private async void DrawSpectrogram()
{
if (_bitmap == null)
{
return;
}
// stop here if a drawing operation is already in progress
if (_isDrawing)
{
_isRequested = true;
return;
}
// set the drawing flag
_isDrawing = true;
// preprocess the data to draw
var mapped = Data.Where(p => p.Y is double[]).Select(p => new Tuple <double, double[]>(AxisX.GetItemPixel(p.X), (double[])p.Y)).OrderBy(p => p.Item1).ToList();
var palette = ColorPalette;
// lock the backbuffer
var bitmap = _bitmap;
bitmap.Lock();
var width = bitmap.PixelWidth;
var height = bitmap.PixelHeight;
var stride = bitmap.BackBufferStride;
var backbuffer = bitmap.BackBuffer;
// fill the backbuffer from a background thread
await Task.Run(() =>
{
// map data points to axis pixels
if (mapped.Count > 0)
{
var rows = mapped.First().Item2.Length;
var rowHeight = height / (double)rows;
var maximumValue = mapped.Aggregate(new double[rows], (c, p) =>
{
for (var i = 0; i < c.Length; i++)
{
c[i] = Math.Max(c[i], p.Item2[i]);
}
return(c);
});
// iterate over all pixels in the series
var lastColumn = 0;
var nextColumn = 1;
for (var x = 0.0; x < width; x++)
{
// find the next data column
while (nextColumn < mapped.Count - 1 && x > mapped[nextColumn].Item1)
{
lastColumn = nextColumn;
nextColumn += 1;
}
// calculate the horizontal relative position in between the two columns
var factorX = (x - mapped[lastColumn].Item1) / (mapped[nextColumn].Item1 - mapped[lastColumn].Item1);
// draw the column
var lastRow = 0;
var nextRow = 1;
for (var y = 0.0; y < height; y++)
{
// find the next data row
while (nextRow < mapped[nextColumn].Item2.Length - 1 && y > nextRow * rowHeight)
{
lastRow = nextRow;
nextRow += 1;
}
// calculate the horizontal relative position in between the two rows
var factorY = (y - lastRow * rowHeight) / rowHeight;
// interpolate the point value
double c;
if (factorX >= 0 && factorX <= 1 && factorY >= 0 && factorY <= 1)
{
var a00 = mapped[lastColumn].Item2[lastRow];
var a10 = mapped[nextColumn].Item2[lastRow] - mapped[lastColumn].Item2[lastRow];
var a01 = mapped[lastColumn].Item2[nextRow] - mapped[lastColumn].Item2[lastRow];
var a11 = mapped[nextColumn].Item2[nextRow] + mapped[lastColumn].Item2[lastRow] - (mapped[nextColumn].Item2[lastRow] + mapped[lastColumn].Item2[nextRow]);
c = a00 + a10 * factorX + a01 * factorY + a11 * factorX * factorY;
}
else
{
c = 0;
}
// scale the pixel value to 0..1
var scaledMaximum = factorY * (maximumValue[nextRow] - maximumValue[lastRow]) + maximumValue[lastRow];
var scaledValue = scaledMaximum > 1e-3 ? c / scaledMaximum : 0;
// get the color for the pixel
var color = palette[(int)(scaledValue * (palette.Count - 1))];
// draw the pixel
var value = (byte)(255 * scaledValue);
unsafe
{
var address = (byte *)(backbuffer + ((int)(height - 1 - y) * stride) + (int)x * 4);
*(address++) = color.B;
*(address++) = color.G;
*(address++) = color.R;
*(address++) = color.A;
}
}
}
}
else
{
var color = palette[0];
for (var i = 0; i < width *height * 4; i += 4)
{
unsafe
{
var address = (byte *)(backbuffer + i);
*(address++) = color.B;
*(address++) = color.G;
*(address++) = color.R;
*(address++) = color.A;
}
}
}
});
// write the bitmap contents
bitmap.AddDirtyRect(new Int32Rect(0, 0, width, height));
bitmap.Unlock();
// invalidate visuals to redraw
_isDrawing = false;
InvalidateVisual();
if (_isRequested)
{
_isRequested = false;
DrawSpectrogram();
}
}