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.
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I have been wanting to make a game in OpenGL, c++ for a while now and i would love some explanation on how exactly it works and what it is.
Can computer graphics be made without OpenGL ? most of the tutorials i have seen online show how to use OpenGL for the most basic graphics drawing, it is possible to directly interface with your GPU ?
How does OpenGL work on different CPU's and Operating systems ? As far as i know languages like c++ must be recompiled if they want to be used on an ARM processor and the such, is this not the case for GPU's in general ?
If you can indeed make graphics without OpenGL, does anybody still do this ? how much work and effort does OpenGL save in general and how complex are the systems that OpenGL facilitates for us?
Are there other libraries like OpenGL that are commonly used ? if not, will new libraries eventually come and take it's place or is it perfect for the job and not going anywhere ?
How exactly it works and what it is?
OpenGL defines an interface that you as a programmer can use to develop graphics programs (API). The interface is provided to you in form of header files that you include to your project. It is meant to be multiplatform, so that you can compile your code that uses OpenGL on different operating systems. People that manage the OpenGL specification do not provide the implementation of specified functionality. That is done by the OS and hardware vendors.
Can computer graphics be made without OpenGL?
Yeah, sure. You can e.g. calculate the whole image manually in your program and then call some OS-specific function to put that image on the screen (like BitBlt in Windows).
How does OpenGL work on different CPU's and Operating systems?
Each OS will have its own implementation of OpenGL specification that will usually call the hardware drivers. So let's say you have machine with Windows OS and Nvidia graphics card. If you run some program that calls glDrawElements it will look like this:
your_program calls glDrawElements
which calls glDrawElements implementation written by people from Microsoft
which calls Nvidia drivers written by people from Nvidia
which operates the HW
If you can indeed make graphics without OpenGL, does anybody still do this?
Yeah sure. Some people might want to implement their own rendering engine from ground up (although that is really hardcore thing to do).
Are there other libraries like OpenGL that are commonly used ? if not, will new libraries eventually come and take it's place or is it perfect for the job and not going anywhere ?
Sure. There is DirectX that is maintained by Microsoft and targets only Windows platforms and the Vulkan that can be seen as successor to OpenGL.
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.
As I understand GPU vendors defined standard interface to be used by OS Developers to communicate with their specific driver. So DirectX and OpenGL are just wrappers for that interface. When OS developers decide to create new version of Graphic API , GPU vendors expand their interface (new routines are faster and older ones are left for compatibility issues) and OS developers use this new part of interface.
So, when it is said that GPU vendors' support for DirectX is better than for OpenGL, does it simply mean that GPU vendors primarily take into account Microsoft's future plans of developing DirectX API structure and adjust future development of this interface to their needs? Or there is some technical reasons before this?
As I understand GPU vendors defined standard interface to be used by OS Developers to communicate with their specific driver. So DirectX and OpenGL are just wrappers for that interface.
No, not really. DirectX and OpenGL are just specifications that define APIs. But a specification is nothing more than a document, not software. The OpenGL API specification is controlled by Khronos, the DirectX API specification is controlled by Microsoft. Each OS then defines a so called ABI (Application Binary Interface) that specifies which system level APIs are supported by the OS (OpenGL and DirectX are system level APIs) and what rules an actual implementation must adhere to, when being run on the OS in question.
The actual OpenGL or Direct3D implementation happens in the hardware's drivers (and in fact the hardware itself is part of the implementation as well).
When OS developers decide to create new version of Graphic API , GPU vendors expand their interface
In fact it's the other way round: Most of the graphic APIs specifications are laid out by the graphics hardware vendors. After all they are close to where the rubber hits the road. In the case of Khronos the GPU makers are part of the controlling group of Khronos. In the case of DirectX the hardware makers submit drafts to and review the changes and suggestions made by Microsoft. But in the end each new APIs release reflects the common denominator of the capabilities of the next hardware generation in development.
So, when it is said that GPU vendors' support for DirectX is better than for OpenGL, does it simply mean that GPU vendors primarily take into account Microsoft's future plans of developing DirectX API structure and adjust future development of this interface to their needs?
No, it means that each GPU vendor implements his own version of OpenGL and the Direct3D backend, which is where all the magic happens. However OpenGL puts a lot of emphasis on backward compatibility and ease of transition to newer functionality. Direct3D development OTOH is quick in cutting the ties with earlier versions. This also means that full blown compatibility profile OpenGL implementations are quite complex beasts. That's also the reason why recent versions of OpenGL core profiles did (overdue) work in cutting down support for legacy features; this reduction of API complexity is also quite a liberating thing for developers. If you develop purely for a core profile it simplifies a lot of things; for example you no longer have to worry about a plethora of internal state when writing plugin.
Another factor is, that for Direct3D there's exactly one shader compiler, which is not part of the driver infrastructure / implementation itself, but gets run at program build time. OpenGL implementations however must implement their own GLSL shader compiler, which complicates things. IMHO the lack of a unified AST or immediate shader code is one of the major shortcomings of OpenGL.
There is not a 1:1 correspondence between the graphics hardware abstraction and graphics API like OpenGL and Direct3D. WDDM, which is Windows Vista's driver model defines things like common scheduling, memory management, etc. so that DirectX and OpenGL applications work interoperably, but very little of the design of DirectX, OpenGL or GPUs in general has to do with this. Think of it like the kernel, nobody creates a CPU specifically to run it, and you do not have to re-compile the kernel everytime a new iteration of a processor architecture comes out that adds a new subset of instructions.
Application developers and IHVs (GPU vendors, as you call them) are the ones who primarily deal with changes to GPU architecture. It may appear that the operating system has more to do with the equation than it actually does because Microsoft (more so) and Apple--who both maintain their own proprietary operating systems--are influential in the design of DirectX and OpenGL. These days OpenGL closely follows the development of commodity desktop GPU hardware, but this was not always the case - it contains baggage from the days of custom SGI workstations and lots of things in compatibility profiles have not been hardware native on desktop GPUs in decades. DirectX, on the other hand, has always followed desktop hardware. It used to be if you wanted an indication of where desktop GPUs were headed, D3D was a good marker.
OpenGL is arguably more complicated than DirectX because until recently it never let go of anything, whereas DirectX radically redefined the API and stripped legacy support with every iteration. Both APIs have settled down in recent years, but D3D still maintains a bit of an edge considering it only has to be implemented on a single platform and Microsoft writes the one and only shader compiler. If anything, the shader compiler and minimal feature set (void of legacy baggage) in D3D is probably why you get the impression that vendors support it better.
With the emergence of AMD Mantle, the desktop picture might change again (think back to the days of 3Dfx and Glide)... it certainly goes to show that OS developers have very little to do with graphics API design. NV and AMD both have proprietary APIs on the PS3, GameCube/Wii/WiiU, and PS4 that they have to implement in addition to D3D and OpenGL on the desktop, so the overall picture is much broader than you think.
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.
What is the difference between OpenGL and Direct3D? Are they truly different implementations to accomplish the same things (like Java and Mirosoft's CLR [.NET])?
They are very different graphics API's. But it's fair to say they mostly accomplish the same thing. DirectX is probably the API of choice if you are developing a game under windows (or a game for XBOX), and OpenGL is the choice if you want cross-platform support. Mac OS uses GL, as does the iPhone, for example, and many windows games also support OpenGL.
Because OpenGL was developed over a long time and 'by committee', it comes with a lot of baggage - the API has some older options that aren't really relevant today. That's one of the reasons for OpenGL ES; it cuts out all the junk and makes for an easier target platform.
DirectX on the other hand is controlled by Microsoft, and as such it has a more 'modern' feel to it (it's based on COM components, so is highly object oriented). MS often update the API to match new hardware.
Sometimes you don't have the luxury of choice (iphone for example can't run DX). But often it just comes down to personal preference/experience. If your a long-time graphics programmer, you tend to get pretty familiar with both...
Google is your friend in this case...there's a good Wikipedia article contrastring the two libraries:
Comparison of OpenGL and Direct3D
If memory serves, OpenGL was the open implementation before Direct3D came out. Direct3D was then based off of OpenGL...but quickly diverged and became it's own distinct library.
UPDATE
Looks like my memory is shot...
Direct3D was developed independtly of OpenGL.
Direct3D and OpenGL are different API's used to accomplish the same thing.
The major differences between D3D and GL is that D3D is Object Oriented and GL is not.
D3D9 and GLES2 basically have the same features. In fact if you plan on using OpenGL and do not need any GL3 or GL4 features you should base all you code on the GLES2 API(all GLES2 features are in GL2, but not the other way around).
If possible you should always use D3D over GL on windows, as multithreading and driver support is flaky. Take the netbooks for example, they support D3D's HLSL at ShaderModel 2 but don't support the equivalent for GLSL, they only support a fixed pipeline for GL.