A better way to handle texture scale/cache

[RadarNyan]

IMO, getting every subrectangle and hash them separately is totally overkill.

Since the "random" data could only shows up at the end of texture (in ram), if it's possible to get the last line being used before, just hash from the beginning to this line will be totally solve the problem isn't it?

   
Is it possible to get the last pixel of the drawing area?
Actually it's not necessary to get last pixel, just the last line will be enough. Then we just keep update the last line (of the same texture, of course) if a new drawing area's last line is bigger than current value, at last we will end up with a line that actually been used from this texture.
(well, this texture doesn't need this method at all... Just grabbed a random one)

And if we can manage to get this "correct range", is it possible to only scale this range of texture? Because those "random" data is really really slowing down the texture scale process.

But the problem is, how can we get this unique id of a texture? A same address could be totally used by different textures right?