GUI Messages

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On-screen GUI messages can be rendered in FlightGear using a simple property-based messaging system which is using property listeners and the PUI GUI system.

Note  Canvas event handlign conflicts with PUI event handling in the sense that it takes precedence - there never really was the intention to fix that, because all the people involved in the original discussion ended up agreeing that PUI should be retired ASAP, i.e. it would not be worth the hassle to make PUI<->Canvas event handling work more properly.[1]

it's really not a new thing, and is indeed explicitly mentioned in the Canvas docs - however, most people will be unaware of the back-end (like you say), i.e. the corresponding messages basically being transparent PUI dialogs (IIRC), so that the corresponding limitations apply, without people necessarily being aware of the culprit.



Cquote1.png The ATC subsystem shouldn't really generate the message *and* display it, no matter which method is used. It should rather only set a property to the generated message, for example /sim/messages/atc. A different subsystem should then take this message and display it -- using the same code for ATC and other screen messages. It should be glue code that decides what to do with the message property (c++ and Nasal listeners). Send it to the screen like now, print it to the console, forward it to the speech synthesis module
— Melchior FRANZ (Feb 4th, 2006). [Flightgear-devel] Re: screen.nas: log windows.
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Whatever is written to /sim/messages/* at runtime is shown on-screen for a few seconds, then moved away. When the next message is written to that node, that is moved on-screen. Behind the scenes, this works by using a property listener/callback that is triggered whenever the property tree branch is modified.


It would make sense to use the Canvas tooltip framework and adapt the screen.nas code accordingly: Tooltips[3]


This system is primarily used by the following features:

None of those are hard-coded, those are all going through the property tree and gui.nas, so you can "disable" things there. The higher-level features are limits.nas (or the failure manager) and the tutorial system.

The corresponding code can be found in gui.nas and screen.nas

To change the font size

Cquote1.png Set /sim/gui/style[1]/fonts/message-display/name
— Csaba Halász  (Nov 23rd, 2008). Re: [Flightgear-devel] screen.window size of font.
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Cquote1.png with TIMES_24
— gerard robin (Nov 23rd, 2008). Re: [Flightgear-devel] screen.window size of font.
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To disable the system completely, set /sim/screen/nomap=true to prevent default message mapping - e.g. as a startup option --prop:/sim/screen/nomap=1 and/or by editing $FG_HOME/Preferences.xml

In addition, there's the tooltip system which is meanwhile using the Canvas 2D rendering API

Related content

Wiki articles

Forum topics

Source code

  1. Hooray  (Jul 1st, 2016).  Re: canvas vs. on-screen messages - 1:0 .
  2. Hooray  (Jul 1st, 2016).  Re: canvas vs. on-screen messages - 1:0 .
  3. Hooray  (Jul 1st, 2016).  Re: canvas vs. on-screen messages - 1:0 .