Allow user to specify screen resolution other than 90 dpi

Hi,

on debian's BTS I got the following report at
http://bugs.debian.org/326051 by Cyril Humbert (cyril
dot humbert at univ-mlv dot fr) some time ago:

"The zoom scale doesn't take into account the actual screen
resolution.

For example, with a 17" CRT monitor, if the screen size is
1024x768 (=> about 80 dpi):

- Open a new A4 document;
- Set the zoom factor to 100%;
- The page appears bigger than the A4 format (in fact, it
seems that a 90 dpi resolution is assumed).

Perhaps, it would be nice to have an option to manually
adjust which value is the screen resolution (like in e.g.
gimp or scribus)."

Thanks,

Wolfi

As far as I know most other SVG renderers also use fixed
resolution for px/absolute conversions. So long as they do,
I don't really think we need to fix this bug either. After
all SVG is not well suited for absolute units at all, the
spec recommends to always use px to avoid incompatibilities.

I guess I'm throwing in my vote to have this fixed as well.

It would be nice if 100% actually meant "this is what it
will look like printed", as opposed to, you know, "haha,
sucka!".

On my computer, everything is much too small at 100%. 15"
LCD at 1400x1050, at, iirc, 167dpi.

bug 168834 is a dupe of this one, with an emphasis on the rulers being incorrect.

There's a fundamental question. What to do if in the same document there are physical units (mm) and screen units (px)? Change document look if DPI has changed or stay as it is?

Two size types (actual screen size, screen*200%, screen*300% and actual physical size, physical*200%, physical*300%) is a poor solution. Maybe, the best solution remaining is to make such a thing.

In IS settings: Screen DPI (just for "physical scale") [ 96 ], and checkbox "Take DPI from system".
In zoom menu make two mutually-exclusive options: "Physical scale (depends on screen DPI)" and "Screen scale (1px=1/90in)"

DON'T SIMPLY TAKE SCREEN DPI FROM SYSTEM, let the user override it - the users tend to set the DPI depending on UI font rendering (at least in Windows), and "system inch" isn't necessarily an inch.

Actually, Mercury, SVG 'px' are treated everywhere in inkscape as physical units (at 1/90", just like a pt is 1/72"), so the mixture of SVG px and mm is not a problem.

Your proposed solution I think makes lots of sense. If the user is designing icons or web pages, and wants 1 SVG px == 1 screen pixel, then they use the default setting of 90dpi. If instead they are doing print work and want 1 SVG px == 1/90" (and therefore 1 document mm to equal 1 mm on screen) then they can set the value to their actual screen dpi.

I think the only think inkscape would have to change is the way the zoom factor is calculated...

What's up with this feature? I'm using inkscape 0.46 and the zoom is still wrong. I cannot see any of the new DPI settings anywhere in the menus.

It's quite simple. The CSS spec mentions a reference pixel of 90 DPI. There were a lot of internals hardcoded with such ratios. In order to allow for display-dependent zoom to occur, two main things need to happen.

First we need reliable cross-platform code to get accurate DPI info from displays. (This is not always a trivial matter)

Second, we need to change any code left with hardcodings. This is not quite trivial, but does need someone to step up and volunteer to do the work.

Well... if the code would have been C/no garbage collector... I would have done it. But, that's my choice. Hope you'll find somebody or time to do it.

I don't know if this is affected by this specific bug, but I'd like to be able to import raster images at 300DPI, if I import them now, they are >3x the size they should be in inches, and if I scale them to 90DPI, then export the vector file at 300DPI, the images will be much lower resolution than anything else.

Let me vote for that bug, as I think inkscape should not implicitly make a relative unit an absolute one. A default is very okay, let's say 90dpi or anything else. But the SVG-standard also emphasizes the "px" unit as "user unit", therefore relative and negotiable.

So by allowing absolute units (cm, in, em, pt...), SVG is indeed capable of designing "fixed"-sized elements, where sizes and zooms have to be interpretede by different software. mixing absolute/relative units may cause bad things to your SVGs when displaying them with different soft- and hardware.

Inkscape 0.47 introduced the "Zoom correction factor" setting in Inkscape Preferences->Interface. Is this a good enough solution?

As I said in my last comment, there is now a "zoom correction factor" setting available, which I believe satisfies the feature request. I'll leave this report open to gather opinions on this

I am using Inkscape 0.48+devel r (May 17 2013). The "zoom correction factor" allows to change the zoom factor. The zomm tool 1:1 makes the dimensions of the page to be shown correct. At the same time the information at the bottom right corner states that the zoom level is not 100%. I should be able to set zoom 1:1 just typing 100% in the box at the bottom right corner as well.