/// <summary>
/// Generates several sub graphs with progressively fewer number of data points
/// This allows us to redraw the graph quickly during manipulation
/// </summary>
private void GenerateSubGraphs()
{
if (GraphData != null)
{
// Determine how many sub graphs we need
int numGraphs = 1;
int currNumPoints = GraphData.Count;
while (currNumPoints > 64)
{
currNumPoints = currNumPoints >> 1;
numGraphs++;
}
// Create empty sub graphs
graphData = new List <PointF> [numGraphs];
currNumPoints = GraphData.Count;
for (int i = 0; i < graphData.Length; i++)
{
graphData[i] = new List <PointF>(currNumPoints);
currNumPoints = currNumPoints % 2 == 0 ? currNumPoints >> 1 : currNumPoints >> 1 + 1;
}
// This is the source of the graph's efficiency, here we take the users input and generate several other
// data inputs with progressively less accurate (due to rounding) depictions of the graph data, but each
// with 1/2 as many points as the last graph we generated.
float[] totalX = new float[graphData.Length];
float[] totalY = new float[graphData.Length];
float lastX = float.MinValue;
for (int i = 0; i < GraphData.Count; i++)
{
IGraphData point = GraphData[i];
float x = (float)point.GetX();
float y = (float)WorldToScreenYCoord(point.GetY());
bool isLastPoint = i == GraphData.Count - 1;
if (x < lastX)
{
throw new ArgumentException("GraphData must be sorted by ascending X values");
}
lastX = x;
// Add the first and last points to all graphData sets
if (i == 0)
{
for (int j = 1; j < graphData.Length; j++)
{
graphData[j].Add(new PointF(x, y));
}
}
graphData[0].Add(new PointF(x, y)); // Add all data points to the first graphData set
for (int j = 1; j < graphData.Length; j++) // For the rest of the sets, add averages of the points
{
totalX[j] += x;
totalY[j] += y;
// We are dealing with powers of 2, so we can do a more efficient mod operation '%'
int mask = (1 << j) - 1;
int remainder = (mask & i);
if (remainder == 0 || isLastPoint)
{
int divisor = remainder == 0 ? mask + 1 : remainder;
graphData[j].Add(new PointF(totalX[j] / divisor, totalY[j] / divisor));
totalX[j] = totalY[j] = 0;
}
}
}
}
}
