createImage method

Image createImage(int width, int height)

Generate a ARGB image based on normalized gradient. The width and height of the image are specified as input parameters. The output is a Flutter Image widget.

Implementation

Image createImage(int width, int height) {
  // prepare bitmap structure
  GuiBitmapBuffer gbmp = GuiBitmapBuffer(
      width: width,
      height: height,
      bitsPerPixel: GuiBitmapBuffer.bitsPerPixelArgb);
  Uint8List data = gbmp.imageData;
  int offset = 0;

  // check if width and height are valid
  if (width < 1) width = 1;
  if (height < 1) height = 1;

  // set start of stop idx to stop 0.0
  int curStopIdx = mapStop0Idx;
  // get begin gradient
  double begYStop = mapStops[curStopIdx];
  List<GuiGradientColor> begGrad = colormap[begYStop]!;
  // get end gradient
  curStopIdx++;
  double endYStop = mapStops[curStopIdx];
  List<GuiGradientColor> endGrad = colormap[endYStop]!;

  double yStopIncrement = (height > 1) ? (1.0 / (height - 1)) : 1.0;
  double xStopIncrement = (width > 1) ? (1.0 / (width - 1)) : 1.0;

  // For each row
  double yStop = 0;
  for (int y = 0; y < height; y++, yStop += yStopIncrement) {
    // get offset for row
    offset = gbmp.imageRowOffset(y);
    // get gradient stop
    while (yStop > endYStop) {
      begYStop = endYStop;
      begGrad = endGrad;
      curStopIdx++;
      if (curStopIdx >= mapStops.length) break;
      endYStop = mapStops[curStopIdx];
      endGrad = colormap[endYStop]!;
    }
    List<GuiGradientColor> curGrad =
        GuiNormalizeGradient.getGradientInBetween(
            yStop, begGrad, begYStop, endGrad, endYStop);

    // get color range
    int curGgcIdx = gradientStop0Idx;
    GuiGradientColor begGgc = curGrad[curGgcIdx];
    curGgcIdx++;
    GuiGradientColor endGgc = curGrad[curGgcIdx];
    double xStop = 0.0;
    for (int x = 0; x < width; x++, xStop += xStopIncrement) {
      while (xStop > endGgc.stop) {
        begGgc = endGgc;
        curGgcIdx++;
        if (curGgcIdx >= curGrad.length) break;
        endGgc = curGrad[curGgcIdx];
      }
      // get color for offset at (x,y)
      Color clr =
          GuiNormalizeGradient.getColorInBetween(xStop, begGgc, endGgc);
      // PixelFormat.rgba8888
      data[offset] = clr.blue;
      data[offset + 1] = clr.green;
      data[offset + 2] = clr.red;
      data[offset + 3] = clr.alpha;
      // increment offset
      offset += gbmp.bytesPerPixel;
    }
  }
  // convert data into image
  return gbmp.toImage();
}