Inkscape

On Thu, 2003-12-11 at 13:06, Lauris Kaplinski wrote:
> SVG spec is resolution agnostic.

Yes, but I finally read this part of the SVG spec...

> All its units are just
> defined as certain ratios of undefined base unit (pixel), that
> may or may not be related to some real-world unit.

For the initial coordinate system, the SVG specification refers to
CSS2's definition of length units, which broadly specifies two classes
of units:

 1. relative units which do NOT have fixed relationships with real-world
units

   * em and ex: determined by the current font size
   * px: determined by the user agent, generally some multiple of device
pixels

 2. absolute units which _are real-world units_ (subject to the
user-agent's ability and desire to match them)

   * mm: real-world mm
   * cm: 10 mm
   * in: 2.54 cm
   * pt: 1/72 in
   * pc: 12 pt

> Sodipodi document has real-world dimensions.
> To map resolution agnostic SVG onto real-world paper, it uses
> mapping:

> 1 SVG point =3D=3D 1 typographic point

(To be totally pedantic, typographic points are 0.0138 in, which is not
_quite_ the same as Postscript/SVG points [1/72 =3D 0.01388888...]; I
think everyone uses the Postscript definition nowadays though.)

> As 1SVG point =3D=3D 1.25 SVG pixels, and pixels are SVG base units,
> SVG base unit =3D=3D 0.8 typographic points on all sodipodi documents.

Unless a viewBox is set, the relationship between user-space base units
(pixels) and the absolute units is totally user-agent dependent.

(this is why all examples in the SVG spec specify a viewBox)

Thinking about this, if Sodipodi intends to be completely interoperable,
it needs to always write a default viewBox according to the base
units/points mapping it imposes.

e.g. for a document 100ptx100pt, the viewBox should be "0 0 125 125".

-mental

[Inkscape-devel] Re: [Sodipodi-list] Re: 0.8 multiplier From: MenTaLguY <mental@ry...> - 2003-12-19 04:47 Attachments: Message as HTML      On Sat, 2003-12-13 at 05:10, Lauris Kaplinski wrote: > > (this is why all examples in the SVG spec specify a viewBox) > >=20 > > Thinking about this, if Sodipodi intends to be completely interoperable= , > > it needs to always write a default viewBox according to the base > > units/points mapping it imposes. > >=20 > > e.g. for a document 100ptx100pt, the viewBox should be "0 0 125 125". >=20 > Are you saying, that 'width' and 'height' attributes of outermost > SVG have different semantics, as the same attributes in inner elements? > AFAIK it is not the case, so viewBoxonly changes the meaning of: > A) Percentages (as these are not defined as % of viewbox) > B) Base units by ratio of width/viewBox_width and height/viewBox_height > - but as width and height are in relative units, this is no > different that applying 'transform'. Consider these two SVG documents (I'll leave out namespace/XML declarations and other boilerplate for brevity): <svg width=3D"100pt" height=3D"100pt"> <rect x=3D"12.5" y=3D"12.5" width=3D"100" height=3D"100" fill=3D"black" stroke=3D"none"/> <rect x=3D"10pt" y=3D"10pt" width=3D"80pt" height=3D"80pt" fill=3D"none" stroke=3D"red" stroke-width=3D"1pt"/> </svg> and: <svg width=3D"100pt" height=3D"100pt" viewBox=3D"0 0 125 125"> <rect x=3D"12.5" y=3D"12.5" width=3D"100" height=3D"100" fill=3D"black" stroke=3D"none"/> <rect x=3D"10pt" y=3D"10pt" width=3D"80pt" height=3D"80pt" fill=3D"none" stroke=3D"red" stroke-width=3D"1pt"/> </svg> Well, hrm. Having just tried this with Batik, I think it reveals a fundamental misunderstanding I had about viewBox. So, for the document root it appears that the relationship between pixel and non-pixel measurements can never be guaranteed to be fixed between different UAs/display devices. Doesn't this mean that Sodipodi should probably be using pixel measurements, not real-world units, for the height/width properties of the root SVG element? (and probably using e.g. sodipodi:height and sodipodi:width, or possibly sodipodi:dpi to derive the real-world measurements the UI uses?) Otherwise, in other SVG UAs, the relationship between the drawing and page size is not guaranteed to be the same. -mental

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