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* libscopeprotocols                                                                                                    *
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* Copyright (c) 2012-2024 Andrew D. Zonenberg and contributors                                                         *
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#include "../scopehal/scopehal.h"
#include "DownsampleFilter.h"

using namespace std;

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Construction / destruction

DownsampleFilter::DownsampleFilter(const string& color)
	: Filter(color, CAT_MATH)
{
	AddStream(Unit(Unit::UNIT_VOLTS), "data", Stream::STREAM_TYPE_ANALOG);
	CreateInput("RF");

	m_factorname = "Downsample Factor";
	m_parameters[m_factorname] = FilterParameter(FilterParameter::TYPE_INT, Unit(Unit::UNIT_COUNTS));
	m_parameters[m_factorname].SetIntVal(10);

	m_aaname = "Antialiasing Filter";
	m_parameters[m_aaname] = FilterParameter(FilterParameter::TYPE_BOOL, Unit(Unit::UNIT_COUNTS));
	m_parameters[m_aaname].SetBoolVal(1);
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Factory methods

bool DownsampleFilter::ValidateChannel(size_t i, StreamDescriptor stream)
{
	if(stream.m_channel == NULL)
		return false;

	if( (i == 0) && (stream.GetType() == Stream::STREAM_TYPE_ANALOG) )
		return true;

	return false;
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Accessors

string DownsampleFilter::GetProtocolName()
{
	return "Downsample";
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Actual decoder logic

void DownsampleFilter::Refresh()
{
	if(!VerifyAllInputsOKAndUniformAnalog())
	{
		SetData(NULL, 0);
		return;
	}

	//Get the input data
	auto din = dynamic_cast<UniformAnalogWaveform*>(GetInputWaveform(0));
	size_t len = din->m_samples.size();

	//Propagate units
	m_streams[0].m_yAxisUnit = GetInput(0).GetYAxisUnits();

	//Set up output waveform and get configuration
	int64_t factor = m_parameters[m_factorname].GetIntVal();
	if (factor == 0)
	{
		// Occurs momentarily while editing the value sometimes in glscopeclient
		return;
	}

	size_t outlen = len / factor;
	auto cap = SetupEmptyUniformAnalogOutputWaveform(din, 0);
	cap->Resize(outlen);

	cap->PrepareForCpuAccess();
	din->PrepareForCpuAccess();

	//Default path with antialiasing filter
	if(m_parameters[m_aaname].GetBoolVal())
	{
		//Cut off all frequencies shorter than our decimation factor
		float cutoff_period = factor;
		float sigma = cutoff_period / sqrt(2 * log(2));
		int kernel_radius = ceil(3*sigma);

		//Generate the actual Gaussian kernel
		int kernel_size = kernel_radius*2 + 1;
		vector<float> kernel;
		kernel.resize(kernel_size);
		float alpha = 1.0f / (sigma * sqrt(2*M_PI));
		for(int x=0; x < kernel_size; x++)
		{
			int delta = (x - kernel_radius);
			kernel[x] = alpha * exp(-delta*delta/(2*sigma));
		}
		float sum = 0;
		for(auto k : kernel)
			sum += k;
		for(int i=0; i<kernel_size; i++)
			kernel[i] /= sum;

		//Do the actual downsampling.
		for(size_t i=0; i<outlen; i++)
		{
			//Do the convolution
			float conv = 0;
			ssize_t base = i*factor;
			for(ssize_t delta = -kernel_radius; delta <= kernel_radius; delta ++)
			{
				ssize_t pos = base + delta;
				if( (pos < 0) || (pos >= (ssize_t)len) )
					continue;

				conv += din->m_samples[pos] * kernel[delta + kernel_radius];
			}

			//Do the actual decimation
			cap->m_samples[i] 	= conv;
		}
	}

	//Optimized path with no AA if the input is known to not contain any higher frequency content
	else
	{
		for(size_t i=0; i<outlen; i++)
			cap->m_samples[i]	= din->m_samples[i*factor];
	}

	//Copy our time scales from the input
	cap->m_timescale = din->m_timescale * factor;
	cap->MarkModifiedFromCpu();
}
