Calling lqt apps as an extension to another program

[Saptarshi Joy Guha]

Hello,

Not the best subject, so let me explain. I am demonstrating the ease of use of using luajit and terra as an extension language to R.
One example will include using lqt for displays

E.g. inside R

doTerraFile("myfile.t")
doTerra("doTest",1)

doTest is a lua function

contents of myfile.t:

require 'qtcore'
require 'qtgui'
function doTest(x)
   local app = QApplication.new(2, {'lua','-nograb'})
   local w = QWidget.new()
   function w:closeEvent(e)
      print('Closing!')
   end
   w:show()
   app.exec()
   print("HELLEOE")
   return nil
end

This works quite nicely. However, app.exec grabs the event loop and only returns upon close. Fair enough.

However, since I am embedding inside R, it would be nice to be able to return control to R and allow the app to run alongside.

Would such a thing enable it? E.g. a
app = nil
function makeEmbedApp(x)
  app = QApplication.new(#x, x)
    Call-to-C++ function-called-RunInT(app)

RunInT creates a subclass of QThread, and repeatedly calls processevents on app.

Thus the presumable the above code would still work and the control would be returned to R.
However, this implies lqt contain that bit of C++ code (though I could write my own, other users of lqt wouldn't have it unless it comes with lqt)

Is this sensible or just plain wrong?
Cheers
Saptarshi

[Michal Kottman]

I looked at this, and it seems it is possible to run your own version of the event loop. [1] You just have to write the event loop yourself.

[1] http://stackoverflow.com/questions/1051333/combing-an-external-event-loop-with-qts

After some experimentation, this is what I came up with:

require 'qtcore'

require 'qtgui'

local App = QApplication(1, {"Test"})

local Btn = QPushButton("Quit!")

local running = true

Btn:show()

Btn:connect('2clicked()', function()

running = false

end)

while running do

QCoreApplication.processEvents() -- call this inside the event loop

end

I am not sure how it will behave in Terra, but feel free to try it out.

[Saptarshi Guha]

Yes something similar. I followed the usual approach to integrating within R's eventloop.

The code looks like (note, I'm using Terra). qtinit is called first.

Thanks!

require 'qtcore'
require 'qtgui'
pthread = terralib.includec("pthread.h")
local ifd = global(int)
local ofd = global(int)
local fired=global(int,0)
local qtwriterthread = global(pthread.pthread_t)
local App = nil
local mu = {}
function processQTEvents(x)
   QCoreApplication.processEvents()
end
terra QTEventLoopHandler(data : &uint8)
   var buf : uint8[16]
   unistd.read(ifd,buf,16)
   processQTEvents()
   fired=0
end
terra mywriter(data : &uint8) : &uint8
   var buf : uint8[16];
   while true do
      unistd.usleep(10000)
      if fired == 0  then
     fired = 1
     buf[0]=0
     var s = unistd.write(ofd, buf, 1);
      end
   end
end
terra QTEventLoopInit()
   var fds : int[2]
   if unistd.pipe(fds) == 0  then
      ifd,ofd = fds[0],fds[1]
      Rinternals.addInputHandler(R.constants.InputHandlers,ifd,QTEventLoopHandler,31)
      Rinternals.setCStackLimit(-1)
      pthread.pthread_create(&qtwriterthread,nil,mywriter,nil);
   end
end
function qtinit(a)
   App = QApplication(1, {"qtbase", "-nograb"})
   QTEventLoopInit()
end

function doTest2(x)
   mu.Btn = QPushButton("Quit!")
   local running  = true
   mu.Btn:show()
   mu.Btn:connect('2clicked()',
          function()
             print("BYeeee\n")
             mu.Btn:close()
           end)
   return nil
end

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