[plt-scheme] 2htdp/image & 2htdp/universe update

On Jan 6, 2010, at 12:15 AM, Robby Findler wrote:

> Recently, in SVN and in the nightly builds, 2htdp/universe changed to
> support both the original htdp/image library as well as the
> 2htdp/image library. Specifically:
> 
>  - 2htdp/universe no longer exports any image library; require both
> 2htdp/universe and either htdp/image or 2htdp/image


The image functionality in 2htdp/universe was transferred to htdp/image, so if you now require 

 2htdp/universe and htdp/image 

you get the old functionality back. 


>  - 2htdp/image now supports cropping; see place-image and
> place-image/align (as well as 'crop').
> 
>  - image equality is now defined in terms of drawing the images at
> their current sizes, specifically comparing the particular set of
> pixel values that get drawn by the two images to see if they are the
> same.
> 
> The change to the way image equality works simplifies the semantics of
> image comparison significantly (and, in the presence of cropping, I'm
> not even sure I want to try to figure out a structural equality), but
> at a runtime cost. Nevertheless, image comparison in 2htdp/image is
> still between 3x and 30x faster than equality on htdp/image images,
> depending on the complexity of the image (the more complex the image,
> the better 2htdp/image performs, relative to htdp/image).
> 
> Note that these changes are not set in stone yet. We welcome
> experimentation and feedback on them.
> 
> Robby
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