17-07-03_wav_speed_rendering

High Speed Graphing of High Density Linear Data

Accelerated Graphing for Linear Signals

I dramatically sped-up the graphing by drawing only single vertical lines (of small range min and max values) when the point density exceeds the horizontal pixel density. This is only suitable for evenly-spaced linear data (which is exactly what my target applications will be plotting). Performance is great, and there is plenty of room for improvement on the coding side too. AddLineXY() will be used to manually draw a line between every X,Y point in a list. AddLineSignal() graphs data from huge amounts of linear data by only graphing vertical lines.

I'm getting ~50 Hz frame rate plotting about 1 million data points:

Load Data from WAV File

Rather than generating fake data, let's use some real data. A ~20 second 8-bit 44100Hz WAV (/data/8bit_mono.wav) has about 780k data points. The WAV PCM sound file format is pretty simple. I wish every analog data recording file format had such a simple, easy-to-use, and well-documented header... pCLAMP -_-

Function Reference

Reading a WAV File using a Byte Array

this only works as written for 8-bit WAV files

byte[] bytes = System.IO.File.ReadAllBytes(filename);
Ys = new List<double>();
for (int i=44; i<bytes.Length; i++) {Ys.Add((double)bytes[i]);}

AddLineSignal()

public void AddLineSignal(List<double> Ys, double unitsPerPoint = 10, double offsetX = 0,  bool drawGrid = true)
{
	double unitsPerPixel = AX.UnitsPerPxX;
	double iPerPixel = unitsPerPixel / unitsPerPoint;
	double nDataPixels = unitsPerPoint * Ys.Count / unitsPerPixel;
	double offsetPixels = -(AX.GetAxis()[0] - offsetX) / unitsPerPixel;
	List<Point> points = new List<Point>();
	for (int x = 0; x < dataSizeX; x++)
	{
		int iLeft = (int)((iPerPixel * ((x + 0) - offsetPixels)));
		int iRight = (int)((iPerPixel * ((x + 1) - offsetPixels)));
		if ((iLeft < 0) || (iRight <= 0)) continue;
		if (iRight > Ys.Count) continue;
		if (iRight - iLeft == 0) continue;
		double colMin = Ys.GetRange(iLeft, iRight - iLeft).Min();
		double colMax = Ys.GetRange(iLeft, iRight - iLeft).Max();
		colMin = (colMin - AX.GetAxis()[2]) * AX.pxPerUnitY;
		colMax = (colMax - AX.GetAxis()[2]) * AX.pxPerUnitY;
		points.Add(new Point(x, (int)colMin));
		if ((int)colMin != (int)colMax) { points.Add(new Point(x, (int)colMax)); }
	}
	graphicsData.DrawLines(new Pen(Color.Red, 1), points.ToArray()); 
	dataPointCount = Ys.Count;
	dataLinesCount = points.Count;
}