VisUtils.cpp

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#include "stdafx.h"

namespace VisUtils {
    void PrepareFFTChunk(audio_chunk const & source, audio_chunk & out, double centerOffset) {
        const t_uint32 channels = source.get_channel_count();
        const t_uint32 sampleRate = source.get_sample_rate();
        FB2K_DYNAMIC_ASSERT( sampleRate > 0 );
        out.set_channels(channels, source.get_channel_config());
        out.set_sample_rate(sampleRate);
        const t_size inSize = source.get_sample_count();
        const t_size fftSize = MatchFFTSize(inSize);
        out.set_sample_count(fftSize);
        out.set_data_size(fftSize * channels);
        if (fftSize >= inSize) { //rare case with *REALLY* small input
            pfc::memcpy_t( out.get_data(), source.get_data(), inSize * channels );
            pfc::memset_null_t( out.get_data() + inSize * channels, (fftSize - inSize) * channels );
        } else { //inSize > fftSize, we're using a subset of source chunk for the job, pick a subset around centerOffset.
            const double baseOffset = pfc::max_t<double>(0, centerOffset - 0.5 * (double)fftSize / (double)sampleRate);
            const t_size baseSample = pfc::min_t<t_size>( (t_size) audio_math::time_to_samples(baseOffset, sampleRate), inSize - fftSize);
            pfc::memcpy_t( out.get_data(), source.get_data() + baseSample * channels, fftSize * channels);
        }
    }

    bool IsValidFFTSize(t_size p_size) {
        return p_size >= 2 && (p_size & (p_size - 1)) == 0;
    }

    t_size MatchFFTSize(t_size samples) {
        if (samples <= 2) return 2;
        t_size mask = 1;
        while(!IsValidFFTSize(samples)) {
            samples &= ~mask; mask <<= 1;
        }
        return samples;
    }
};