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Since Qt can handle in normal way OpenGL, it is cross-platform, can handle mouse, keyboard, gamepad etc. What are the disadvantages of using Qt with OpenGL instead using OpenGL with extensions?
What are the disadvantages of using Qt with OpenGL instead using OpenGL with extensions?
Your question is malformed. Nothing stops you from using Qt with OpenGL and with OpenGL extensions.
You can use Qt to manage the OpenGL window, while using direct OpenGL commands with extension to render. You are not required to use Qt's OpenGL interface to render in an OpenGL window.
Qt does not provide "additional opengl functionality." It cannot provide "additional opengl functionality." It isn't part of OpenGL, so it can't make OpenGL features magically appear.
There are no OpenGL extensions for mouse, keyboard, gamepad, or any of the other things Qt handles. Qt's windowing functionality and OpenGL extensions are two completely different things. And they are completely orthogonal; nothing stops you from using Qt+OpenGL and OpenGL extensions at the same time.
Well, unless you stop yourself. See, Qt has this OpenGL abstraction layer. This is a set of wrapper classes around OpenGL: QtOpenGLShaderProgram, QtOpenGLVertexArrayObject, and the like. If you use that, you don't directly make OpenGL calls; you make Qt calls that make OpenGL calls for you.
If your question is whether to use Qt+OpenGL directly vs. using Qt's OpenGL abstraction layer, that's a different matter.
The first problem is that Qt's abstraction layer is bound to OpenGL ES 2.0. While it occasionally offers features that ES 2.0 can't do, it is primarily intended as a class-ified implementation of ES 2.0. So by using ES 2.0, you're effectively giving up using lots of desktop OpenGL features.
Not "extensions"; core features.
For example, you cannot use integers for vertex attributes with Qt's abstraction. The QtOpenGLShaderProgram class doesn't allow it. All of its setAttributeBuffer calls assume that you're calling glVertexAttribPointer. It has no mechanism for calling glVertexAttribIPointer. And that has been core desktop OpenGL for nearly a decade.
Note that this is just one feature. Other things Qt doesn't have wrapper class support that are part of core desktop OpenGL (this is not a comprehensive list):
Separate programs
Sampler objects
Separate attribute formats
These are not bleeding-edge hardware features; most of them have been around for half a decade.
QtOpenGLFunctions is similarly limited to OpenGL ES versions. That leaves plenty of non-extension desktop GL stuff on the table that cannot be used through their abstraction.
Also, because Qt's abstraction is around ES 2.0, it doesn't care about core OpenGL contexts. For example, it still has non-buffered vertex attributes (setAttributeArray). That's not legal in core OpenGL, and again hasn't been legal for nearly a decade.
So if you want to actually use core desktop OpenGL functionality, the Qt abstraction layer is out.
Then, there are places where Qt's abstraction just doesn't match how OpenGL works.
For example (and this is a personal pet-peeve of mine), QtOpenGLBufferObject is typed. That is, the binding type is part of the object. This is not how buffer objects work!
OpenGL buffer objects aren't typed. It is perfectly legal to perform an asynchronous glReadPixels into a buffer, then bind the same buffer for use as vertex data. That's not possible with Qt's class abstraction. And it's not like this is something specific to desktop GL; OpenGL ES works the same way.
Similarly, for reasons best known to themselves, they put the vertex attribute specification functions (the equivalent to glVertexAttribPointer) in QtOpenGLShaderProgram. Why are they there? While vertex attributes do have an indirect connection to a program, they're not a direct part of the conceptual program interface. OpenGL doesn't work like that.
So those are the biggest problems with Qt's abstraction layer. If you can live within those restrictions, feel free to use it. For people making desktop OpenGL applications, they may be too restrictive.
You (OP) wrote in a comment to a different answer:
Extensions provide functionality that the core of OpenGL doesn't provide when Qt itself won't be created for providing additional opengl functionality. It was like a addon for users.
I think you completely misunderstood what OpenGL extensions are and how they work. OpenGL extensions allow to add new features to OpenGL (which might actually be included into a later core version) and/or to expose vendor specific functionality like access to special GPU functions present only for a very specific narrow range of GPUs.
Qt on the other hand offers a framework for applications that deals with operating system specifics in a portable way. Qt and OpenGL are completely orthogonal to each other and nothing, that OpenGL extensions do in any way resembles what Qt does. Qt has a OpenGL integration module, that – among other things – will also load OpenGL extensions if you ask it to; but that doesn't make it a "Qt" thing.
I think you are missing the point. OpenGL (including its extensions that provide some perks that the plain OpenGL does not) is "just" a graphics library intended for rendering 2D and 3D. Qt on the other hand is much more. OpenGL in itself doesn't provide anything but rendering. You can't even create a window (as what you are used to in Windows/Linux) with it. In order to add any sort of handling of the user's input you need an extra layer which Qt (and many other similar frameworks) provides - integration into the window manager of the OS, handling of mouse and keyboard events etc. Qt does also support the OpenGL extensions so you don't have to throw these away if you want to use them.
Whether you need Qt for your OpenGL (with or without the extensions your system supports) tasks or not is something you need to decide for yourself. Qt does offer many nice features that will help you make your OpenGL interaction great however it is a huge overhead and depending on your target system you may have to use a smaller framework with a smaller memory (incl. persistent storage for all the library files) footprint and CPU usage. Other popular choices are GLFW, freeglut and SDL/SDL2 all of which provide at least the basics (window creation and mouse/keyboard handling) to get your application up and running.
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QML as per my knowledge does the same thing as OpenGL, right? So can I completely replace OpenGLwith QML ?
Whats the basic difference between QML and OpenGL?
When does people prefer QML over OpenGL and vice versa?
Your knowledge is incorrect, QML and OpenGL are two completely different things, the first is a declarative language the second is a graphics API.
QtQuick which uses QML usually uses OpenGL for its graphics, but that's a back-end you don't have any access to (it actually got a little more accessible in the recent releases but I expect not many people will go into tweaking that, and even if they did, it would be in C++, not QML).
There is Qt3D, which has a QML API, but it is just some basic stuff and it is high level - by no means a substitute to OpenGL which is very low level. That means it will be much easier to put some 3D models, cameras, materials and such with Qt3D, things you'd normally not do in OpenGL directly, but with an API built on top of OpenGL.
I'm using QWebEngine to display some webpages. Unfortunately it uses OpenGL internally - which leads to a crash on some graphics adapters (one can see the driver-DLL as the reason for the crash easily). As a second caveat it is not possible to catch this crash by a try-catch-block.
So my question: how can one force QWebEngine to use software rendering only and to not to use OpenGL?
Thanks!
I assume you're on Windows, and are using the official Qt binaries, and are using Qt 5.5 or newer. These allow to switch between Desktop OpenGL, ANGLE (Direct X) and software rasterization at runime.
It should be therefore enough to set the QT_OPENGL environment variable to either "angle" (to use the DirectX backend) or "desktop". To hardcode this you can set the Qt::AA_UseOpenGLES or Qt::AA_UseSoftwareOpenGL application attributes.
If you use WebEngine through Qt Quick, you can also use the Qt Quick 2D renderer.
I wonder what is the bounds of Qt's perimeter. I know for exemple that it can specify types (such as qint or QString), and I know it cannot get system informations such as CPU Usage or Memory Usage.
My question is about the limits of Qt.
Is it correct that Qt can only interact with what is inside the project but not with what is outside (I mean system-related) ?
You can get information about operating system with QSysInfo class, if you are looking for this. This is one example, I am sure there are other helper classes. I think you should use other libraries for information like CPU usage etc, see here and also this question.
QT is nothing more/nothing less then a GUI C++ cross-platform framework. It's doesn't really have a perimeter, it has certain cross-platform functions implemented (like widgets/frames/controls a lot of other things). And within it's own functionality it provides (As being mentioned above) QSysInfo class, but you are free to add any OS dependent (if you target your application for particular platform) or cross-platform solutions for whatever tasks you need - hardware info/OS monitoring/etc..
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Closed 9 years ago.
Since there are two ways to use OpenGL with Qt 5 (QOpenGL/QtOpenGL wrapper and regular OpenGL API), I wonder what are the limitations of each one. Could someone tell if there are limitations with QOpenGL wrapper that I should be aware of?
The reason I am asking this is because I don't want to start using QOpenGL wrapper and find out that I can't use the full capability of OpenGL API. Does anyone have experience with both and could provide some hints in terms of capability, performance and ease of use?
I don't want to start using QOpenGL wrapper and find out that I can't use the full capability of OpenGL API
Well, Qt 5.0's OpenGL wrappers are built on top of the OpenGL ES (Embedded Systems) 2.0 specification which is essentially a watered down version of the desktop OpenGL 3.0 specification. Qt chose this specification to facilitate portability as it is widely supported by mobile platforms in addition being supported on nearly all modern PCs. If you choose to use the Qt wrappers you have to work around the shortcomings of the OpenGL ES 2.0 specification which, for the most part, fall into the following categories:
No fixed-function pipeline capabilities. (no transformation stack, glBegin,glEnd,glLightf,etc..)
No support for advanced OpenGL 3+ capabilities or support only in extensions. (texture buffer objects, compute shaders, atomic load-store textures, tessellation shaders, uniform buffer objects etc..)
Lack of certain texture formats (integer textures, image textures, etc..)
Small differences in GLSL syntax & semantics. (lack of layout qualifiers, data precision requirements via highp, lowp declarations, etc..)
Lack of some convenience methods. (glBlitFramebuffer,glMultiDrawArrays, glDrawRangeElements, etc..)
For a full description of the OpenGL ES 2.0 specification look here.
However, This lack of features does not mean that the Qt wrappers can not accomplish what you need. Although OpenGL ES 2.0 is missing a lot of helpful functionality, you can still accomplish 99% of what the full desktop OpenGL specification would allow. If you decide to utilize a desktop OpenGL specification via custom wrappers, Qt can still manage the creation & windowing of desktop OpenGL contexts through the use of the QGLFormat class.
Keep in mind that if you decide to use desktop OpenGL wrappers, and utilize these within a Qt application, some classes provided by Qt may interfere with the operation of your custom wrappers. For example, QPainter operations on a QGLWidget may utilize functionality of the OpenGL ES specification and might interfere with the operation of your wrapper objects.
Personally, I prefer to use custom OpenGL wrappers as I greatly prefer the desktop OpenGL specifications as the feature sets are better defined and they provide more options to tackle a problem with. On the other hand, Qt 5 provides some absolutely fantastic architectures for making quick, powerful dynamic user interfaces using OpenGL ES. (Through by QtQuick 2 and QML)
Which API suits your needs best essentially comes down to whether or not you are targeting embedded or mobile platforms (in which case your forced to use OpenGL ES), and whether you are willing to sacrifice additional development time writing and maintaining custom OpenGL 3+ wrappers.
I'm searching for a simple library for creating GUI that can have:
a portable codebase across different compilers and OS
can be easily extended to a new platform if that platform it's not natively supported
are real library and not just a collection of #define, tools and other un-portable and non-standard things.
So far the "best" match is QT that is just the opposite of each one of this 3 points, especially the 3rd one (moc compiler and #defines ... ).
I also do not need data structures and 10000 extra functions, i just need to code a portable GUI, hipotetically i don't even need a signal slot library included because I can handle signals with third part libraries.
If there is no such lib available can you point me to a resource where I can learn about the OS specific basics about Widgets and Windows ?
I never used it, but I would suggest looking into IUP
From what I read this would fit the bill quite well. The project is also quite active. Though it is probably not too pretty.