private static int GenerateBitmap(FastBitmap bmp, byte[] buf, List <Color> fourColors)
{
int w = bmp.Width;
int h = bmp.Height;
int nibbleOffset = 0;
var nibbleEnd = buf.Length * 2;
var x = 0;
var y = 0;
for (; ;)
{
if (nibbleOffset >= nibbleEnd)
{
return(-1);
}
var v = GetNibble(buf, nibbleOffset++);
if (v < 0x4)
{
v = (v << 4) | GetNibble(buf, nibbleOffset++);
if (v < 0x10)
{
v = (v << 4) | GetNibble(buf, nibbleOffset++);
if (v < 0x040)
{
v = (v << 4) | GetNibble(buf, nibbleOffset++);
if (v < 4)
{
v |= (w - x) << 2;
}
}
}
}
var len = v >> 2;
if (len > w - x)
{
len = w - x;
}
var color = v & 0x03;
if (color > 0)
{
var c = fourColors[color];
bmp.SetPixel(x, y, c, len);
}
x += len;
if (x >= w)
{
y++;
if (y >= h)
{
break;
}
x = 0;
nibbleOffset += (nibbleOffset & 1);
}
}
return(0);
}
public Bitmap Draw(double[] samples)
{
int width = samples.Length / _nfft;
int height = _nfft / 2;
var bmp = new FastBitmap(new Bitmap(width, height));
bmp.LockImage();
for (int x = 0; x < width; x++)
{
// read a segment of the recorded signal
for (int i = 0; i < _nfft; i++)
{
_segment[i] = samples[x * _nfft + i] * _window[i];
}
// transform to the frequency domain
_fft.ComputeForward(_segment);
// compute the magnitude of the spectrum
MagnitudeSpectrum(_segment, _magnitude);
// draw
for (int y = 0; y < height; y++)
{
int colorIndex = _mapper.Map(_magnitude[y]);
bmp.SetPixel(x, height - y - 1, _palette[colorIndex]);
}
}
bmp.UnlockImage();
return(bmp.GetBitmap());
}
public Bitmap Draw(double[] samples)
{
int width = samples.Length / _nfft;
int height = _nfft / 2;
var bmp = new FastBitmap(new Bitmap(width, height));
bmp.LockImage();
for (int x = 0; x < width; x++)
{
// process 2 segments offset by -1/4 and 1/4 fft size, resulting in 1/2 fft size
// window spacing (the minimum overlap to avoid discarding parts of the signal)
ProcessSegment(samples, (x * _nfft) - (x > 0 ? _nfft / 4 : 0), _magnitude1);
ProcessSegment(samples, (x * _nfft) + (x < width - 1 ? _nfft / 4 : 0), _magnitude2);
// draw
for (int y = 0; y < height; y++)
{
int colorIndex = _mapper.Map((_magnitude1[y] + _magnitude2[y]) / 2.0);
bmp.SetPixel(x, height - y - 1, _palette[colorIndex]);
}
}
bmp.UnlockImage();
return(bmp.GetBitmap());
}