Getting rid of "acne" on high-triangle models?

I'm having the same problem. My rabbit looks horrible; I used the one Jamis referred to. My current debugging technique is to set the default background color to Hot Pink and then I am setting all shadows to Lime Green. I wish I could post the picture but all the acne got replaced with lime green colors which tells me the problem is definitely having to do with shadows; specifically OverPoint. I don't know why this is happening since the math and algorithms are just as described in the book and pass all the tests. I am using C# so perhaps it is the .NET VM if that is happening. I have some ideas and I will check back if anything works but I do recommend changing the colors as I described to help isolate where the acne is actually coming from.

Here is a code sample from Material.Lighting:


if ((lightDotNormal < 0) || inShadow)
{
diffuse = inShadow ? Color.LimeGreen : Color.Black;
specular = inShadow ? Color.LimeGreen : Color.Black;
}
else
{

The solution I came up with is surprising... I had to stop letting the object shadow itself. My solution involved two things:
1) Make sure the hit object is not the same as the object being tested i.e. (hit.Object != obj)
2) Make sure the direction of the shadow vector isn't hitting the wrong side of the shape, in this case a triangle i.e. (Ray Direction DOT Normal Vector) > 0

I changed IsShadowed called from ShadeHit in the World class. Instead of passing in the OverPoint I am now passing the whole Computations object:


       public bool IsShadowed(RTObject obj, Computations comps)

       {

           bool isShadowed = false;

           var point = comps.OverPoint;



           foreach (var light in Lights)

           {

               var v = new Vector(light.Position - point);

               var distance = v.Magnitude;

               var direction = v.Normalize;



               var r = new Ray(point, direction);

               var intersections = Intersect(r);



               var dN = direction.Dot(comps.NormalVector);

               var h = intersections.Hit;



               if ((h != null) && (h.t < distance) && (h.Object.HasShadow) && (h.Object != obj) && (dN <= 0))

               {

                   isShadowed = true;

                   break;

               }

           }



           return isShadowed;

       }