Re: drops module (draft)

[Peter Rolf <indiego@gmx.net>]

Am 06.12.2012 19:05, schrieb Aditya Mahajan:
> On Thu, 6 Dec 2012, Peter Rolf wrote:
> 
>> Hi all,
>>
>> a first version of the 'drops'-module (MkIV only) is available at
>>
>> https://www.wuala.com/indiego/public/ConTeXt/drops/?key=caiCGLasLFmJ
>>
>>
>> Taken from the included documentation..
>> [..]
>> 'drops' is a small extension for ConTeXt, that allows you to add drop
>> shadows to rectangular regions (so called boxshadows). A working
>> installation of ImageMagick (IM) is required to create the shadow
>> graphics. The supported color spaces are CMYK, RGB and Gray, the file
>> formats are limited to PNG and JPG.
>> [..]
>> Read the manual for detailed information.
> 
> Nice.
> 
>> The attached example is just a small test file for the 'rotation'
>> parameter (a compensation for the object rotation, so that the shadow
>> stays at the given direction). You will find other examples in the
>> documentation and there is also a 'pile' example with the complete
>> source. The 'presets' pdf contains the predefined setups for different
>> shadow (or frame) types and it's source is a good starting point for
>> your own experiments.
>>
>> This is a first draft, but most things work quite stable. If you want to
>> help, test as much as possible. :-)
>>
>> *You need a recent version of ImageMagick for this module.*
> 
> I always thought that shadows were possible to do in PDF (after all TikZ
> does it using some type of PDF primitives). Since you are the PDF
> expert, I am interested in knowing why you choose to go the ImageMagic
> route.
>
Because it's relative simple (I use a working function) , fast (in terms
of rendering speed) and the footprint of the shadow graphics is not that
big (png: one color, only alpha channel differs). Quality is (as you can
see) also not an issue. Mh, there is nothing wrong with bitmaps ;-)

See Type4/Type5 Shadings (Free-Form Gouraud-Shaded Triangle Meshes) on
page 314 of the PDF Reference for the PDF alternative. The problems to
solve are the calculation of the mesh points (think about rounded
squares) and also to find a proper shading function (which sets the
colors). See 'Shadow Internals' at

http://www.imagemagick.org/Usage/blur/#shadow%20internals

Far from trivial (and I'm only an amateur with limited time).

Also: you can 'draw' (command of IM) any shape in IM (SVG paths are
supported) and use the 'shadow' function on that. Theoretically you can
extent drops to support any shape (path or drawing). That's one reason
why I used the more general name 'drops' instead of the currently better
fitting 'boxshadow'. The other reason is, that Hans would never use the
stupid name 'drops' internally. :-D

> In terms of interface, wouldn't it be better if this somehow interfaced
> with the background/overlay mechanism. For example,
> 
> \definedropshadow[identifier][...options...]
> 
> which will define an overlay that will call ImageMagic with appropriate
> parameters (and caching the results if speed is a concern),
> 
> and then
> 
> \externalfigure[name][background=identifier]
> 
> should draw a dropped shadow around the image
> 

Needs some thinking


> Aditya
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