RFR: 8243255: Font size is large in JavaFX app with enabled Monocle on Raspberry Pi

[John Neffenger]

On Thu, 23 Apr 2020 23:58:19 GMT, John Neffenger <github.com+1413266+jgneff at openjdk.org> wrote:

>> I couldn't understand why I wasn't hitting this error on the embedded Monocle EPD platform. Stepping through the code
>> with the debugger, I found that JavaFX is looking for the *javafx.platform.properties* file in the wrong place. I moved
>> the file to its parent directory, the location JavaFX expects, and saw the problem right away.  The first image below
>> shows the button and text without the properties file, and the second image shows the problem once the properties file
>> is loaded:
>> ![normal](https://user-images.githubusercontent.com/1413266/80154159-e05ac600-8573-11ea-897b-49a82baaa10f.png)
>> ![toobig](https://user-images.githubusercontent.com/1413266/80154165-e3ee4d00-8573-11ea-8b67-45670b17b7f1.png)  So
>> there might be a secondary problem. After unzipping the SDK archive under *$HOME/lib*, the properties file is located
>> at the following location on my system:  /home/ubuntu/lib/armv6hf-sdk/lib/javafx.platform.properties
>> 
>> Yet
>> [`com.sun.javafx.PlatformUtil.loadProperties`](https://github.com/openjdk/jfx/blob/master/modules/javafx.base/src/main/java/com/sun/javafx/PlatformUtil.java#L248)
>> looks in the following three locations, in order:  /home/ubuntu/lib/armv6hf-sdk/javafx.platform.properties
>> /home/ubuntu/opt/jdk-14.0.1+7/lib/javafx.platform.properties
>> /javafx.platform.properties
>> 
>> The first is based on the "runtime directory," the second is based on the value of *java.home*, and the third is based
>> on the value of *javafx.runtime.path*, which is `null` on my system.
>> @AlexanderScherbatiy Did you move the *javafx.platform.properties* file to its parent directory manually, as I just did?
>
> Wow, this is going to take some getting used to. �� Below is a photograph of the button and text with two changes:
> 
> 1. the code from this pull request, and
> 2. the `javafx.platform.properties` file moved to its parent directory.
> 
> ![withfix](https://user-images.githubusercontent.com/1413266/80160191-d344d380-8581-11ea-8fd4-09023ad30610.jpg)
> 
> The native screen on this platform returns 167 for its DPI. In general, the devices I'm testing have pixel densities of
> either 167 or 300 pixels per inch.

I got out my trusty C-Thru Ruler (GA-96), and the type now measures 12 points, just as intended.

**PrismFontFactory.getSystemFontSize**
  } else if (isEmbedded) {
      try {
          int screenDPI = Screen.getMainScreen().getResolutionY();
          systemFontSize = ((float) screenDPI) / 6f; // 12 points
      } catch (NullPointerException npe) {
          // if no screen is defined
          systemFontSize = 13f; // same as desktop Linux
      }
  } else {
      systemFontSize = 13f; // Gnome uses 13.
  }

Without the platform properties file, I've been running (for years!) with a default font size of 13 pixels, which on
this device is very small: (13 px ÷ 167 px/in) × 72 points/in = 5.60 points.

Now JavaFX is setting `isEmbedded` to `true`, picking up the correct screen DPI, and I'm finally getting a good default
font size: ((167 px/in ÷ 6 per in) ÷ 167 px/in) × 72 points/in = 12.0 points. Amazing.

-------------

PR: https://git.openjdk.java.net/jfx/pull/193