question

Until there's an AnswerHub fix for their sites (it's a known, new bug with their service) here's a copy of Matthew's answer:

Here is the logic we are currently using to determine the color of each node of the A* grid when we draw the heat map.

First we calculate a weight value based off the mode the user selects:

// Traversals Per Time
weight = traversals / statisticaltime();

// Average Blockage Time per Traversal
weight = totalBlockedTime / max(1, traversals);

// Percent of Total Time Blocked
weight = 100.0 * totalBlockedTime / statisticaltime();

// Percent of Total Traversals
weight = 100.0 * traversals / heatMapTotalTraversals;

Then we divide that weight value by the Max Heat Value the user specifies:

weight /= navigator->maxHeatValue;
weight = max(0, weight);
weight = min(0.9999, weight);

We now have a number between 0 and 1. Now we multiply this number by the number of colors in our color progression to figure out what color to paint.

double progressionFactor = (double)(heatMapColorProgression.size() - 1) * weight;
Vec4f lowColor = heatMapColorProgression[(int)floor(progressionFactor)];
Vec4f highColor = heatMapColorProgression[(int)ceil(progressionFactor)];
Vec4f color = lowColor + ((highColor - lowColor) * frac(progressionFactor));

And for reference these are the color progression colors:

std::vector<Vec4f> AStarNavigator::heatMapColorProgression =
{
Vec4f(0.110f, 0.280f, 0.467f, 1.0f),
Vec4f(0.106f, 0.541f, 0.353f, 1.0f),
Vec4f(0.984f, 0.690f, 0.129f, 1.0f),
Vec4f(0.964f, 0.533f, 0.220f, 1.0f),
Vec4f(0.933f, 0.243f, 0.196f, 1.0f)
};