My understanding is that the origin cited in the specification is the origin of
current image, not the origin of a parent or source image. Otherwise given that
RenderedImage.getSources() can return an arbitrary amount of source (or parent)
images, which one would define the origin?
But anyway, while I agree that the first part of the sentence has ambiguity because of
different possible interpretations of "origin", the second part of the sentence
is much clearer:
i.e., the X coordinate of the upper-left pixel of tile (0, 0). (Note that
tile (0, 0) may not actually exist.)
Note that this part does not exists in the specification of the BufferedImage.
So we can write:
tileGridXOffset = minX - minTileX * tileWidth
(Note: Java Advanced Imaging was also doing this mathematics if my memory
serves me right.)
In BufferedImage implementation, getMinTileX() and getNumTileX() are hard-coded
to 0 and 1 respectively, while getMinX() and getTileWidth() delegate to raster
methods. If we substitute variables in above formulas by BufferedImage
implementations we get:
tileGridXOffset = raster.getMinX() - 0 * raster.getTileWidth()
which simplify as:
tileGridXOffset = raster.getMinX()
Where raster.getMinX() always returns 0 in BufferedImage case, consistently
with BufferedImage javadoc which said getTileGridXOffset() value is always zero.
I agree that all calculation above are valid for the simple BufferedImage, but
not sure about sub image, will check the history of the file and its usage.
--
Best regards, Sergey.
