[Kmymoney-devel] DPI Setting

[Jack]

On 2014.11.06 07:22, Allan wrote:
> I'm working on  [Bug 340656] New: The csv importer dialog display is  
> broken on high DPI screens.
> 
> Originally, on my system, I had not specified a specific setting for  
> DPI, and I was using the default, which I think was 96.  The OP  
> reported "This happens on a high DPI screen for which I had to force  
> the fonts DPI to 168.", and I am not at the moment clear if he  
> intended/needed to use that setting, or actually had to resort to  
> that.  I found there was certainly a problem at 168, so I'm assuming  
> that that was the setting he wanted to use.
> 
> I've now have it working at this setting, but if I go above that then  
> problems return, and font sizes need to be reduced.  In some places,  
> this responds to the new font size setting, but in some cases the  
> original size remains and recompilation is needed.
> 
> So, what setting is reasonable for me to use?  The higher settings  
> look like it might be good for making posters.
> 
> Allan

As has been said before, you should not need to (and generally should  
not) specify such things.  The issue with fonts is that there are often  
subtle misconfiguration of display systems.  A monitor has a real size  
(inches or mm), a real number of pixels, and a DPI.  You really only  
get to specify two, and from those calculate the third.  Since the  
first two are physical attributes of the monitor, they (in theory at  
least) should take priority.  However, for various reasons, DPI is  
sometimes specified, potentially leading to conflicts - i.e., it's  
sometimes not true that size of display in inches X DPI = number of  
pixels.

The problem with fonts is that you can specify them in pixels or by  
physical size (72 points = 1 inch, an old printers measure).  Only if  
all three of the above parameters are actually correct will this work.   
In addition, specifying either size or pixels for a font will simply be  
wrong on some display.  10 point type may be too large on a phone or  
small tablet, and will probably be too small on a 35 inch display.   
Likewise if you specify pixels.  You really have to assume the user has  
the display configured correctly, and that the default font size will  
be appropriate.  You can then specify "smaller" or "larger," but both  
are relative to the default font, not to any fixed baseline.

Unless you query this display parameters, I believe any attempt to  
specify font sizes will be wrong for some set of users.  By specifying  
a font family (serif v. sans, roman v. italic, bold v. plain, narrow v.  
normal or wide) you can get a particular look, and might even get a  
good idea of the aspect ratio of what you are displaying, but beyond  
that lies trouble.

For the specific user you refer to, it doesn't really tell us anything  
that he needed 168 DPI.  It depends on his monitor size and resolution,  
and whether they were set correctly.  Adjusting DPI is simply a  
post-hoc way of getting a useful output when something was specified in  
a way that was not appropriate for that display.  Setting your own  
display to 168 DPI doesn't really change the display, it just changes  
the calculations used to draw the fonts - and that depends on whether  
the underlying font being displayed is actually specified by pixels  
(any bit-mapped font) or in inches/points (true-type fonts, for  
example, if I remember correctly.)

I apologize if this sounds like a rant, but as displays have gotten  
both large and small, and unless you actually have a way of knowing  
about the display you are currently running on, and using that  
information, font size is likely to remain a problem.  Projection  
devices are yet another twist, since pixels are fixed but actual size  
depends on distance from the projector to the screen, and sizes can't  
be thought of in the usual way, since the people viewing the display  
are at a distance - so a true 10point type would be miniscule.

I suspect this is also at least peripherally related to the system  
choosing which size icon to use, and why most icons are created and  
installed in a range of sizes.  In general, you do not specify which  
size icon to use on a particular screen or dialog, but let the system  
choose the appropriate size.  I wonder if we will ever get icons  
specified by rendering (e.g., svg) rather than bitmapped.  If so, the  
issues become more parallel to fonts.

Jack