On Wed, 25 Sep 2013 11:23:07 -0700 Bryce Harrington <bryce@...961...> wrote:
Really, there are (at least) three different ways the unit system touches the real world.
Thanks for this well-thought-out explanation; it clarifies the situation considerably.
I think a modified version of my "display scale factor" proposal can accommodate all the cases you describe; see attached image.
The improvement is to let the user explicitly specify the three ratios between screen/drawing/export units (although this obviously involves only two degrees of freedom). "Export" would mean PDF or similar, if the image was intended for paper, or PNG/JPG/GIF, if it was intended for electronic display.
The "zoom factor" setting would still be present; this would be multiplied with the "screen units" setting when displaying the document on a monitor, so that 100% zoom would produce the specified screen:drawing unit ratio. It would have no effect on the drawing:export unit ratio.
First is the physical measurements of the page. For instance, if you're going to fold a 8.5"x11" paper into forths and want a logo to appear in the middle of the cover, you're going to care about seeing position in document inches.
In this case, you would set the drawing:export ratio at 1:1 , so that the measurements would come out right in the PDF or PostScript file.
The screen:drawing ratio can be set to any value that is convenient for working on the document, without having any effect on the eventual paper image.
Second is the physical measurement of the monitor. If you're making assets for a website or buttons for a cell phone UI, you'll care about display pixels, display mm's, etc. and probably don't care about paper at all. It's possible you care about the dpi of some product display that you don't have access to (so don't just assume the attached monitor's dpi is the one the user cares about.)
Here again, you would set the drawing:export ratio at 1:1 , specified in either "px" or "mm", depending on how you wanted to measure the image.
The screen:drawing ratio could also be set at 1:1 , if this provided an appropriate view of the image, or some larger value, for detailed work on icons, etc.
Third is the physical measurement of the thing the drawing is conceiving. If you're drawing a map, then you'll care about km's and miles. You may care about how many printed page inches or cm's correspond to how many miles or km's.
In this case you would set the drawing:export ratio at 1km:3cm , or 5miles:2inches , or something like that.
If the screen:export ratio is set to 1:1 , the drawing should appear on the monitor at the same size as it eventually will on a paper map, or whatever the target output is.
Personally, this third use case is the one I care about, but when I was doing the original units system it became clear that the SVG spec cared mostly about the first one, and somewhat the second, and it wasn't at all clear how to handle the third.
It seems to me that <g transform="scale(x)"> nodes, possibly with Inkscape-specific attributes, could be used to control the relationship between document/image/display units, for the SVG tree, but this would require further thought.
Indeed, it seems there is even difficulty in trying to make it handle #1 and #2 in a user-intuitive way. At the least, it all made me very confused.
Leaving aside for the moment the question of how to do this in an SVG-compliant way, does my proposal above (and attached image) make sense to you? Does it adequately address the situations you've described, or any others that you can think of?
I wonder if perhaps what we should do here is ignore SVG's units and consider the three (or more) use cases that users have, and think from their POV what would work best.
I agree with that. Decide first what the Inkscape UI should be like, and how it should control exported image sizes, and figure out later how to map that onto standard (or proposed, as <tavmjong@...8...> says) SVG.
Establish different unit systems "modes" and let the user toggle which units mode to use in the Inkscape UI while drawing.
Does it really require "modes", or does allowing the user to explicitly control the screen/drawing/export unit ratios provide all the control that is actually needed?
-- Ian Bruce
