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Re: SVG Filter Regions confusion

From: Dirk Schulze <dschulze@adobe.com>
Date: Wed, 23 May 2012 11:06:05 -0700
To: Stephen Chenney <schenney@chromium.org>
CC: "www-svg@w3.org" <www-svg@w3.org>
Message-ID: <A7E9E608-DAE2-4583-AC98-4B11A1E554D2@adobe.com>
Hi Stephen,

On May 23, 2012, at 7:58 AM, Stephen Chenney wrote:

> The SVG 1.1 spec section 15.7.3 says this:
> 
> --------
> All intermediate offscreens are defined to not exceed the intersection of ‘x’, ‘y’, ‘width’ and ‘height’ with the filter region. The filter region and any of the ‘x’, ‘y’, ‘width’ and ‘height’ subregions are to be set up such that all offscreens are made big enough to accommodate any pixels which even partly intersect with either the filter region.
> --------
> 
> The first sentence explicitly defines the offscreen buffer size to be the intersection of the filter region and the filter effect subregions. The second sentence implies to me that the offscreen buffer size must be the union of the filter region and the filter effect subregions. I'm totally confused.
> 
> Is this just a case of bad phrasing? In particular, the phrase "are made big enough" could be "are big enough"  Is the intention to restrict the valid values of the subregions such that they remain inside the filter region?
> 
> Otherwise, what does it mean?

You can define the attributes 'x', 'y', 'width' and 'height' for every filter effect. If you do that, then these values indicate your clipping region. If one of the values is not defined, the clipping region on the missing dimension depends on the union of previous filter effects.

For this pseudo example the effect region is the union of the two effects 1 and 2.

<feOffset result="1"/>
<feOffset result="2"/>
<feComposite in="1" in2="2"/>

For this pseudo example, the effect is the region defined by the attributes 'x', 'y', 'width' and 'height'.

<feOffset result="1"/>
<feOffset result="2"/>
<feComposite in="1" in2="2" x="0" y="0" width="1" height="1"/>

The filter region depends on the union of the input effects for the dimension attributes that are missing.


Greetings,
Dirk

> 
> Stephen.
Received on Wednesday, 23 May 2012 18:08:04 GMT

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