-#ifdef INTERP_INDEX
- span.interpMask |= SPAN_INDEX;
- if (ctx->Light.ShadeModel == GL_SMOOTH) {
- GLfloat eMaj_di = vMax->attrib[FRAG_ATTRIB_CI][0] - vMin->attrib[FRAG_ATTRIB_CI][0];
- GLfloat eBot_di = vMid->attrib[FRAG_ATTRIB_CI][0] - vMin->attrib[FRAG_ATTRIB_CI][0];
- didx = oneOverArea * (eMaj_di * eBot.dy - eMaj.dy * eBot_di);
- didy = oneOverArea * (eMaj.dx * eBot_di - eMaj_di * eBot.dx);
- span.indexStep = SignedFloatToFixed(didx);
- }
- else {
- span.interpMask |= SPAN_FLAT;
- didx = didy = 0.0F;
- span.indexStep = 0;
- }
-#endif