void paintImage({@required Canvas canvas, @required Rect rect, @required Image image, ColorFilter colorFilter, ImageFit fit, ImageRepeat repeat: ImageRepeat.noRepeat, Rect centerSlice, FractionalOffset alignment })

Paints an image into the given rectangle in the canvas.

  • canvas: The canvas onto which the image will be painted.
  • rect: The region of the canvas into which the image will be painted. The image might not fill the entire rectangle (e.g., depending on the fit).
  • image: The image to paint onto the canvas.
  • colorFilter: If non-null, the color filter to apply when painting the image.
  • fit: How the image should be inscribed into rect. If null, the default behavior depends on centerSlice. If centerSlice is also null, the default behavior is ImageFit.scaleDown. If centerSlice is non-null, the default behavior is ImageFit.fill. See ImageFit for details.
  • repeat: If the image does not fill rect, whether and how the image should be repeated to fill rect. By default, the image is not repeated. See ImageRepeat for details.
  • centerSlice: The image is drawn in nine portions described by splitting the image by drawing two horizontal lines and two vertical lines, where centerSlice describes the rectangle formed by the four points where these four lines intersect each other. (This forms a 3-by-3 grid of regions, the center region being described by centerSlice.) The four regions in the corners are drawn, without scaling, in the four corners of the destination rectangle defined by applying fit. The remaining five regions are drawn by stretching them to fit such that they exactly cover the destination rectangle while maintaining their relative positions.
  • alignment: How the destination rectangle defined by applying fit is aligned within rect. For example, if fit is ImageFit.contain and alignment is FractionalOffset.bottomRight, the image will be as large as possible within rect and placed with its bottom right corner at the bottom right corner of rect.

Source 

void paintImage({
  @required Canvas canvas,
  @required Rect rect,
  @required ui.Image image,
  ColorFilter colorFilter,
  ImageFit fit,
  ImageRepeat repeat: ImageRepeat.noRepeat,
  Rect centerSlice,
  FractionalOffset alignment
}) {
  assert(canvas != null);
  assert(image != null);
  Size outputSize = rect.size;
  Size inputSize = new Size(image.width.toDouble(), image.height.toDouble());
  Offset sliceBorder;
  if (centerSlice != null) {
    sliceBorder = new Offset(
      centerSlice.left + inputSize.width - centerSlice.right,
      centerSlice.top + inputSize.height - centerSlice.bottom
    );
    outputSize -= sliceBorder;
    inputSize -= sliceBorder;
  }
  fit ??= centerSlice == null ? ImageFit.scaleDown : ImageFit.fill;
  assert(centerSlice == null || (fit != ImageFit.none && fit != ImageFit.cover));
  final FittedSizes fittedSizes = applyImageFit(fit, inputSize, outputSize);
  final Size sourceSize = fittedSizes.source;
  Size destinationSize = fittedSizes.destination;
  if (centerSlice != null) {
    outputSize += sliceBorder;
    destinationSize += sliceBorder;
    // We don't have the ability to draw a subset of the image at the same time
    // as we apply a nine-patch stretch.
    assert(sourceSize == inputSize);
  }
  if (repeat != ImageRepeat.noRepeat && destinationSize == outputSize) {
    // There's no need to repeat the image because we're exactly filling the
    // output rect with the image.
    repeat = ImageRepeat.noRepeat;
  }
  Paint paint = new Paint()..isAntiAlias = false;
  if (colorFilter != null)
    paint.colorFilter = colorFilter;
  if (sourceSize != destinationSize) {
    // Use the "low" quality setting to scale the image, which corresponds to
    // bilinear interpolation, rather than the default "none" which corresponds
    // to nearest-neighbor.
    paint.filterQuality = FilterQuality.low;
  }
  double dx = (outputSize.width - destinationSize.width) * (alignment?.dx ?? 0.5);
  double dy = (outputSize.height - destinationSize.height) * (alignment?.dy ?? 0.5);
  Point destinationPosition = rect.topLeft + new Offset(dx, dy);
  Rect destinationRect = destinationPosition & destinationSize;
  if (repeat != ImageRepeat.noRepeat) {
    canvas.save();
    canvas.clipRect(rect);
  }
  if (centerSlice == null) {
    final Rect sourceRect = (alignment ?? FractionalOffset.center).inscribe(
      fittedSizes.source, Point.origin & inputSize
    );
    for (Rect tileRect in _generateImageTileRects(rect, destinationRect, repeat))
      canvas.drawImageRect(image, sourceRect, tileRect, paint);
  } else {
    for (Rect tileRect in _generateImageTileRects(rect, destinationRect, repeat))
      canvas.drawImageNine(image, centerSlice, tileRect, paint);
  }
  if (repeat != ImageRepeat.noRepeat)
    canvas.restore();
}