Re: [css-masking] CR from 2014-08-26: 'Appendix B: Compute stroke bounding box'

Dirk Schulze:
> “Inflate a rectangle” is an often used expression in computer science and
> means that a rectangle is enlarged by a specified amount. The rectangle and
> the amount are defined in the spec.
>
> Greetings,
> Dirk
>

As already mentioned in the question about the draft, it is not obvious, how
to 'Inflate box with the value of delta.' 
In this email I already guessed some method, how to enlarge the rectangle,
but not sure, whether this is correct or that this results somehow in the 
intended box with some intuitive relation to the stroke of the shape (if this 
is really the task, not described at all in the CR for this feature).

The current prose can result in different implementations for such an 
inflation - those may contain additive operations or multiplicative or even
complex approximations or a mixture of all of this.
The result is not necessarily always related to what I assume is intended:
The smallest box aligned horizontally and vertically in the local coordinate
system, that contains a stroked object or group of stroked objects (not 
excluding objects without stroke).
Because there is no prose about such a purpose or functionality of a
stroke bounding box, it is not even obvious, that my assumption is 
correct or that others may have other assumptions about this,
especially due to the complexity of the problem to render combinations
of stroke properties, even if stroke dashing is explicitly excluded.

I still have a lot of fun examples with strange rendering results
for objects where the width of a stroke is bigger than the typical
diameter of the object - therefore I assume, that if there is no precise
prose or formula for this, here we can get soon some more test-fun 
and surprises with non trivial examples for paths.
'Inflate box with the value of delta.'  is in general not testable, at least
not with quantitative tests.

Olaf

Received on Thursday, 4 September 2014 13:59:56 UTC