I'm developing a C++ application which will run on a headless server and keep track of some statistics. The application will run in a terminal in a screen session so that I can login over SSH and check those statistics.
Now, what I want to do, is display plots of various data. For that I need pixel-per-pixel access of course, which is not possible with ncurses or S-Lang. I found out about DirectFB (and it's C++ wrappers DFB++ & ++DFB), but can't seem to find conclusive evidence if it is possible to draw graphics with it inside a terminal.
Is DirectFB the way to go? Will it work fine inside a screen session without creating extra windows? If not, is there any library out there that can achieve what I want?
Edit: Ideally, I would of course prefer a library that has some kind of widget support as well, so that I don't have to create tons of classes to emulate text fields/scrollbars/...
You could make your application have a web interface. You could use e.g. Wt or Onion to make your application an HTTP server (or you could make it a FastCgi application), and use SVG (perhaps with Javascript and Ajax tricks) to display vector graphics (or generate a pixel-based PNG or JPEG or GIF image; there are several libraries for that).
I don't think that DirectFB works with SSH, and I believe it is becoming deprecated (for example GTK3 don't support it anymore).
You might also generate Gnu Plot graphics (by generating the appropriate commands), but that is not very interactive.
I don't think that making graphics thru ssh without X make sense, unless you want only ASCII art (which I believe is not the right way for your needs).
Related
I am writing an application using Qt and want to try and deploy it as a web-application. I want user's to be able to use my application by accessing it through a web browser. I'm guessing that's what a web-application is? What kind of options do I have? I've never looked into doing anything like this but I'd like to learn something new.
EDIT: What if I deployed my application on a Linux server and had users access/run it through a terminal? I think writing web application is going to be more complicated than I had originally thought.
If all you have is a Qt application, then the best you can do is use Qt 5 and run it using a remote visualization package:
Use WebGL streaming, introduced in Qt 5.10. Qt exposes a browser-connectible interface directly, without need for third-party code.
For Qt 5.0-5.9, you can use the vnc platform plugin. Then connect using a web-browser based vnc client.
For many uses it might be sufficient, and certainly it's much less effort than coding up a web app.
You're looking for Wt which provides a different set of drawing routines for many Qt GUI elements, turning them from lines on screen to HTML controls.
http://www.webtoolkit.eu/wt
It also handles websocket calls to provide interactivity. It seems a great idea, let us know how it works in practice.
For the case of QML there is QmlWeb which is a JavaScript library that is able to parse QML-code and create a website out of it using normal HTML/DOM elements and absolute positions within CSS, translating the QML properties into CSS properties.
QmlWeb is a small project by Lauri Paimen that he’s already developing for a few years now. QmlWeb of course doesn’t yet support everything Qt’s implementation of QML does, but it already supports a quite usable subset of it. It supports nearly all of the most basic QML syntax. Moreover it has support for HTML input elements (Button, TextInput, TextArea are currently supported, more to come).
Well, QmlWeb is not finished. I hope Digia help with this project to make it ready with mature features.
Interestingly, it is possible to compile Qt applications to javascript using emscripten-qt. These run fairly fast with Firefox's asm.js interpreter:
http://vps2.etotheipiplusone.com:30176/redmine/projects/emscripten-qt/wiki
Try "Qt for Webassembly".
Webassembly allows the C/C++ code to be compiled and run natively inside majority of the browsers:
WebAssembly (Wasm, WA) is a web standard that defines a binary format and a corresponding assembly-like text format for executable code in Web pages. ... It is executed in a sandbox in the web browser after a verification step. Programs can be compiled from high-level languages into Wasm modules and loaded as libraries from within JavaScript applets ... Its initial aim is to support compilation from C and C++, though support for other source languages such as Rust and .NET languages is also emerging.
To run a Qt application unchanged over the web so users can operate it in a browser, you can compile it for Android using the x86 Android ABI, run it inside an Android emulator on a server and supply the Android Cast videostream to users' browsers. You'll also need to have JavaScript in place that records the keyboard and mouse events on the web clients and relays them back to the server.
I had previously tried Qt WebGL streaming and found it to be good over the local network but too slow over the Internet. A 10 s application startup time is acceptable, but 3 s to show a new screen is rather not. I had the exact same experience with the Qt VNC platform plugin. Compared with that, the Android Cast streaming based appetize.io solution (see below) was much faster, providing a well usable user experience even over my 8 Mbit/s connection.
Existing solutions
Here is an overview of commercial products and open source software components that I found that can help you with this approach:
appetize.io. This is a commercial product to run Android applications over the web for demo and testing purposes. I have just done this with a Qt QML based application and liked the outcome. When choosing an Android 9 / 10 device you can see that the "Screencast" setting is on; which is why I believe that this solution uses the Android Cast technology.
runthatapp.com. This is another commercial offer. Not as sophisticated (yet) as appetize.io, but providing a nice pay-as-you-go scheme.
ScreenStream. An open source Android app that provides a web server to view the screen of one Android device in a web browser, also relying on the Android Cast technology. That Android device could be an emulator running on a web server. And to make this multi-user capable you can employ a small load balancer similar to a technique that I developed for Qt WebGL streaming. The ScreenStream README shows that the application might consume up to 20 Mbit/s per client in short bursts.
Ideas for future improvements
Serving your Qt app as an interactive live video stream seems a promising idea to me, given that I found it already less sluggish than VNC and similar solutions. There are ways to make this even faster, such as using a hardware H.265 video encoder to create a video stream with very little delay. By operating multiple such encoders on a single server, the server could serve multiple clients and still keep its CPU load low. Maybe there are even better video formats for such a purpose, given that user interfaces of programs lend themselves well to lossless compression.
Some hints for appetize.io
Finally: since I used the appetize.io product for a Qt application over the last few days, here are some tips from that experience:
It is necessary to compile your Qt application for the x86 Android ABI. The default armeabi-v7a ABI will not work because most appetize.io devices are actually server-based Android emulators and the only ARM based device ("Nexus 5 Physical") failed to start any Qt application I tried to use with it.
The x86_64 ABI may also work, but you might then have to also compile Qt yourself for it, as not all versions of Qt come pre-compiled for that architecture.
All appetize.io links (both for standalone pages and embeddable iframes) support GET parameters to configure the app presentation format. Especially relevant here is screenOnly=true to show the app without a picture of a phone or tablet around it.
Features that rely on phone hardware (camera, position etc.) will not work or only show dummy data. But if you really wanted, you could create a hybrid application combined with client-side JavaScript. It would run device-dependent code in the user's browser, for example to take a photo with the webcam, and then provide the results to the Qt application via the appetize.io cross-document messaging protocol. The following message types seem suitable to build a simple communication protocol: pasteText(value), keypress(key, shiftKey) and openUrl(value).
In the default appetize.io standalone app demo pages, only the key events of ordinary letter keys are sent to the app, not keyboard shortcuts or function keys like F2 and Esc. This might be possible to fix with JavaScript on an own page embedding the appetize.io iframe, as their cross-document messaging protocol provides the keypress(key, shiftKey) message type.
Qt does not support writing browser based web applications. Unfortunately.
You need to use common web programming technologies for this. There are a lot of ways, but Qt is not one of them.
I am looking to get started with some 3D programming in C or C++. The problem I have is that it seems like the only tutorials I can find for Mac OS use objective C and Cocoa frameworks. I want to obtain the same environment as Windows users, more or less.
If I try to use a text editor and g++ compiler, I am missing headers, but, if I try to use Xcode, I am forced to grapple with Cocoa, which is frustrating to me. I don't really see any reason why the OpenGL/GLUT that comes pre-installed on Mac should force me to use Xcode, but it seems I can't get the header files without it.
How can I get through all of the Apple 'developer friendly' interfaces to write some old-fashioned code with full cross-platform portability?
Some portion of Objective-C is inevitable if you want to use the latest benefits of the OSX/Cocoa. The easiest way to port an existing application to MacOS would be the following:
Write the "bare bones" nibless application in Objective-C. It would only be a single AppDelegate class and a little setup in the main() function
Add the custom NSGLView descendant in your window which you create in the AppDelegate's didFinishLaunching event handler
Setup the CVDisplayLink and rendering callback in the NSGLView initialization
Use your existing OpenGL rendering code in the CVDisplayLink's callback
Now for the interesting part: where to get all of this ?
Surprisingly, a good nibless application sample is the UI for OSX's port of QEMU (yes, the emulator). Also the Apple's official GLEssenstialPractices demo shows all the information you need to set up OpenGL rendering pipeline. All the rest is up to you.
The detailed and modern introduction to system-level OSX programming can be found in the "Advanced Mac OS X Programming" book by Mark Dalrymple. It explains many things and after reading all of this I've understood most of the design decisions in the OS (it really makes you accept all the "non-standard" things if you think from the performance viewpoint).
To get through the "nibless" programming I would recommend you to read the blog posts like this one http://blog.kleymeyer.com/2008/05/creating-cocoa-applications-programatically-ie-nib-less/ The google search helps a lot.
The same tricks apply to the CocoaTouch/iOS and there are a lot of questions answered on SO, like this one Cocoa touch/Xcode - generating NIB-less graphics context
If you want to create cross-platform applications you could create a project with the Command Line Tool template.
Next, import the OpenGL and GLUT framework. This will get you a "blank" C++ project with the required OpenGL and GLUT headers.
Lighthouse 3D gives you some tips about portability and how to initiate your first project.
http://www.lighthouse3d.com/tutorials/glut-tutorial/initialization/
I have created a software layer (named cocoglut) that allows the translatation of basic or essential GLUT calls to COCOA. This library allows creating/destroying windows and register callbacks from a C/C++ application, just by using GLUT calls, without the need for nib files or for XCode project files (and can be compiled from the command line). This option uses full retina display resolution. The source is on GitHub.
I'm currently working on a cross-platform application (Win/OSX/iOS) which has a C++ (with Boost) back end. On iOS and OSX I'm using the Cocoa Net Service Browser Delegate functions to discover an embedded device via mDNS, then pass the information to the back end to create the objects it needs to communicate with it.
I wanted to take a similar approach with my Windows MFC front end and I found this article which seemed to do exactly what I want. However, it seems that using the Bonjour SDK has some really nasty side effects - forcing you to static link to MFC and in my case the only way I can get it to link properly is to not use debug DLLs at all, which is not ideal.
So, the Bonjour SDK isn't really any good for me because it imposes too many restrictions on my project. With Cocoa I'm actually using very little of the functionality - just didFindService and netServiceDidResolveAddress really. All I want to do is find the devices of a given type and get their IP addresses.
Can anyone suggest another way around this that will work with an MFC front end on Windows?
From what I have been able to gather from researching this topic just goto http://www.opensource.apple.com/source/mDNSResponder/mDNSResponder-333.10/ and grab the source. There is a VC project file which will let you build the dll how you want.
The scenario is such: there's a program which loads my .dll/.so and calls a function from within it, possibly multiple times, each time expecting a different pointer to state. It uses the different states later in other calls into the dll. (It's a game AI, if you need context; each state is a AI player.)
What I want is a cross-platform way of creating a canvas window for each of those states (for visualization, debugging, etc.) I tried wx, but put it on hold, since it didn't appear to be easy at all. Are there any neat and small libraries that could do that or should I just go with WinAPI/X...?
Edit: Assume I cannot modify the host program.
Qt is simpler to set up and drive than Wx, in my experience. It's very cross platform too.
If you want to render some graphics from inside your DLL function without passing in any pointers to QImage or QWidget type things, probably the thing to do is use OpenGL. Your DLL should just render to the current OpenGL context, which is global state and can just be setup outside the DLL (maybe using QGLWidget).
Update: Ah, I just noticed your edit re not being able to modify the host code. This is a problem: any windows you create really need to be plugged into the host apps' event loop to work properly (e.g receive WM_PAINT when exposed/resized). It's certainly possible in win32 for any old code (e.g your library) to just CreateWindow and draw its contents with GDI whenever it gets the chance, but the general window behaviour may be pretty broken (it may not work at all with Vista's double buffering; I haven't tried). What I typically find easiest in this situation is simply to dump out image files and review then afterwards with image viewer of choice. IMHO this is actually more useful for debugging than a "live" window because you can step backwards and forwards, zoom in, apply image-enhancement to highlight various issues, compare against previous runs for regression testing etc etc. (If you really want the "live" views, write an image displayer which monitors a directory for new images, or streams them through a named pipe or something).
If you just want simple graphics, no widgets, SDL is very easy to use. If you do need complex controls, use Qt, as timday said.
You might check out IUP. It interfaces really well with Lua, and can be used entirely from an extension DLL there so it seems plausible that its C API could be used from a DLL plugged into something else.
IUP will get you a framework for opening a window containing the usual suspect kinds of controls, including a canvas. Its related library CD will give you the usual drawing operations in that canvas.
Current releases are portable between Windows and *nix. The next major release will support MacOSX too.
This is NOT a question on plain old boring customization; I actually want to create an program, you know, with source code, etc...
I'm thinking about programming my own media centre interface, and I figured it'd look better if I coded my own splash screen for when the OS is loading.
Note: The media centre interface will be run in X, but this question is regarding what will happen before the X server loads.
Simply, I'd like to make a splash screen application to hide the linux kernel boot messages. Is there a way I can program some animation in to this like some sort of animated progress bar for example? I assume that I won't be able to code any 2D/3D graphics (as that'd require X to be running, right?), so how would I go about generating that?
I'd prefer to do this in C++, but C is also an option.
Note: I'm not looking to use any existing "themes" or anything like that, just interested in the programming side of things.
Update:
Some suggestions have been to use standard images (.bmp, .jpeg, etc), I am not interested in loading images in to an existing application. But obviously I may want to load images in to the boot screen application that I will make.
I'm not tied to a Linux distro, so this can be for anything, although Debian or a Debian-based distro would be nice.
I like the suggestion about loading the X server early and running a loading screen from there, however is there not a more direct approach? Surely you can make a program which hides the boot messages and shows a custom program? Obviously this would be very low level programming, but that's what I'm looking for...
Also, I'm not interested in altering the boot loader (LILO, GRUB, etc).
Update 2:
So far good suggestions have been looking at the source code for applications like splashy and fbsplash. Can anyone better this suggestion?
For the graphical output you can use the Linux framebuffer, for application development you can use gtk which support rendering directly to the framebuffer GtkFB.
For the video and such you can use mplayer which also support rendering to the framebuffer.
For the initialization you have to look around the system used, debian uses a sysv init style initialization http://www.debian-administration.org/articles/212, ubuntu uses upstart.
I'd look into splashy source code. But you will need to code in C.
If you have the skills, you can implement a software based 3D engine (like in the good old days). A simple rotating cube shouldn't be very hard to code and there are tons of tutorials.
The downside is that you will increase the boot time, something not very pleasant in a media center.
Here's the thing: there is a library/kernel patch, fbsplash, that has already been written to do exactly what it sounds like you want to do. It will display an image in place of the normal boot messages, and it can also incorporate a progress bar. When you're trying to do something for which a well-established open-source implementation already exists, there's really no better way to learn how to do it yourself than to look at the source code.
Even if you're looking for something more complicated (say if you want to create some fancier animation than a progress bar), you might be able to start with fbsplash and modify it to suit your needs.
There are several ways you could do this. You could have the X server load very early, and just write a program to display the splash screen. You could also use the framebuffer device. If you are using Intel hardware, or are willing to use the OSS AMD drivers, or Nouveau for Nvidia, you could use kernel mode setting. For this, I would look at Fedora's Plymouth. You could just write a Plymouth plugin to display your splash screen.
The splash screen is simply an image (.bmp, .jpg, etc.) and can be loaded by the boot loader. Since you haven't specified the distribution you're using, look into LILO, grub, or whichever one is appropriate. Check the /boot directory for clues that will direct your search.
If all you want to do is have a nice clean boot sequence with your own splash and absolutely no boot messaging you can do the following:
First, silence grub, boot messaging, and console cursor:
GRUB_CMDLINE_LINUX_DEFAULT = quiet fastboot splash vt.cur_default=1 loglevel=0
GRUB_TIMEOUT = 0
This will very quickly and silently (fade to black) bring you to your login screen, where you can place a splash. Your distro may show it's own splash briefly, which you can change if you like.
This yeilds a professional clean boot sequence, without all the usual linux warts and wrinkles. (Like OSX and Windows).
I personally use Ubunutu with LXDE, and have a clean splashy boot in under 3 seconds, even on older hardware.