result in the viewport looked similar.
    Maybe this thread can help you: https://plugincafe.maxon.net/topic/6551/7080_programmatically-creating-uvws&KW=uvw&PID=29557#29557

    Best,
    -Niklas



  • On 26/05/2013 at 10:28, xxxxxxxx wrote:

    After a quick glance, a few questions come to mind...

      
    Vector* verticles = c4dPolygon->GetPointW();
    CPolygon* polygons = c4dPolygon->GetPolygonW();
    UVWTag* uvw = (UVWTag* )baseObject->addTag(Tuvw);
    

    ...is there some reason you are using c4dPolygon (the PolygonObject) to get the vector/polygon pointers, but you are using baseObject (which I _assume_ IS in fact the BaseObject of that c4dPolygon object) to add the UVW tag to?

    (I haven't used Melange, so I'm not sure if there's some reason that you're not using MakeTag on the c4dPolygon object)

    Also, you should never use pointers without checking for NULL first.

      
       if( (i+1) % 3 == 0 && i >= 2)
       {
          Edge* e1 = edges[v-3];
          Edge* e2 = edges[v-2];
          Edge* e3 = edges[v-1];
          polygons[p++] = CPolygon(v-1, v-2, v-3);
          uvw->Set(uvwptr, p-1, 
                    UVWStruct(
                      Vector(e1->UV.X, e1->UV.Y,0)
                      Vector(e2->UV.X, e2->UV.Y,0)
                      Vector(e3->UV.X, e3->UV.Y,0)
                    );      
       }
    

    Note that inside this loop, you are using 2 different (reversed of each other) "winding orders" of the polygon indices vs uv-polygon indices.  In other words, you are setting up the polygon as:

    0
     /\
    1-2

    ...but the UV coordinates are being assigned as:

    2
     /\
    1-0

    ...this could cause the 'wrong' UV values to be assigned to the polygon vertices (with only a 'single' vertex having the correct UV value, in each triangular polygon).

    From your image, it _looks like_ your polygons are the thing that might be inverted (normals facing the wrong way), so to fix it try this....

      
          polygons[p++] = CPolygon(v-3, v-2, v-1);
    

    ...just change that one line, above.  To test, enable "Backface Culling" in the viewport "Options" menu.. if your head looks "inside-out" then the polygons are facing the wrong way (inverted winding-order).  If they look correct, then you need to change the UV-polygon winding-order instead...

      
          Edge* e1 = edges[v-1];
          Edge* e2 = edges[v-2];
          Edge* e3 = edges[v-3];
    

    ...in either case, just make sure that they use the same winding-order... your code above is broke in that regard.


Log in to reply