On 11-Mar-2015 07:42, Tavmjong Bah wrote:

I also plan an expandable menu that allows setting the 'viewBox' directly as well as handling the case (hopefully rare) where the X scale and Y scale differ.

I suspect that X:Y set in the viewbox to anything other than 1:1 will not stay that way in a round trip through any other graphic format. Maybe one that has an exactly equivalent viewbox concept, if there is such a format. What is probably going to happen is that the corresponding transform will be applied and the new coordinates written to the other format (which has X:Y == 1:1), and when read back into Inkscape the new viewbox will still have X:Y scale be 1:1 but the size of the viewbox will have been scaled to compensate. "Probably" because I have never tested this scenario. It is also fairly likely that many of the other file formats will just screw up that export, since they may well assume a 1:1 viewport scale. So please, when you do implement this, test exports to other formats and note those that have problems.

Regards,

David Mathog mathog@...1176... Manager, Sequence Analysis Facility, Biology Division, Caltech

Hi, I just tried out rev 14031, which has the ability to use the Document Properties Dialog to modify the size of the viewbox. This appears to be working well, thank you very much! As I understand it, what this allows you to do is modify the viewbox definition independently of either the page size definition or the coordinates of the individual objects in the drawing. This will likely be of interest to non-Inkscape users who wish to use an svg drawing elsewhere, like in a web page. However, there is a second possible use of the viewbox that still needs to be addressed. This is the ability to simulate a change in the drawing coordinate system units without changing the visual appearance of the drawing. To do this, you need to leave the page size definition unchanged, and simultaneously scale both the viewbox definition and all of the coordinates of all the objects in the drawing by the same amount. This will allow you to switch the apparent document units from px, for example, to mm without changing the appearance. The reason this works is because the apparent size of an object is given qualitatively by the expression: (apparent size) = (page size)*(object size)/(viewbox size) where it is understood that the (object size) and (viewbox size) are expressed in the same physical units, so the ratio is a dimensionless number. This interpretation, namely the attempt to attach physical significance to the units of the individual objects and also the units of the viewbox, is outside the SVG spec, meaning it is not addressed by the spec, but it is not incompatible with it. Currently Inkscape supports a restricted form of the concept of document units, which would apply to both the individual objects and the viewbox. If you use the default_mm.svg file to start Inkscape, then you will get a drawing in which all the object coordinates, as well as the viewbox, appear to be expressed in mm. And if you use the file default_px.svg, then you will get a file that uses only px for all coordinates, as well as the viewbox. It is quite likely that one or the other of these formats will be highly preferable to some users. However, you cannot currently switch between these two formats, so if you accidentally used the wrong file at the start, you are stuck with it forever. The code for performing a live switch between these different formats is in the routine SPGroup::scaleChildItemsRec which has been temporarily disabled in rev 13748. I would like to advocate for, and propose, that this code be re-enabled as soon as possible, so that we can properly evaluate it. It provides a powerful tool that we can use to re-format documents to suit different users needs or preferences. It is true that there are a lot of bug reports associated with this change: http://wiki.inkscape.org/wiki/index.php/Units_In_Inkscape:_Document_Unit_Cha... however, it is also true that most of these bug reports referred to pre-existing structural problems which had simply been accidentally exposed by these document unit changes, and most of these reports have now been addessed or solved in one way or another, so it is time to re-evaluate the situation with a fresh pair of eyes.

Alvin

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