   return v;
 }
 
-__global__ float3 add(float3 a, float3 b){
+__device__ float3 add(float3 a, float3 b){
   a.x += b.x;
   a.y += b.y;
   a.z += b.z;


  int x = -IMAGE_DIM/2 + blockIdx.x * blockDim.x + threadIdx.x;
  int y = -IMAGE_DIM/2 + blockIdx.y * blockDim.y + threadIdx.y;

  // For each pixel 


  return c;
}

__device__ float3 normalize(float3 v){
  float l = sqrt(v.x*v.x + v.y*v.y + v.z*v.z);
  v.x /= l;
  v.y /= l;
