displayRectToSourceRect function

Rect displayRectToSourceRect({ required Rect cropRect, required Rect imageDisplayRect, required Size sourceSize, })

Convert a crop rect from display coordinates to source-image pixel coordinates.

The display rect (cropRect) and the image's current display rect (imageDisplayRect) share the same coordinate space (whatever Stage uses — typically the screen). The source image lives in its own pixel space (sourceSize). This function maps the crop rect into that pixel space via the scale ratio between the displayed image and its source.

Implementation

Rect displayRectToSourceRect({
  required Rect cropRect,
  required Rect imageDisplayRect,
  required Size sourceSize,
}) {
  if (imageDisplayRect.width == 0 || imageDisplayRect.height == 0) {
    return Rect.zero;
  }
  final scaleX = sourceSize.width / imageDisplayRect.width;
  final scaleY = sourceSize.height / imageDisplayRect.height;
  return Rect.fromLTWH(
    (cropRect.left - imageDisplayRect.left) * scaleX,
    (cropRect.top - imageDisplayRect.top) * scaleY,
    cropRect.width * scaleX,
    cropRect.height * scaleY,
  );
}