/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Sonic Visualiser
    An audio file viewer and annotation editor.
    Centre for Digital Music, Queen Mary, University of London.
    This file copyright 2006-2016 Chris Cannam and QMUL.
    
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2 of the
    License, or (at your option) any later version.  See the file
    COPYING included with this distribution for more information.
*/

#include "Colour3DPlotRenderer.h"
#include "RenderTimer.h"

#include "base/Profiler.h"
#include "base/HitCount.h"

#include "data/model/DenseThreeDimensionalModel.h"
#include "data/model/Dense3DModelPeakCache.h"
#include "data/model/FFTModel.h"

#include "LayerGeometryProvider.h"
#include "VerticalBinLayer.h"
#include "PaintAssistant.h"
#include "ImageRegionFinder.h"

#include "view/ViewManager.h" // for main model sample rate. Pity

#include <vector>

#include <utility>
namespace sv {

using namespace std::rel_ops;

//#define DEBUG_COLOUR_PLOT_REPAINT 1
//#define DEBUG_COLOUR_PLOT_CACHE_SELECTION 1

using namespace std;

static vector<QRgb>
makeColourmap(const Colour3DPlotRenderer::Parameters &parameters)
{
    vector<QRgb> colourmap;
    colourmap.reserve(256);
    for (int pixel = 0; pixel < 256; ++pixel) {
        QColor c = parameters.colourScale.getColourForPixel
            (pixel, parameters.colourRotation);
        if (!parameters.opaque) {
            c.setAlpha(20 + (pixel * 220) / 256);
        }
        colourmap.push_back(c.rgba());
    }
    return colourmap;
}

Colour3DPlotRenderer::Colour3DPlotRenderer(Sources sources,
                                           Parameters parameters) :
    m_sources(sources),
    m_params(parameters),
    m_colourmap(makeColourmap(parameters)),
    m_secondsPerXPixel(0.0),
    m_secondsPerXPixelValid(false)
{
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "Colour3DPlotRenderer[" << this << "]::Colour3DPlotRenderer("
            << m_sources.source << ")" << endl;
#endif
}

Colour3DPlotRenderer::~Colour3DPlotRenderer()
{
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "Colour3DPlotRenderer[" << this << "]::~Colour3DPlotRenderer()"
            << endl;
#endif
}

Colour3DPlotRenderer::RenderResult
Colour3DPlotRenderer::render(const LayerGeometryProvider *v, QPainter &paint, QRect rect)
{
    return render(v, paint, rect, false);
}

Colour3DPlotRenderer::RenderResult
Colour3DPlotRenderer::renderTimeConstrained(const LayerGeometryProvider *v,
                                            QPainter &paint, QRect rect)
{
    return render(v, paint, rect, true);
}

QRect
Colour3DPlotRenderer::getLargestUncachedRect(const LayerGeometryProvider *v)
{
    RenderType renderType = decideRenderType(v);

    if (renderType == DirectTranslucent) {
        return QRect(); // never cached
    }

    int h = m_cache.getSize().height();

    QRect areaLeft(0, 0, m_cache.getValidLeft(), h);
    QRect areaRight(m_cache.getValidRight(), 0,
                    m_cache.getSize().width() - m_cache.getValidRight(), h);

    if (areaRight.width() > areaLeft.width()) {
        return areaRight;
    } else {
        return areaLeft;
    }
}

bool
Colour3DPlotRenderer::geometryChanged(const LayerGeometryProvider *v)
{
    RenderType renderType = decideRenderType(v);

    if (renderType == DirectTranslucent) {
        return true; // never cached
    }

    // Use getRawZoomLevel to pass to the cache, because the scaled
    // version (getRoundedZoomLevel) does not always correctly
    // indicate a change in zoom
    if (m_cache.getSize() == v->getPaintSize() &&
        m_cache.getZoomLevel() == v->getRawZoomLevel() &&
        m_cache.getStartFrame() == v->getStartFrame()) {
        return false;
    } else {
        return true;
    }
}

Colour3DPlotRenderer::RenderResult
Colour3DPlotRenderer::render(const LayerGeometryProvider *v,
                             QPainter &paint, QRect rect, bool timeConstrained)
{
    RenderType renderType = decideRenderType(v);

    if (timeConstrained) {
        if (renderType != DrawBufferPixelResolution) {
            // Rendering should be fast in bin-resolution and direct
            // draw cases because we are quite well zoomed-in, and the
            // sums are easier this way. Calculating boundaries later
            // will be fiddly for partial paints otherwise.
            timeConstrained = false;
        }
    }
            
    int x0 = v->getXForViewX(rect.x());
    int x1 = v->getXForViewX(rect.x() + rect.width());
    if (x0 < 0) x0 = 0;
    if (x0 > v->getPaintWidth()) x0 = v->getPaintWidth();
    if (x1 < 0) x1 = 0;
    if (x1 > v->getPaintWidth()) x1 = v->getPaintWidth();

    sv_frame_t startFrame = v->getStartFrame();

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": rect is " << rect.x() << "," << rect.y()
            << " " << rect.width() << "x" << rect.height() << "; paint width = "
            << v->getPaintWidth() << ", x0 = " << x0 << ", x1 = " << x1
            << endl;
#endif

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": cache size is " << m_cache.getSize().width()
            << "x" << m_cache.getSize().height()
            << " at raw zoom level " << m_cache.getZoomLevel()
            << endl;
#endif

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    {
        bool justCreated = m_cache.getSize().isEmpty();
        bool justInvalidated =
            (m_cache.getSize() != v->getPaintSize() ||
             m_cache.getZoomLevel() != v->getRawZoomLevel());
        SVDEBUG << "render " << m_sources.source
                << ": justCreated = " << justCreated
                << ", justInvalidated = " << justInvalidated
                << endl;
    }
#endif
    
    m_cache.resize(v->getPaintSize());
    m_cache.setZoomLevel(v->getRawZoomLevel());

    m_magCache.resize(v->getPaintSize().width());
    m_magCache.setZoomLevel(v->getRawZoomLevel());
    
    if (renderType == DirectTranslucent) {
        MagnitudeRange range = renderDirectTranslucent(v, paint, rect);
        return { rect, range };
    }
    
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": cache start " << m_cache.getStartFrame()
            << " valid left " << m_cache.getValidLeft()
            << " valid right " << m_cache.getValidRight()
            << endl;
    SVDEBUG << "render " << m_sources.source
            << ": view start " << startFrame
            << " x0 " << x0
            << " x1 " << x1
            << endl;
#endif

    static HitCount count("Colour3DPlotRenderer: image cache");

    if (m_cache.isValid()) { // some part of the cache is valid

        if (v->getXForFrame(m_cache.getStartFrame()) ==
            v->getXForFrame(startFrame) &&
            m_cache.getValidLeft() <= x0 &&
            m_cache.getValidRight() >= x1) {

#ifdef DEBUG_COLOUR_PLOT_REPAINT
            SVDEBUG << "render " << m_sources.source
                    << ": cache hit" << endl;
#endif
            count.hit();
            
            // cache is valid for the complete requested area
            paint.drawImage(rect, m_cache.getImage(), rect);

            MagnitudeRange range = m_magCache.getRange(x0, x1 - x0);

            return { rect, range };

        } else {
#ifdef DEBUG_COLOUR_PLOT_REPAINT
            SVDEBUG << "render " << m_sources.source
                    << ": cache partial hit" << endl;
#endif
            count.partial();
            
            // cache doesn't begin at the right frame or doesn't
            // contain the complete view, but might be scrollable or
            // partially usable
            m_cache.scrollTo(v, startFrame);
            m_magCache.scrollTo(v, startFrame);

            // if we are not time-constrained, then we want to paint
            // the whole area in one go; we don't return a partial
            // paint. To avoid providing the more complex logic to
            // handle painting discontiguous areas, if the only valid
            // part of cache is in the middle, just make the whole
            // thing invalid and start again.
            if (!timeConstrained) {
                if (m_cache.getValidLeft() > x0 &&
                    m_cache.getValidRight() < x1) {
                    m_cache.invalidate();
                }
            }
        }
    } else {
        // cache is completely invalid
#ifdef DEBUG_COLOUR_PLOT_REPAINT
        SVDEBUG << "render " << m_sources.source
                << ": cache miss" << endl;
#endif
        count.miss();
        m_cache.setStartFrame(startFrame);
        m_magCache.setStartFrame(startFrame);
    }

    bool rightToLeft = false;

    int reqx0 = x0;
    int reqx1 = x1;
    
    if (!m_cache.isValid() && timeConstrained) {
        if (x0 == 0 && x1 == v->getPaintWidth()) {
            
            // When rendering the whole area, in a context where we
            // might not be able to complete the work, start from
            // somewhere near the middle so that the region of
            // interest appears first.
            //
            // This is very useful if we actually are slow to render,
            // but if we're not sure how fast we'll be, we should
            // prefer not to because it can be distracting to render
            // fast from the middle and then jump back to fill in the
            // start. That is:
            //
            // - if our seconds-per-x-pixel count is invalid, then we
            // don't do this: we've probably only just been created
            // and don't know how fast we'll be yet (this happens
            // often while zooming rapidly in and out). The exception
            // to the exception is if we're displaying peak
            // frequencies; this we can assume to be slow. (Note that
            // if the seconds-per-x-pixel is valid and we know we're
            // fast, then we've already set timeConstrained false
            // above so this doesn't apply)
            // 
            // - if we're using a peak cache, we don't do this;
            // drawing from peak cache is often (even if not always)
            // fast.

            bool drawFromTheMiddle = true;

            if (!m_secondsPerXPixelValid &&
                (m_params.binDisplay != BinDisplay::PeakFrequencies)) {
                drawFromTheMiddle = false;
            } else {
                int peakCacheIndex = -1, binsPerPeak = -1;
                getPreferredPeakCache(v, peakCacheIndex, binsPerPeak);
                if (peakCacheIndex >= 0) { // have a peak cache
                    drawFromTheMiddle = false;
                }
            }

            if (drawFromTheMiddle) {
                double offset = 0.5 * (double(rand()) / double(RAND_MAX));
                x0 = int(x1 * offset);
            }
        }
    }

    if (m_cache.isValid()) {
            
        // When rendering only a part of the cache, we need to make
        // sure that the part we're rendering is adjacent to (or
        // overlapping) a valid area of cache, if we have one. The
        // alternative is to ditch the valid area of cache and render
        // only the requested area, but that's risky because this can
        // happen when just waving the pointer over a small part of
        // the view -- if we lose the partly-built cache every time
        // the user does that, we'll never finish building it.
        int left = x0;
        int width = x1 - x0;
        bool isLeftOfValidArea = false;
        m_cache.adjustToTouchValidArea(left, width, isLeftOfValidArea);
        x0 = left;
        x1 = x0 + width;

        // That call also told us whether we should be painting
        // sub-regions of our target region in right-to-left order in
        // order to ensure contiguity
        rightToLeft = isLeftOfValidArea;
    }
    
    // Note, we always paint the full height to cache. We want to
    // ensure the cache is coherent without having to worry about
    // vertical matching of required and valid areas as well as
    // horizontal.

    if (renderType == DrawBufferBinResolution) {

        renderToCacheBinResolution(v, x0, x1 - x0);

    } else { // must be DrawBufferPixelResolution, handled DirectTranslucent earlier

/*!!! This is not desirable behaviour when using threaded repaint - we
      don't actually know for sure here whether we're doing that, but
      it is the default, and the worst case if we aren't is less bad
      than it used to be
  
        if (timeConstrained && !justCreated && justInvalidated) {
            SVDEBUG << "render " << m_sources.source
                    << ": invalidated cache in time-constrained context, that's all we're doing for now - wait for next update to start filling" << endl;
        } else {
*/
        
            renderToCachePixelResolution(v, x0, x1 - x0, rightToLeft, timeConstrained);
/*        } */
    }

    QRect pr = rect & m_cache.getValidArea();
    paint.drawImage(pr.x(), pr.y(), m_cache.getImage(),
                    pr.x(), pr.y(), pr.width(), pr.height());

    if (!timeConstrained && (pr != rect)) {
        QRect cva = m_cache.getValidArea();
        SVCERR << "WARNING: failed to render entire requested rect "
               << "even when not time-constrained: wanted "
               << rect.x() << "," << rect.y() << " "
               << rect.width() << "x" << rect.height() << ", got "
               << pr.x() << "," << pr.y() << " "
               << pr.width() << "x" << pr.height()
               << ", after request of width " << (x1 - x0)
               << endl
               << "(cache valid area is "
               << cva.x() << "," << cva.y() << " "
               << cva.width() << "x" << cva.height() << ")"
               << endl;
    }

    MagnitudeRange range = m_magCache.getRange(reqx0, reqx1 - reqx0);

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": returning rect rendered as " << pr.x() << "," << pr.y()
            << " " << pr.width() << "x" << pr.height() << endl;
    SVDEBUG << "render " << m_sources.source
            << ": mag range from cache in x-range " << reqx0
            << " to " << reqx1 << " is " << range.getMin() << " -> "
            << range.getMax() << endl;
#endif
    
    return { pr, range };
}

bool
Colour3DPlotRenderer::getBinResolutions(const LayerGeometryProvider *v,
                                        int &binResolution,
                                        double &renderBinResolution) const
{
    auto model = ModelById::getAs<DenseThreeDimensionalModel>(m_sources.source);
    if (!model || !v || !(v->getViewManager())) {
        binResolution = 1;
        renderBinResolution = 1.0;
        return false;
    }

    binResolution = model->getResolution();
    sv_samplerate_t modelRate = model->getSampleRate();

    double rateRatio = v->getViewManager()->getMainModelSampleRate() / modelRate;
    renderBinResolution = binResolution * rateRatio;

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "Colour3DPlotRenderer: binResolution " << binResolution
            << ", modelRate " << modelRate
            << ", main model rate " << v->getViewManager()->getMainModelSampleRate()
            << ", rateRatio " << rateRatio << ", renderBinResolution "
            << renderBinResolution << endl;
#endif

    return true;
}

Colour3DPlotRenderer::RenderType
Colour3DPlotRenderer::decideRenderType(const LayerGeometryProvider *v) const
{
    auto model = ModelById::getAs<DenseThreeDimensionalModel>(m_sources.source);
    if (!model || !v || !(v->getViewManager())) {
        return DrawBufferPixelResolution; // or anything
    }

    int binResolution;
    double renderBinResolution;
    if (!getBinResolutions(v, binResolution, renderBinResolution)) {
        return DrawBufferPixelResolution; // or anything
    }

    if (m_params.binDisplay == BinDisplay::PeakFrequencies) {
        // no alternative works here
#ifdef DEBUG_COLOUR_PLOT_REPAINT
        SVDEBUG << "decideRenderType: binDisplay is PeakFrequencies, must use pixel resolution" << endl;
#endif
        return DrawBufferPixelResolution;
    }

    ZoomLevel zoomLevel = v->getRoundedZoomLevel();

    if (!m_params.opaque && !m_params.interpolate) {

        // consider explicit translucent cell option -- only if not
        // smoothing & not requested opaque & sufficiently zoomed-in

        ZoomLevel threshold(ZoomLevel::FramesPerPixel,
                            int(round(renderBinResolution / 3)));
        
        if (model->getHeight() * 3 < v->getPaintHeight() &&
            zoomLevel < threshold) {
#ifdef DEBUG_COLOUR_PLOT_REPAINT
            SVDEBUG << "decideRenderType: zoomLevel " << zoomLevel
                    << " < threshold " << threshold
                    << " and not opaque or smoothed; "
                    << "using DirectTranslucent mode" << endl;
#endif
            return DirectTranslucent;
        }
    }

    ZoomLevel threshold(ZoomLevel::FramesPerPixel,
                        int(round(renderBinResolution)));

    if (zoomLevel < threshold) {
#ifdef DEBUG_COLOUR_PLOT_REPAINT
        SVDEBUG << "decideRenderType: zoomLevel " << zoomLevel
                << " < threshold " << threshold
                << ", drawing at bin resolution" << endl;
#endif
        return DrawBufferBinResolution;
    } else {
#ifdef DEBUG_COLOUR_PLOT_REPAINT
        SVDEBUG << "decideRenderType: zoomLevel " << zoomLevel
                << " >= threshold " << threshold
                << ", drawing at pixel resolution" << endl;
#endif
        return DrawBufferPixelResolution;
    }
}

ColumnOp::Column
Colour3DPlotRenderer::getColumn(int sx, int minbin, int nbins,
                                bool suppressCache,
                                shared_ptr<DenseThreeDimensionalModel> source) const
{
    Profiler profiler("Colour3DPlotRenderer::getColumn");

    // order:
    // get column -> scale -> normalise -> record extents ->
    // peak pick -> distribute/interpolate -> apply display gain

    // we do the first bit here:
    // get column -> scale -> normalise

    ColumnOp::Column column;
    
    if (m_params.showDerivative && sx > 0) {

        auto prev = getColumnRaw(sx - 1, minbin, nbins, suppressCache, source);
        column = getColumnRaw(sx, minbin, nbins, suppressCache, source);
        
        for (int i = 0; i < nbins; ++i) {
            column[i] -= prev[i];
        }

    } else {
        column = getColumnRaw(sx, minbin, nbins, suppressCache, source);
    }

    if (m_params.colourScale.getScale() == ColourScaleType::Phase &&
        !m_sources.fft.isNone()) {
        return column;
    } else {
        return ColumnOp::normalize(ColumnOp::applyGain(column,
                                                       m_params.scaleFactor),
                                   m_params.normalization);
    }
}

ColumnOp::Column
Colour3DPlotRenderer::getColumnRaw(int sx, int minbin, int nbins,
                                   bool suppressCache,
                                   shared_ptr<DenseThreeDimensionalModel> source) const
{
    Profiler profiler("Colour3DPlotRenderer::getColumnRaw");

    if (m_params.colourScale.getScale() == ColourScaleType::Phase) {
        auto fftModel = ModelById::getAs<FFTModel>(m_sources.fft);
        if (fftModel) {
            auto fullColumn = fftModel->getPhases(sx);
            return ColumnOp::Column(fullColumn.data() + minbin,
                                    fullColumn.data() + minbin + nbins);
        }
    }

    if (suppressCache) {
        auto fftModel = dynamic_cast<FFTModel *>(source.get());
        if (fftModel) {
            return fftModel->getColumnWithoutCache(sx, minbin, nbins);
        } else {
            return source->getColumn(sx, minbin, nbins);
        }
    } else {
        return source->getColumn(sx, minbin, nbins);
    }
}

MagnitudeRange
Colour3DPlotRenderer::renderDirectTranslucent(const LayerGeometryProvider *v,
                                              QPainter &paint,
                                              QRect rect)
{
    Profiler profiler("Colour3DPlotRenderer::renderDirectTranslucent");

    MagnitudeRange magRange;
    
    QPoint illuminatePos;
    bool illuminate = v->shouldIlluminateLocalFeatures
        (m_sources.verticalBinLayer, illuminatePos);

    auto model = ModelById::getAs<DenseThreeDimensionalModel>(m_sources.source);
    if (!model) return magRange;
    
    int x0 = rect.left();
    int x1 = x0 + rect.width();

    int h = v->getPaintHeight();

    sv_frame_t modelStart = model->getStartFrame();
    sv_frame_t modelEnd = model->getEndFrame();
    int modelResolution = model->getResolution();

    double rateRatio =
        v->getViewManager()->getMainModelSampleRate() / model->getSampleRate();

    // the s-prefix values are source, i.e. model, column and bin numbers
    int sx0 = int((double(v->getFrameForX(x0)) / rateRatio - double(modelStart))
                  / modelResolution);
    int sx1 = int((double(v->getFrameForX(x1)) / rateRatio - double(modelStart))
                  / modelResolution);

    int sh = model->getHeight();

    const int buflen = 40;
    char labelbuf[buflen];

    int minbin = m_sources.verticalBinLayer->getIBinForY(v, h);
    if (minbin >= sh) minbin = sh - 1;
    if (minbin < 0) minbin = 0;
    
    int nbins  = m_sources.verticalBinLayer->getIBinForY(v, 0) - minbin + 1;
    if (minbin + nbins > sh) nbins = sh - minbin;

    int psx = -1;

    ColumnOp::Column preparedColumn;

    int modelWidth = model->getWidth();

    for (int sx = sx0; sx <= sx1; ++sx) {

        if (sx < 0 || sx >= modelWidth) {
            continue;
        }

        if (sx != psx) {

            // order:
            // get column -> scale -> normalise -> record extents ->
            // peak pick -> distribute/interpolate -> apply display gain

            // this does the first three:
            preparedColumn = getColumn(sx, minbin, nbins, false, model);
            
            magRange.sample(preparedColumn);

            if (m_params.binDisplay == BinDisplay::PeakBins) {
                preparedColumn = ColumnOp::peakPick(preparedColumn);
            }

            // Display gain belongs to the colour scale and is
            // applied by the colour scale object when mapping it

            psx = sx;
        }

        sv_frame_t fx = sx * modelResolution + modelStart;

        if (fx + modelResolution <= modelStart || fx > modelEnd) continue;

        int rx0 = v->getXForFrame(int(double(fx) * rateRatio));
        int rx1 = v->getXForFrame(int(double(fx + modelResolution + 1) * rateRatio));

        int rw = rx1 - rx0;
        if (rw < 1) rw = 1;

        bool showLabel = (rw > 10 &&
                          paint.fontMetrics().horizontalAdvance("0.000000") < rw - 3 &&
                          paint.fontMetrics().height() < (h / sh));
        
        for (int sy = minbin; sy < minbin + nbins; ++sy) {

            int ry0 = m_sources.verticalBinLayer->getIYForBin(v, sy);
            int ry1 = m_sources.verticalBinLayer->getIYForBin(v, sy + 1);

            if (m_params.invertVertical) {
                ry0 = h - ry0 - 1;
                ry1 = h - ry1 - 1;
            }
                    
            QRect r(rx0, ry1, rw, ry0 - ry1);

            float value = preparedColumn[sy - minbin];
            QColor colour = m_params.colourScale.getColour
                (value, m_params.colourRotation);

            if (rw == 1) {
                paint.setPen(colour);
                paint.setBrush(Qt::NoBrush);
                paint.drawLine(r.x(), r.y(), r.x(), r.y() + r.height() - 1);
                continue;
            }

            QColor brush(colour);

            if (rw > 3 && r.height() > 3) {
                brush.setAlpha(160);
            }

            paint.setPen(Qt::NoPen);
            paint.setBrush(brush);

            if (illuminate) {
                if (r.contains(illuminatePos)) {
                    paint.setPen(v->getForeground());
                }
            }
            
#ifdef DEBUG_COLOUR_PLOT_REPAINT
//            SVDEBUG << "rect " << r.x() << "," << r.y() << " "
//                      << r.width() << "x" << r.height() << endl;
#endif

            paint.drawRect(r);

            if (showLabel) {
                double value = model->getValueAt(sx, sy);
                snprintf(labelbuf, buflen, "%06f", value);
                QString text(labelbuf);
                PaintAssistant::drawVisibleText
                    (v,
                     paint,
                     rx0 + 2,
                     ry0 - h / sh - 1 + 2 + paint.fontMetrics().ascent(),
                     text,
                     PaintAssistant::OutlinedText);
            }
        }
    }

    return magRange;
}

void
Colour3DPlotRenderer::getPreferredPeakCache(const LayerGeometryProvider *v,
                                            int &peakCacheIndex,
                                            int &binsPerPeak) const
{
    peakCacheIndex = -1;
    binsPerPeak = -1;

    auto model = ModelById::getAs<DenseThreeDimensionalModel>(m_sources.source);
    if (!model) return;
    if (m_params.binDisplay == BinDisplay::PeakFrequencies) return;
    if (m_params.colourScale.getScale() == ColourScaleType::Phase) return;
    
    ZoomLevel zoomLevel = v->getRoundedZoomLevel();
    int binResolution;
    double renderBinResolution;
    if (!getBinResolutions(v, binResolution, renderBinResolution)) return;

    for (int ix = 0; in_range_for(m_sources.peakCaches, ix); ++ix) {
        auto peakCache = ModelById::getAs<Dense3DModelPeakCache>
            (m_sources.peakCaches[ix]);
        if (!peakCache) continue;
        int bpp = peakCache->getColumnsPerPeak();
        ZoomLevel equivZoom(ZoomLevel::FramesPerPixel,
                            round(renderBinResolution * bpp));
#ifdef DEBUG_COLOUR_PLOT_CACHE_SELECTION
        SVDEBUG << "render " << m_sources.source
                << ": getPreferredPeakCache: zoomLevel = " << zoomLevel
                << ", cache " << ix << " has bpp = " << bpp
                << " for equivZoom = " << equivZoom << endl;
#endif
        if (zoomLevel >= equivZoom) {
            // this peak cache would work, though it might not be best
            if (bpp > binsPerPeak) {
                // ok, it's better than the best one we've found so far
                peakCacheIndex = ix;
                binsPerPeak = bpp;
            }
        }
    }

#ifdef DEBUG_COLOUR_PLOT_CACHE_SELECTION
    SVDEBUG << "render " << m_sources.source
            << ": getPreferredPeakCache: zoomLevel = " << zoomLevel
            << ", renderBinResolution " << renderBinResolution
            << ", peakCaches " << m_sources.peakCaches.size()
            << ": preferring peakCacheIndex " << peakCacheIndex
            << " for binsPerPeak " << binsPerPeak
            << endl;
#endif
}

void
Colour3DPlotRenderer::renderToCachePixelResolution(const LayerGeometryProvider *v,
                                                   int x0, int repaintWidth,
                                                   bool rightToLeft,
                                                   bool timeConstrained)
{
    Profiler profiler("Colour3DPlotRenderer::renderToCachePixelResolution");
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": [PIXEL] renderToCachePixelResolution" << endl;
#endif
    
    // Draw to the draw buffer, and then copy from there. The draw
    // buffer is at the same resolution as the target in the cache, so
    // no extra scaling needed.

    auto model = ModelById::getAs<DenseThreeDimensionalModel>(m_sources.source);
    if (!model) return;

    int h = v->getPaintHeight();

    clearDrawBuffer(repaintWidth, h);

    vector<int> binforx(repaintWidth);
    vector<double> binfory(h);
    
    int binResolution;
    double renderBinResolution;
    if (!getBinResolutions(v, binResolution, renderBinResolution)) return;

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "renderToCachePixelResolution: binResolution = "
            << binResolution << ", renderBinResolution = "
            << renderBinResolution << endl;
#endif
    
    for (int x = 0; x < repaintWidth; ++x) {
        sv_frame_t f0 = v->getFrameForX(x0 + x);
        double s0 = double(f0 - model->getStartFrame()) / renderBinResolution;
        binforx[x] = int(s0 + 0.0001);
#ifdef DEBUG_COLOUR_PLOT_REPAINT
        SVDEBUG << "renderToCachePixelResolution: getFrameForX("
                << x0 << " + " << x << ") yields " << f0
                << " with model start frame " << model->getStartFrame()
                << " giving s0 = " << s0 << ", so binforx[" << x << "] == "
                << binforx[x] << endl;
#endif
    }

    int peakCacheIndex = -1;
    int binsPerPeak = -1;

    getPreferredPeakCache(v, peakCacheIndex, binsPerPeak);
    
    for (int y = 0; y < h; ++y) {
        binfory[y] = m_sources.verticalBinLayer->getBinForY(v, h - y - 1);
    }

    int attainedWidth;

    if (m_params.binDisplay == BinDisplay::PeakFrequencies) {
        attainedWidth = renderDrawBufferPeakFrequencies(v,
                                                        repaintWidth,
                                                        h,
                                                        binforx,
                                                        binfory,
                                                        rightToLeft,
                                                        timeConstrained);

    } else {
        attainedWidth = renderDrawBuffer(repaintWidth,
                                         h,
                                         binforx,
                                         binfory,
                                         peakCacheIndex,
                                         rightToLeft,
                                         timeConstrained);
    }

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "renderToCachePixelResolution: attainedWidth = "
            << attainedWidth << endl;
#endif
    
    if (attainedWidth == 0) return;

    // draw buffer is pixel resolution, no scaling factors or padding involved
    
    int paintedLeft = x0;
    if (rightToLeft) {
        paintedLeft += (repaintWidth - attainedWidth);
    }

    m_cache.drawImage(paintedLeft, attainedWidth,
                      m_drawBuffer,
                      paintedLeft - x0, attainedWidth);

    for (int i = 0; in_range_for(m_magRanges, i); ++i) {
        m_magCache.sampleColumn(i, m_magRanges.at(i));
    }
}

QImage
Colour3DPlotRenderer::scaleDrawBufferImage(QImage image,
                                           int targetWidth,
                                           int targetHeight) const
{
    int sourceWidth = image.width();
    int sourceHeight = image.height();

    // We can only do this if we're making the image larger --
    // otherwise peaks may be lost. So this should be called only when
    // rendering in DrawBufferBinResolution mode. Whenever the bin
    // size is smaller than the pixel size, in either x or y axis, we
    // should be using DrawBufferPixelResolution mode instead
    
    if (targetWidth < sourceWidth || targetHeight < sourceHeight) {
        SVCERR << "ERROR: Colour3DPlotRenderer::scaleDrawBufferImage: "
               << "targetWidth " << targetWidth
               << " < sourceWidth " << sourceWidth
               << " or targetHeight " << targetHeight
               << " < sourceHeight " << sourceHeight << endl;
        throw std::logic_error("Colour3DPlotRenderer::scaleDrawBufferImage: Can only use this function when making the image larger; should be rendering DrawBufferPixelResolution instead");
    }

    if (sourceWidth <= 0 || sourceHeight <= 0) {
        throw std::logic_error("Colour3DPlotRenderer::scaleDrawBufferImage: Source image is empty");
    }

    if (targetWidth <= 0 || targetHeight <= 0) {
        throw std::logic_error("Colour3DPlotRenderer::scaleDrawBufferImage: Target image is empty");
    }        

    // This function exists because of some unpredictable behaviour
    // from Qt when scaling images with FastTransformation mode. We
    // continue to use Qt's scaler for SmoothTransformation but let's
    // bring the non-interpolated version "in-house" so we know what
    // it's really doing.
    
    if (m_params.interpolate) {
        return image.scaled(targetWidth, targetHeight,
                            Qt::IgnoreAspectRatio,
                            Qt::SmoothTransformation);
    }
    
    // Same format as the target cache
    QImage target(targetWidth, targetHeight,
                  QImage::Format_ARGB32);

    for (int y = 0; y < targetHeight; ++y) {

        QRgb *targetLine = reinterpret_cast<QRgb *>
            (target.scanLine(y));
        
        int sy = int((uint64_t(y) * sourceHeight) / targetHeight);
        if (sy == sourceHeight) --sy;

        const QRgb *sourceLine = reinterpret_cast<const QRgb *>
            (image.constScanLine(sy));

        int psx = -1;
        QRgb colour = {};
        
        for (int x = 0; x < targetWidth; ++x) {

            int sx = int((uint64_t(x) * sourceWidth) / targetWidth);
            if (sx == sourceWidth) --sx;

            if (sx > psx) {
                colour = sourceLine[sx];
            }
            
            targetLine[x] = colour;
            psx = sx;
        }
    }

    return target;
}

void
Colour3DPlotRenderer::renderToCacheBinResolution(const LayerGeometryProvider *v,
                                                 int x0, int repaintWidth)
{
    Profiler profiler("Colour3DPlotRenderer::renderToCacheBinResolution");
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": [BIN] renderToCacheBinResolution" << endl;
#endif
    
    // Draw to the draw buffer, and then scale-copy from there. Draw
    // buffer is at bin resolution, i.e. buffer x == source column
    // number. We use toolkit smooth scaling for interpolation.

    auto model = ModelById::getAs<DenseThreeDimensionalModel>(m_sources.source);
    if (!model) return;

    // The draw buffer will contain a fragment at bin resolution. We
    // need to ensure that it starts and ends at points where a
    // time-bin boundary occurs at an exact pixel boundary, and with a
    // certain amount of overlap across existing pixels so that we can
    // scale and draw from it without smoothing errors at the edges.

    // If (getFrameForX(x) / increment) * increment ==
    // getFrameForX(x), then x is a time-bin boundary.  We want two
    // such boundaries at either side of the draw buffer -- one which
    // we draw up to, and one which we subsequently crop at.

    sv_frame_t leftBoundaryFrame = -1, leftCropFrame = -1;
    sv_frame_t rightBoundaryFrame = -1, rightCropFrame = -1;

    int binResolution;
    double renderBinResolution;
    if (!getBinResolutions(v, binResolution, renderBinResolution)) return;

    int drawBufferWidth;

    // These loops should eventually terminate provided that
    // getFrameForX always returns a multiple of the zoom level,
    // i.e. there is some x for which getFrameForX(x) == 0 and
    // subsequent return values are equally spaced

    int edgeBinResolution = int(round(renderBinResolution));
    
    for (int x = x0; ; --x) {
        sv_frame_t f = v->getFrameForX(x);
        if (sv_frame_t (f / edgeBinResolution) * edgeBinResolution == f) {
            if (leftCropFrame == -1) leftCropFrame = f;
            else if (x < x0 - 2) {
                leftBoundaryFrame = f;
                break;
            }
        }
    }
    
    for (int x = x0 + repaintWidth; ; ++x) {
        sv_frame_t f = v->getFrameForX(x);
        if (sv_frame_t (f / edgeBinResolution) * edgeBinResolution == f) {
            if (v->getXForFrame(f) < x0 + repaintWidth) {
                continue;
            }
            if (rightCropFrame == -1) rightCropFrame = f;
            else if (x > x0 + repaintWidth + 2) {
                rightBoundaryFrame = f;
                break;
            }
        }
    }

    drawBufferWidth = int
        ((rightBoundaryFrame - leftBoundaryFrame) / renderBinResolution);

//    SVCERR << "rightBoundaryFrame = " << rightBoundaryFrame << ", leftBoundaryFrame = " << leftBoundaryFrame << ", renderBinResolution = " << renderBinResolution << ", drawBufferWidth = " << drawBufferWidth << endl;
    
    int h = v->getPaintHeight();

    // For our purposes here, the draw buffer needs to be exactly our
    // target size (so we recreate always rather than just clear it)
    
    recreateDrawBuffer(drawBufferWidth, h);

    vector<int> binforx(drawBufferWidth);
    vector<double> binfory(h);
    
    for (int x = 0; x < drawBufferWidth; ++x) {
        binforx[x] = int(leftBoundaryFrame / renderBinResolution) + x;
    }

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": renderBinResolution " << renderBinResolution << endl;
    SVDEBUG << "zoomLevel = " << v->getRoundedZoomLevel()
            << ", drawBufferWidth = " << drawBufferWidth << endl;
#endif
    
    for (int y = 0; y < h; ++y) {
        binfory[y] = m_sources.verticalBinLayer->getBinForY(v, h - y - 1);
    }

    int fullResolutionCacheIndex = -1;

    // If there is a peak cache with divisor 1, use it in preference
    // to the original source - it's presumably quicker, otherwise our
    // caller wouldn't have provided it. If we don't find one,
    // fullResolutionCacheIndex will remain at -1 which indicates to
    // use the original source direct
    for (int ix = 0; in_range_for(m_sources.peakCaches, ix); ++ix) {
        auto peakCache = ModelById::getAs<Dense3DModelPeakCache>
            (m_sources.peakCaches[ix]);
        if (!peakCache) continue;
        int bpp = peakCache->getColumnsPerPeak();
        if (bpp == 1) {
            fullResolutionCacheIndex = ix;
            break;
        }
    }
    
    int attainedWidth = renderDrawBuffer(drawBufferWidth,
                                         h,
                                         binforx,
                                         binfory,
                                         fullResolutionCacheIndex,
                                         false,
                                         false);

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "renderToCacheBinResolution: attainedWidth = "
            << attainedWidth << endl;
#endif

    if (attainedWidth == 0) return;

    int scaledLeft = v->getXForFrame(leftBoundaryFrame);
    int scaledRight = v->getXForFrame(rightBoundaryFrame);

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": scaling draw buffer from width " << m_drawBuffer.width()
            << " to " << (scaledRight - scaledLeft)
            << " (nb drawBufferWidth = "
            << drawBufferWidth << ", attainedWidth = "
            << attainedWidth << ")" << endl;
#endif

    QImage scaled = scaleDrawBufferImage
        (m_drawBuffer, scaledRight - scaledLeft, h);
            
    int scaledLeftCrop = v->getXForFrame(leftCropFrame);
    int scaledRightCrop = v->getXForFrame(rightCropFrame);
    
    int targetLeft = scaledLeftCrop;
    if (targetLeft < 0) {
        targetLeft = 0;
    }
    
    int targetWidth = scaledRightCrop - targetLeft;
    if (targetLeft + targetWidth > m_cache.getSize().width()) {
        targetWidth = m_cache.getSize().width() - targetLeft;
    }
    
    int sourceLeft = targetLeft - scaledLeft;
    if (sourceLeft < 0) {
        sourceLeft = 0;
    }

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": leftBoundaryFrame = " << leftBoundaryFrame
            << ", leftCropFrame = " << leftCropFrame
            << ", scaledLeft = " << scaledLeft
            << ", scaledLeftCrop = " << scaledLeftCrop
            << endl;
    SVDEBUG << "render " << m_sources.source
            << ": rightBoundaryFrame = " << rightBoundaryFrame
            << ", rightCropFrame = " << rightCropFrame
            << ", scaledRight = " << scaledRight
            << ", scaledRightCrop = " << scaledRightCrop
            << endl;
#endif
    
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": x0 = " << x0
            << ", repaintWidth = " << repaintWidth
            << ", targetLeft = " << targetLeft 
            << ", targetWidth = " << targetWidth << endl;
#endif
    
    if (targetWidth > 0) {
        // we are copying from an image that has already been scaled,
        // hence using the same width in both geometries
        m_cache.drawImage(targetLeft, targetWidth,
                          scaled,
                          sourceLeft, targetWidth);
    }
    
    for (int i = 0; i < targetWidth; ++i) {
        // but the mag range vector has not been scaled
        int sourceIx = int((double(i + sourceLeft) / scaled.width())
                           * int(m_magRanges.size()));
        if (in_range_for(m_magRanges, sourceIx)) {
            m_magCache.sampleColumn(i, m_magRanges.at(sourceIx));
        }
    }
}

int
Colour3DPlotRenderer::renderDrawBuffer(int w, int h,
                                       const vector<int> &binforx,
                                       const vector<double> &binfory,
                                       int peakCacheIndex,
                                       bool rightToLeft,
                                       bool timeConstrained)
{
    // Callers must have checked that the appropriate subset of
    // Sources data members are set for the supplied flags (e.g. that
    // peakCache corresponding to peakCacheIndex exists)

    Profiler profiler("Colour3DPlotRenderer::renderDrawBuffer");
    
    int divisor = 1;

    std::shared_ptr<DenseThreeDimensionalModel> sourceModel;

    if (peakCacheIndex >= 0) {
        auto peakCache = ModelById::getAs<Dense3DModelPeakCache>
            (m_sources.peakCaches[peakCacheIndex]);
        if (peakCache) {
            divisor = peakCache->getColumnsPerPeak();
            sourceModel = peakCache;
        }
    }

    if (!sourceModel) {
        sourceModel = ModelById::getAs<DenseThreeDimensionalModel>
            (m_sources.source);
    }
    
    if (!sourceModel) return 0;

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": renderDrawBuffer: w = " << w << ", h = " << h
            << ", peakCacheIndex = " << peakCacheIndex << " (divisor = "
            << divisor << "), rightToLeft = " << rightToLeft
            << ", timeConstrained = " << timeConstrained << endl;
    SVDEBUG << "render " << m_sources.source
            << ": renderDrawBuffer: normalization = " << int(m_params.normalization)
            << ", binDisplay = " << int(m_params.binDisplay)
            << ", frequencyMapping = " << int(m_params.frequencyMapping)
            << ", opaque = " << m_params.opaque
            << ", interpolate = " << m_params.interpolate << endl;
    SVDEBUG << "render " << m_sources.source
            << ": using sourceModel of type " << sourceModel->getTypeName()
            << endl;
#endif
    
    int sh = sourceModel->getHeight();
    
    int minbin = int(binfory[0] + 0.0001);
    if (minbin >= sh) minbin = sh - 1;
    if (minbin < 0) minbin = 0;

    int nbins  = int(binfory[h-1] + 0.0001) - minbin + 1;
    if (minbin + nbins > sh) nbins = sh - minbin;

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": minbin = " << minbin << ", nbins = " << nbins
            << ", last binfory = " << binfory[h-1]
            << " (rounds to " << int(binfory[h-1])
            << ") (model height " << sh << ")" << endl;
#endif
    
    int psx = -1;

    int start = 0;
    int finish = w;
    int step = 1;

    if (rightToLeft) {
        start = w-1;
        finish = -1;
        step = -1;
    }

    int xPixelCount = 0;
    
    int modelWidth = sourceModel->getWidth();

    QRgb *target = reinterpret_cast<QRgb *>(m_drawBuffer.bits());
    int targetWidth = m_drawBuffer.width();
    
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": modelWidth " << modelWidth << ", divisor " << divisor << endl;
    SVDEBUG << "render " << m_sources.source
            << ": start = " << start << ", finish = " << finish << ", step = " << step << endl;
#endif

    ColumnOp::Column preparedColumn;
    ColumnOp::Column aggregateColumn(nbins, 0.f);
    ColumnOp::Column distributedColumn(h, 0.f);
    
    RenderTimer timer(timeConstrained ?
                      RenderTimer::FastRender :
                      RenderTimer::NoTimeout);

    for (int x = start; x != finish; x += step) {

//        Profiler profiler("Colour3DPlotRenderer::renderDrawBuffer: per-pixel stuff");
    
        // x is the on-canvas pixel coord; sx (later) will be the
        // source column index
        
        ++xPixelCount;
        
        if (binforx[x] < 0) {
#ifdef DEBUG_COLOUR_PLOT_REPAINT
            SVDEBUG << "binforx[" << x << "] == " << binforx[x] << ", skipping"
                    << endl;
#endif
            continue;
        }

        int sx0 = binforx[x] / divisor;
        int sx1 = sx0;
        if (x+1 < w) sx1 = binforx[x+1] / divisor;
        if (sx0 < 0) sx0 = sx1 - 1;
        if (sx0 < 0) continue;
        if (sx1 <= sx0) sx1 = sx0 + 1;

#ifdef DEBUG_COLOUR_PLOT_REPAINT
        SVDEBUG << "x = " << x << ", binforx[x] = " << binforx[x] << ", sx range " << sx0 << " -> " << sx1 << endl;
#endif

        MagnitudeRange &magRange = m_magRanges.at(x);
        bool haveAnything = false;
        
        for (int sx = sx0; sx < sx1; ++sx) {

            // sx is the source column index, and we are stepping
            // through the source columns that contribute to current
            // on-canvas pixel x

            if (sx < 0 || sx >= modelWidth) {
                continue;
            }

            if (sx != psx) { // psx is index of existing preparedColumn, or -1
                
                // order:
                // get column -> scale -> normalise -> record extents ->
                // peak pick -> distribute/interpolate -> apply display gain

                // this does the first three:
                preparedColumn = getColumn(sx, minbin, nbins, false, sourceModel);

                magRange.sample(preparedColumn);

#ifdef DEBUG_COLOUR_PLOT_REPAINT
                SVDEBUG << "at sx = " << sx << ", sampled column giving mag range now = " << magRange.getMin() << " -> " << magRange.getMax() << endl;
#endif
                
                if (m_params.binDisplay == BinDisplay::PeakBins) {
                    preparedColumn = ColumnOp::peakPick(preparedColumn);
                }

                // (Display gain belongs to the colour scale and is
                // applied by the colour scale object when mapping it)
                
                psx = sx;
            }

            if (sx == sx0) { // first source column for this pixel
                haveAnything = true;
                aggregateColumn = preparedColumn;

            } else { // second or subsequent source column for this pixel
                for (int i = 0; i < nbins; ++i) {
                    aggregateColumn[i] = std::max(aggregateColumn[i],
                                                  preparedColumn[i]);
                }
            }
        }

        if (!haveAnything) {
            for (int y = 0; y < h; ++y) {
                target[y * targetWidth + x] = m_colourmap.at(0);
            }
        } else {

            ColumnOp::distribute(distributedColumn,
                                 aggregateColumn,
                                 h,
                                 binfory,
                                 minbin,
                                 m_params.interpolate);

            if (m_params.invertVertical) {
                for (int y = 0; y < h; ++y) {
                    auto value = distributedColumn[y];
                    auto pixel = m_params.colourScale.getPixel(value);
                    target[y * targetWidth + x] = m_colourmap.at(pixel);
                }
            } else {
                for (int y = h-1; y >= 0; --y) {
                    auto value = distributedColumn[y];
                    auto pixel = m_params.colourScale.getPixel(value);
                    int py = h - y - 1;
                    target[py * targetWidth + x] = m_colourmap.at(pixel);
                }
            }
        }            
                
        if (timeConstrained && (xPixelCount % 16 == 0)) {
            double fractionComplete = double(xPixelCount) / double(w);
            if (timer.outOfTime(fractionComplete)) {
#ifdef DEBUG_COLOUR_PLOT_REPAINT
                SVCERR << "render " << m_sources.source
                       << ": out of time with xPixelCount = " << xPixelCount
                       << ", fractionComplete = " << fractionComplete << endl;
#endif
                updateTimings(timer, xPixelCount);
                return xPixelCount;
            }
        }
    }

    updateTimings(timer, xPixelCount);

#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": completed with xPixelCount = " << xPixelCount << endl;
#endif
    return xPixelCount;
}

int
Colour3DPlotRenderer::renderDrawBufferPeakFrequencies(const LayerGeometryProvider *v,
                                                      int w, int h,
                                                      const vector<int> &binforx,
                                                      const vector<double> &binfory,
                                                      bool rightToLeft,
                                                      bool timeConstrained)
{
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": [PEAK] renderDrawBufferPeakFrequencies" << endl;
#endif

    // Callers must have checked that the appropriate subset of
    // Sources data members are set for the supplied flags (e.g. that
    // fft model exists)
    
    RenderTimer timer(timeConstrained ?
                      RenderTimer::SlowRender :
                      RenderTimer::NoTimeout);

    Profiler profiler("Colour3DPlotRenderer::renderDrawBufferPeakFrequencies");
    
    auto fft = ModelById::getAs<FFTModel>(m_sources.fft);
    if (!fft) return 0;

    int sh = fft->getHeight();
    
    int minbin = int(binfory[0] + 0.0001);
    if (minbin >= sh) minbin = sh - 1;
    if (minbin < 0) minbin = 0;

    int nbins  = int(binfory[h-1]) - minbin + 1;
    if (minbin + nbins > sh) nbins = sh - minbin;

    FFTModel::Peaks peakfreqs;

    int psx = -1;
    
    int start = 0;
    int finish = w;
    int step = 1;

    if (rightToLeft) {
        start = w-1;
        finish = -1;
        step = -1;
    }
    
    int xPixelCount = 0;
    
    ColumnOp::Column preparedColumn;

    int modelWidth = fft->getWidth();
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": modelWidth " << modelWidth << endl;
#endif
    
    double minFreq =
        (double(minbin) * fft->getSampleRate()) / fft->getFFTSize();
    double maxFreq =
        (double(minbin + nbins - 1) * fft->getSampleRate()) / fft->getFFTSize();

    QRgb *target = reinterpret_cast<QRgb *>(m_drawBuffer.bits());
    int targetWidth = m_drawBuffer.width();
    
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVDEBUG << "render " << m_sources.source
            << ": start = " << start << ", finish = " << finish
            << ", step = " << step << endl;
#endif
    
    for (int x = start; x != finish; x += step) {
        
        // x is the on-canvas pixel coord; sx (later) will be the
        // source column index
        
        ++xPixelCount;
        
        if (binforx[x] < 0) continue;

        int sx0 = binforx[x];
        int sx1 = sx0;
        if (x+1 < w) sx1 = binforx[x+1];
        if (sx0 < 0) sx0 = sx1 - 1;
        if (sx0 < 0) continue;
        if (sx1 <= sx0) sx1 = sx0 + 1;

        ColumnOp::Column pixelPeakColumn;
        MagnitudeRange &magRange = m_magRanges.at(x);
        
        for (int sx = sx0; sx < sx1; ++sx) {

            // sx is the source column index, and we are stepping
            // through the source columns that contribute to current
            // on-canvas pixel x

            if (sx < 0 || sx >= modelWidth) {
                continue;
            }

            if (sx != psx) { // psx is index of existing preparedColumn, or -1

                // The model should use its cache (as normal) if we
                // are retrieving a column that will subsequently be
                // used for peak calculations
                bool shouldCache = (sx == sx0 || sx == sx0+1 || sx+1 == sx1);
                bool suppressCache = !shouldCache;
                
                preparedColumn = getColumn(sx, minbin, nbins, suppressCache, fft);
                magRange.sample(preparedColumn);
                psx = sx;
            }

            if (sx == sx0) {
                pixelPeakColumn = preparedColumn;
                peakfreqs = fft->getPeakFrequencies(FFTModel::AllPeaks, sx,
                                                    minbin, minbin + nbins - 1);
            } else {
                for (int i = 0; in_range_for(pixelPeakColumn, i); ++i) {
                    pixelPeakColumn[i] = std::max(pixelPeakColumn[i],
                                                  preparedColumn[i]);
                }
            }
        }

        if (!pixelPeakColumn.empty()) {

#ifdef DEBUG_COLOUR_PLOT_REPAINT
//            SVDEBUG << "found " << peakfreqs.size() << " peak freqs at column "
//                    << sx0 << endl;
#endif

            for (FFTModel::Peaks::const_iterator pi = peakfreqs.begin();
                 pi != peakfreqs.end(); ++pi) {

                int bin = pi->first;
                double freq = pi->second;

                if (bin < minbin) continue;
                if (bin >= minbin + nbins) break;
            
                double value = pixelPeakColumn[bin - minbin];
            
                double y = v->getYForFrequency
                    (freq, minFreq, maxFreq, m_params.frequencyMapping);
            
                int iy = int(y + 0.5);
                if (iy < 0 || iy >= h) continue;

                auto pixel = m_params.colourScale.getPixel(value);

#ifdef DEBUG_COLOUR_PLOT_REPAINT
//                SVDEBUG << "frequency " << freq << " for bin " << bin
//                        << " -> y = " << y << ", iy = " << iy << ", value = "
//                        << value << ", pixel " << pixel << "\n";
#endif

                target[iy * targetWidth + x] = m_colourmap.at(pixel);
            }

        } else {
#ifdef DEBUG_COLOUR_PLOT_REPAINT
            SVDEBUG << "render " << m_sources.source
                    << ": pixel peak column for range " << sx0 << " to " << sx1
                    << " is empty" << endl;
#endif
        }

        if (timeConstrained && x < (w*2)/3 && (xPixelCount % 16 == 0)) {
            double fractionComplete = double(xPixelCount) / double(w);
            if (timer.outOfTime(fractionComplete)) {
#ifdef DEBUG_COLOUR_PLOT_REPAINT
                SVCERR << "render " << m_sources.source
                       << ": out of time with fractionComplete = "
                       << fractionComplete << endl;
#endif
                updateTimings(timer, xPixelCount);
                return xPixelCount;
            }
        }
    }

    updateTimings(timer, xPixelCount);
    return xPixelCount;
}

void
Colour3DPlotRenderer::updateTimings(const RenderTimer &timer, int xPixelCount)
{
    double secondsPerXPixel = timer.secondsPerItem(xPixelCount);

    // valid if we have enough data points, or if the overall time is
    // massively slow anyway (as we definitely need to warn about that)
    bool valid = (xPixelCount > 20 || secondsPerXPixel > 0.01);

    if (valid) {
        m_secondsPerXPixel = secondsPerXPixel;
        m_secondsPerXPixelValid = true;
    
#ifdef DEBUG_COLOUR_PLOT_REPAINT
    SVCERR << "render " << m_sources.source
           << ": across " << xPixelCount
           << " x-pixels, seconds per x-pixel = "
           << m_secondsPerXPixel << " (total = "
           << (xPixelCount * m_secondsPerXPixel) << ")" << endl;
#endif
    }
}

void
Colour3DPlotRenderer::recreateDrawBuffer(int w, int h)
{
    if (m_drawBuffer.width() != w || m_drawBuffer.height() != h) {
        m_drawBuffer = QImage(w, h, QImage::Format_ARGB32);
    }
    m_drawBuffer.fill(Qt::transparent);
    m_magRanges = vector<MagnitudeRange>(w);
}

void
Colour3DPlotRenderer::clearDrawBuffer(int w, int h)
{
    if (m_drawBuffer.width() < w || m_drawBuffer.height() != h) {
        recreateDrawBuffer(w, h);
    } else {
        m_drawBuffer.fill(Qt::transparent);
        m_magRanges = vector<MagnitudeRange>(w);
    }
}

QRect
Colour3DPlotRenderer::findSimilarRegionExtents(QPoint p) const
{
    QImage image = m_cache.getImage();
    ImageRegionFinder finder;
    QRect rect = finder.findRegionExtents(&image, p);
    return rect;
}
} // end namespace sv