I have made a small test program, by hand, with no LCL and no RAD
utilities. It is boring and a lot of dirty work, but not difficult (If I
could do it, it can't be difficult, my programming skills are rusted
after years of programming sales reports). I have taken a look at QT
widget, and perhaps it shouldn't be that difficult integrating web with LCL.
I've made myself such web widget set, which have the same API as LCL.
Thus its simple to recompile desktop application to gain web application
its huge (>1000 forms) program which is use by hundreds user day by day .
I've mention about it a few times, i work with it from years, and I
think that HTML5 + Pascal is the best tool to web application.
Nevertheless I have found issues that have little to do with RAD, they
are related to the concept of remote GUI itself.
Let's suppose you have a checkbox that when cheked must enable some
controls. In a common desktop the event is sent to the application, and
application process the event and tells the GUI which controls must
enable. But if the application is remote, the roundtrip may take 30 ms,
add a cascade of events triggered and you get that you uncheking a
chekbox the application gets stalled for a moment or more (I read
somewhere that to get the "no time" perception it must react in less
than 100ms). I said 30ms but it could be 200ms depending on the
connection, and then the moment may become a second.
No time perception is under 300ms.
No one controls must wait to response from server to change its look,
this do JS lying under each. But of course, each user action is
transmitted to server and respond carry information of look other
controls. In other words: each control take care only of itself, no
business logic is include in JS, rest is done by server.
The solution to this problem is quite easy, and it is what many web-GUI
interfaces do: Move part of program to the client side, so they send big
javascripts to the client. No objection, I don't think it's a big deal
to send javascript libraries to the client, as long as it is transparent
for me as developer. What I intend to avoid, when I write an
application, is having to write half application in pascal and half
application using javascript. I want to write the whole application in
pascal and let the libraries use javascript or whatever they want.
This is outlined, as I do: 95% in pascal and 5 in JS+CSS+HTML
Probably I'm demanding too much, there is no way a component can say "I
will convert this few lines of code into a javascript and send it to the
client"
I dont send JS for controls, only some HTML like (real copy)
<td colspan="2" xcol="19"><div id="dfaF5FB9B20" class=" fieldhint
fieldliczba"><input id="faF5FB9B20" type="text" onchange="return
chk('aF5C5E030','faF5FB9B20');" value=""></div></td>
rest is done by JS + CSS
by the way: CSS id great, allows for separation of look and behavior,
its far better than LCL
Beside this, there are concerns with http protocol, it is document
oriented, not connection oriented. For example, unless you keep the
connection open, every event from GUI to application, even a single
byte, must send a lot header information, let alone if you use cookies
that are sent with every connection. There are workarounds, comet, html5
websockets, perhaps with some drawbacks.
This is not problem. Today network is fast, sending packet information
under size of frame (<1400bytes) has no overhead.
Pooling : only 1 request for 15 s, its under 0.001% overhead.
Much difficult is architecture of HTTP server. I need modal windows,
thus I use 3 levels of thread. If add logging, timers or background task
then levels count. But its work the same as on desktop (only nicer)
Darek
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