Method updateMapImage

qcustomplot/qcustomplot.cpp:25964–26039

! \internal Updates the internal map image buffer by going through the internal \ref QCPColorMapData and turning the data values into color pixels with \ref QCPColorGradient::colorize. This method is called by \ref QCPColorMap::draw if either the data has been modified or the map image has been invalidated for a different reason (e.g. a change of the data range with \ref setDataRan

  setInterpolate is true.
*/
void QCPColorMap::updateMapImage()
{
  QCPAxis *keyAxis = mKeyAxis.data();
  if (!keyAxis) return;
  if (mMapData->isEmpty()) return;
  
  const QImage::Format format = QImage::Format_ARGB32_Premultiplied;
  const int keySize = mMapData->keySize();
  const int valueSize = mMapData->valueSize();
  int keyOversamplingFactor = mInterpolate ? 1 : (int)(1.0+100.0/(double)keySize); // make mMapImage have at least size 100, factor becomes 1 if size > 200 or interpolation is on
  int valueOversamplingFactor = mInterpolate ? 1 : (int)(1.0+100.0/(double)valueSize); // make mMapImage have at least size 100, factor becomes 1 if size > 200 or interpolation is on
  
  // resize mMapImage to correct dimensions including possible oversampling factors, according to key/value axes orientation:
  if (keyAxis->orientation() == Qt::Horizontal && (mMapImage.width() != keySize*keyOversamplingFactor || mMapImage.height() != valueSize*valueOversamplingFactor))
    mMapImage = QImage(QSize(keySize*keyOversamplingFactor, valueSize*valueOversamplingFactor), format);
  else if (keyAxis->orientation() == Qt::Vertical && (mMapImage.width() != valueSize*valueOversamplingFactor || mMapImage.height() != keySize*keyOversamplingFactor))
    mMapImage = QImage(QSize(valueSize*valueOversamplingFactor, keySize*keyOversamplingFactor), format);
  
  if (mMapImage.isNull())
  {
    qDebug() << Q_FUNC_INFO << "Couldn't create map image (possibly too large for memory)";
    mMapImage = QImage(QSize(10, 10), format);
    mMapImage.fill(Qt::black);
  } else
  {
    QImage *localMapImage = &mMapImage; // this is the image on which the colorization operates. Either the final mMapImage, or if we need oversampling, mUndersampledMapImage
    if (keyOversamplingFactor > 1 || valueOversamplingFactor > 1)
    {
      // resize undersampled map image to actual key/value cell sizes:
      if (keyAxis->orientation() == Qt::Horizontal && (mUndersampledMapImage.width() != keySize || mUndersampledMapImage.height() != valueSize))
        mUndersampledMapImage = QImage(QSize(keySize, valueSize), format);
      else if (keyAxis->orientation() == Qt::Vertical && (mUndersampledMapImage.width() != valueSize || mUndersampledMapImage.height() != keySize))
        mUndersampledMapImage = QImage(QSize(valueSize, keySize), format);
      localMapImage = &mUndersampledMapImage; // make the colorization run on the undersampled image
    } else if (!mUndersampledMapImage.isNull())
      mUndersampledMapImage = QImage(); // don't need oversampling mechanism anymore (map size has changed) but mUndersampledMapImage still has nonzero size, free it
    
    const double *rawData = mMapData->mData;
    const unsigned char *rawAlpha = mMapData->mAlpha;
    if (keyAxis->orientation() == Qt::Horizontal)
    {
      const int lineCount = valueSize;
      const int rowCount = keySize;
      for (int line=0; line<lineCount; ++line)
      {
        QRgb* pixels = reinterpret_cast<QRgb*>(localMapImage->scanLine(lineCount-1-line)); // invert scanline index because QImage counts scanlines from top, but our vertical index counts from bottom (mathematical coordinate system)
        if (rawAlpha)
          mGradient.colorize(rawData+line*rowCount, rawAlpha+line*rowCount, mDataRange, pixels, rowCount, 1, mDataScaleType==QCPAxis::stLogarithmic);
        else
          mGradient.colorize(rawData+line*rowCount, mDataRange, pixels, rowCount, 1, mDataScaleType==QCPAxis::stLogarithmic);
      }
    } else // keyAxis->orientation() == Qt::Vertical
    {
      const int lineCount = keySize;
      const int rowCount = valueSize;
      for (int line=0; line<lineCount; ++line)
      {
        QRgb* pixels = reinterpret_cast<QRgb*>(localMapImage->scanLine(lineCount-1-line)); // invert scanline index because QImage counts scanlines from top, but our vertical index counts from bottom (mathematical coordinate system)