/* We use the weight tree pre-evaluation to weight the closures.
 * There is no need for the Closure type. */
struct Closure {
  float dummy;
};
#define CLOSURE_DEFAULT Closure(0.0)
#define closure_add(a, b) CLOSURE_DEFAULT
#define closure_mix(a, b, c) CLOSURE_DEFAULT

/* Store weight in red channel. Store negative to differentiate with evaluated closure. */
void closure_weight_add(inout ClosureDiffuse closure, float weight)
{
  closure.color.r -= weight;
}
void closure_weight_add(inout ClosureReflection closure, float weight)
{
  closure.color.r -= weight;
}
void closure_weight_add(inout ClosureRefraction closure, float weight)
{
  closure.color.r -= weight;
}

/* Create a random threshold inside the weight range. */
void closure_weight_randomize(inout ClosureDiffuse closure, float randu)
{
  closure.color.g = closure.color.r * randu;
}
void closure_weight_randomize(inout ClosureReflection closure, float randu)
{
  closure.color.g = closure.color.r * randu;
}
void closure_weight_randomize(inout ClosureRefraction closure, float randu)
{
  closure.color.g = closure.color.r * randu;
}

bool closure_weight_threshold(inout ClosureDiffuse closure, inout float weight)
{
  /* Decrement weight from random threshold. */
  closure.color.g += weight;
  /* Evaluate this closure if threshold reaches 0. */
  if (closure.color.g >= 0.0) {
    /* Returns the sum of all weights. */
    weight = abs(closure.color.r);
    return true;
  }
  return false;
}
bool closure_weight_threshold(inout ClosureReflection closure, inout float weight)
{
  closure.color.g += weight;
  if (closure.color.g >= 0.0) {
    weight = abs(closure.color.r);
    return true;
  }
  return false;
}
bool closure_weight_threshold(inout ClosureRefraction closure, inout float weight)
{
  closure.color.g += weight;
  if (closure.color.g >= 0.0) {
    weight = abs(closure.color.r);
    return true;
  }
  return false;
}