Re: [Plplot-devel] Driver behavior questions and wingdi preview

[Phil R. <p.d...@gm...>]

Yeah, that seems like a good argument to me

On 15 June 2015 at 03:30, Jim Dishaw <ji...@di...> wrote:
>
> On Jun 14, 2015, at 5:28 AM, Phil Rosenberg <p.d...@gm...> wrote:
>
> On 11 June 2015 at 17:57, Jim Dishaw <ji...@di...> wrote:
>
>
> On Jun 11, 2015, at 4:06 AM, Phil Rosenberg <p.d...@gm...> wrote:
>
> Hi Jim
> The documentation states that the provided text height will be in mm.
> The user can set dpi with plspage so you should use the PLStream->xdpi
> and PLStream->ydpi to size your text in pixels. In case the user
> hasn't set this you should use a sensible default. Of course the
> actual value will depend on the monitor, but rather than try to grab
> this it seems that there are two standards and for consistency you
> should use one of these. One is to use 72 pixels per inch so that 1
> pixel = 1 pt. The other is 90 pixels per inch which seems to be the
> default for most svg renderers. For wxWidgets I chose 90 pixels per
> inch. I also noticed tect seems a little smaller than the example
> online (from the cairo driver?) but it does as described in the
> documentation so I am happy with that.
>
>
>
>
>
> The recommendation in the Windows API is to use GetDeviceCaps () with the
>>LOGPIXELSX/LOGPIXELSY values to get the dpi setting.  Right now I’m
>>ignoring the DPI setting provided by the user.  On native text rendering
> devices >the xdpi/ydpi settings are essentially being used to scale the size
> of fonts, >which (IMHO) abuses the meaning of “DPI”.
>
> Yes as you say the windows API provides this mechanism - in fact there
> is something about if you wish to have your app in the windows store
> you must do this so your app can work on phones/tablets/pcs or
> something. Not sure of the details.
> For The windows interactive device it is perhaps not a big deal - for
> wxWidgets the user can pass in a paint dc or a memory dc so in the
> latter case it is down to the user to specify a DPI. Because all DCs
> are treated equal it is up to the user in all instances. Re DPI
> basically being a text scaling parameter - well you are correct - but
> does any other function receive arguments in mm/inches or is text the
> only one?
>
>
> At least when it comes to DPI, text is the only that uses that field.  I
> think all the drawing commands are in the plot coordinate system, thus
> physical dimensions are subsumed into the coordinate system.  There is
> plsvpa() that allows the user to specify the viewport in terms of physical
> measurements.
>
> My rationale for keeping the dpi tied to the device is to ensure that
> physical measurements are invariant (the principle of least surprise).  If
> the API says “mm” or “inches” the driver should render something that
> measures correctly.
>
> Which size are you referring to?  When the window is resized, the driver
> gets >the new dimensions of the client area (via GetClientRect() for
> displays and >GetDeviceCaps() for printers).  It uses the new size to
> calculate the new >scaling between device virtual coordinates
> (PIXELS_X/PIXELS_Y in PLplot) >and the new output device coordinates, The
> dpi remains consistent with what >Windows reports.
>
> So for wxWidgets if I resize the window to double the size, the text
> stays the same size. I.e. I maintain the same dpi and text height in
> mm when the window is resized.
>
>
> Same with wingdi.  When resized the text stays the same.
>