If i have a software implementation and if also have a graphic card which supports opengl , then which of these is used by the opengl?
This is both a simple and a complicated question. The simple answer is that OpenGL neither knows nor cares. OpenGL is not a thing; it is a document. A specification. Implementations of OpenGL are things.
Which brings up the complicated part. How you talk to an OpenGL implementation depends on what platform you live on. MesaGL can be compiled as nothing more than a library you link to.
If you want hardware acceleration, then you now have to deal with the OS, because the OS owns the GPU. Mesa as a driver is implemented through the glX system. It hooks into X-windows and X-windows' OpenGL context creation functions can give you a context that is implemented by software Mesa drivers. Or by hardware Mesa drivers. If you're using other drivers, then they too hook into X-windows. These are all tied into X-windows "displays".
On Windows, it's much simpler. There is precisely one ICD driver. If it's installed, and you use a pixel format that it supports (aka: something reasonable), then you get hardware accelerated OpenGL through it. If it isn't you get Microsoft's software implementation.
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I'm started looking for docs for OpenGL ES learning, I came across lot of links. one of them has explained like "OpenGL need to be supported by the vendors of Graphics Cards (like NVidia) and be implemented by the OS's vendors (like Apple in his MacOS and iOS) and finally, the OpenGL give to us, developers, a unified API to work with".
what does it mean by?
OpenGL need to be supported by the vendors of Graphics Cards (like NVidia)
Is it something different to normal code libraries execution?
be implemented by the OS's vendors (like Apple in his MacOS and iOS)...
Is this OS's vendor specific?
If all implementation was done by vendors, what does actually OpenGL ES will do?
I was thinking OpenGLES is a library, which needs to install in required OS and using the specific EGL API's, we need to call them? isn't it?
finally the OpenGL give to us, developers, a unified API to work with
If Os itself developing everything, why to go for OpenGL ES?
Please explain, possibly with an example.
Unlike his name suggests, OpenGL is not a library. Or better, it is cause some symbols for the functions you use need to be linked to the executable.
But OpenGL is a standard de facto library, and a great part of the OSes have a good part of the implementation in their kernel. OSX and iOS provide the OpenGL.framework and GLKit.framework to interface with OpenGL
Architecture Review Board ARB just gives specification of OpenGL. This means It tells what should be name of function which parameters it should accept and what is desired behavior. All the Graphics card vendors take this specification and implement this api. Here function interface and high level working is defined by ARB but internal implementation of API is done depending upon the hardware of vendor. Now this OpenGL API goes into driver. Drivers are generally implemented as Operating system interface part and hardware interface part. So Operating system also need some support for this driver.
I understand that AMD created an alternative implementation of OpenCL that runs on x86 CPUs. This is very useful from the standpoint of simplified debugging. Unfortunately, OpenCL isn't an option for me.
Are there any Open GL x86 implementations in existence? This would greatly ease my development process, at the cost of some CPU time, of course. I would then run the same code on a GPU, later, with no changes necessary.
Mesa might be an option for you.
From their website:
Mesa is the OpenGL implementation for several types of hardware made by Intel, AMD and NVIDIA, plus the VMware virtual GPU. There's also several software-based renderers: swrast (the legacy Mesa rasterizer), softpipe (a gallium reference driver) and llvmpipe (LLVM/JIT-based high-speed rasterizer).
When using Mesa you can set the LIBGL_ALWAYS_SOFTWARE environment variable, which will cause Mesa to "always use software rendering".
OpenGL is not an instruction set, neither is it a library. It's a drawing API for interfacing with GPUs (yes there are software based rasterizers like Mesa softpipe). Most computers you can find these days support OpenGL.
When you use the OpenGL API it's not like your OpenGL calls get "translated" into a special instruction set for the GPU that's then part of your program. OpenGL operations will just create calls that eventually end up in a device driver, just like reading or writing to a file.
This question already has answers here:
How does OpenGL work at the lowest level? [closed]
(4 answers)
Closed 9 years ago.
We all know windows provide a generic OpenGL driver. But some display card vendors provider specific openGL driver. I am wondering how OS to choose which driver to use?
There are WGL functions for getting pointers to appropriate functions of newer OpenGL. Windows chooses the GPU arbitrarily when creating the context.
So, when you, for example, request a 4.3 core context it looks at the list of drivers, says that the one will handle this particular context, and then all wgl calls are made so that they load appropriate functions from the particular driver's dll.
The easiest platform to explain how this works is Microsoft Windows. They have an "Installable Client Driver" (ICD) model, where the Windows SDK provides the bare minimum OpenGL functionality (OpenGL 1.1) and an extensible window system interface (WGL).
When you create your context using the WGL API in Microsoft Windows, you can enumerate all of the pixel formats for a specific device. Some pixel formats will be hardware accelerated and some will use the fallback software OpenGL 1.1 reference implementation. If you get a hardware accelerated format, all of your OpenGL commands will be handled by the graphics card driver and you will have a set of extensions to both GL and WGL that are not available in the reference (1.1) implementation.
This is why so much of modern OpenGL has to be handled through extension loading on Microsoft Windows, at the lowest level you only get OpenGL 1.1 and for anything newer than that, you have to ask the driver for the address of the function you want to use.
Many platforms have a similar system with respect to hardware/software co-existence. Mac OS X is even trickier, because you can start out with a hardware accelerated OpenGL implementation but call the wrong function (one that cannot be implemented in hardware on the installed GPU) and it will throw you off the "fast path" and fallback to software.
The nice thing about Mac OS X, however, is that this fallback only applies to individual stages of the pipeline. It will go back to hardware acceleration for the next stage as long as everything can be implemented in hardware. The beauty is that in OS X, the software implementation of OpenGL is complete (e.g. a 3.2 context will support the entire OpenGL 3.2 feature set even if doing so requires partial/full software implementation). You do not lose functionality if the GPU does not support something, just a LOT of performance. This is in huge contrast to Windows, where none of modern OpenGL has a software fallback.
Some virtual machines do not have displayed card at all. I am wondering OpenGL and DirectX can be simulated by software totally or not?
OpenGL and DirectX are just APIs. The actual implementation may be done in hardware or software. The OpenGL interface DLL shipped by Windows contains a OpenGL-1.1 software rasterizer. The OpenGL implementation used on Linux, Mesa3D, also contains a software rasterizer fallback, implementing OpenGL-2.1.
Direct3D can be implemented in software emulated as, but normally isn't.
The simple answer is yes, and companies like Adobe do just that.
Take a look at SwiftShader:: http://transgaming.com/business/swiftshader
I have to used it before and it runs quite well.
I've been thinking of making an additional wrapper for my project to use OpenGL rather then Allegro. I was not sure which OpenGL version to go for since I know that some computers cannot run recent versions such as v4.4. Also, I need a version which compiles no problem in Linux, Windows, Mac.
You'll want to look at what kinds of graphics cards will be available on your target systems and bear some details in mind:
OpenGL up to 1.5 can be completely emulated in software in real time on most systems. You don't necessarily need hardware support for good performance.
OpenGL 1.4 has universal support. Virtually all hardware supports it.
Mac OS X only supports up to OpenGL 2.0 and OpenGL 2.1, depending on OS version and hardware. Systems using GMA950 have only OGL1.4 support. Mac OS X Lion 10.7 supports OpenGL 3.2 Core profile on supported hardware.
On Linux, it's not unusual for users to specifically prefer open source drivers over the alternative "binary blobs," so bear in mind that the version of Mesa that most people have supports only up to about OpenGL 2.1 compatibility. Upcoming versions have support for OpenGL 3.x. Closed-source "binary blobs" will generally support the highest OpenGL version for the hardware, including up to OpenGL 4.2 Core.
When considering what hardware is available to your users, the Steam hardware Survey may help. Note that most users have DirectX 9-compatible hardware, which is roughly feature-equivalent to OpenGL 2.0. Wikipedia's OpenGL article also specifies what hardware came with initial support for which versions.
If you use a library like GLEW or GLEE or any toolkit that depends on them or offers similar functionality (like SFML, or even Allegro since 4.3), then you'll not need to concern yourself with whether your code will compile. These toolkits will take care of the details of enabling extensions and providing all of the symbols you need.
Given all of this, I'd suggest targeting OpenGL 2.1 to get the widest audience possible with the best feature support.
Your safe bet is OpenGL 2.1, it needs to be supported by the driver on your target system though. OpenGL ES, used on several mobile platforms, is basically a simplified OpenGL 2, so even porting to those would be fairly easy. I highly recommend using libGlew as VJo said.
It's less about operating systems, and more about video card drivers.
I think 1.4 is the highest version which enjoys support by all consumer graphics systems: ATI (AMD), nVidia, and Intel IGP. Intel is definitely the limiting factor here, even when ATI or nVidia doesn't have hardware support, they release OpenGL 4.1 drivers which use software to emulate the missing features. Not so with Intel.
OpenGL is not a library you usually compile and ship yourself (unless you're a Linux distributor and are packaging X.Org/Mesa). Your program just dynamically links against libGL.so (Linux/BSD), opengl32.dll (Windows, on 64 Bit systems, it's also calles opengl32.dll, but it's in fact a 64 Bit DLL) or the OpenGL Framework (MacOS X). This gives your program access to the system's OpenGL installation. The version/profile you want to use has no influence on the library you link!
Then after your program has been initialized you can test, which OpenGL version is available. If you want to use OpenGL-3 or 4 you'll have to jump a few additional hoops in Windows to make full use of it, but normally some kind of wrapper helps you with context creation anyway, boiling it down to only a few lines.
Then in the program you can implement multiple code paths for the various versions. Usually lower OpenGL verion codepaths share a large subset with higher version codepaths. I recommend writing new code in the highest version available, then adding additional code paths (oftenly just substitutions which can be done by C preprocessor macros or similar) for lower versions until you reach the lowest common denominator of features you really need.
Then you need to use OpenGL 1.1, and use needed (and supported) functions through the use of wglGetProcAddress (on windows) or glXGetProcAddress (on linux).
Instead of using those two functions, you can use GLEW library, which does that for you and is cross platform.