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OpenGL Newbie: 2 fundamentally different types of openGL programs?

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Hello. Im a beginner to OpenGL. Ive been downloading sample programs with source code to read through them and Ive noticed that there seems to be 2 distinctly different ways to create an opengl program. One way seems to require less source code and opens a "dos box" along with the opengl window itself. Looking at the source code, the main function is defined as "int main()". This type of opengl program relies on functions such as these: glutDisplayFunc(Display); glutReshapeFunc(reshape); glutKeyboardFunc(KeyDown); to handle displaying, reshaping the window, and pressing a key, respectively. The other method involves more source code and does not create the "dos box" as mentioned above. I think that for this reason alone it is a better method. The main function is defined like this "int WINAPI WinMain(..." instead of just "int main()". There doesnt seem to be glut*() functions to handle events. Instead, the WndProc() function uses a SWITCH statement to catch events like: WM_KEYDOWN WM_MOUSEMOVE WM_SIZE What I would like to know is: which method is better? If the answer to that question is "it depends", then what does it depend on? Which method should I use in which situation. Being a beginner, all this stuff is confusing enough as it is, and I would prefer to only have to learn one method if possible. Thanks in advance! Its not my fault I''''m the biggest and the strongest; I don''''t even exercise.

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I personally prefer the Win32 method. This is because not only is it free of that annoying dos window but it also leaves you already set to accept input from the keyboard and mouse. Don''t be intimidated by the amount of code (its more simple Win32 than it is OpenGL). Once you learn it and write your own class to put it in you''ll never have to write the code to open the dos-less window again.

If it ain''''t broke, your not testing it hard enough

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Thanks! I was hoping someone would say something along those lines. So just to be sure, there could never be a situation where I would need the other method instead of win32 right?

thanks again!

Its not my fault I''''m the biggest and the strongest; I don''''t even exercise.

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The direct Win32 method is generally not good. It can be used, but it will totally break platform independance, and it can be hard to maintain.

GLUT is better for small projects. It''s easy, clean, and totally portable, since it hides platform specific code. In fact, it also does the ''Win32 stuff'', it''s just not visible.

The best method is a wrapper class. You basically use the Win32 initialization, but instead of using it directly, you put a compatibility layer between it and your code. That way, it''s easier to maintain, and you can add different platforms as you go on.

If you can, stay with GLUT. If you can not (because glut doesn''t offer the functionality you need), then use the Win32 method, but make sure to isolate the Win32 code. Don''t spill it all over your program. Put it into a separate class or function.

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When you say that it will break platform independance, do you mean that if i use the Win32 method, that my program will only run on Win32 machines? Or only my machine? or what? Ive always been curious about what people meant when they say "platform independance". What exactly is a platform? Do they mean operating system?

Is there any way to get rid of that "dos box" when using the GLUT method? I feel that it makes my project look very unprofessional (not that it looks very good on its own anyway, but you know

Could you please point me to some more information about this wrapper class you speak of? I only vaguely understand what you mean by that, and have no idea how to actually go about implementing it.

Thank you so much !

Its not my fault I''''m the biggest and the strongest; I don''''t even exercise.

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Platform independance is usually a term to define source code that will compile and run under different Operating systems (like Windows, Linux etc...). The easiest way in my opinion to accomplish this is with #define''s and #ifdef''s. For example, lets say that you want to write a "platfrom independance" function that creates a window under Win32 and under Linux :

void MyCreateWindow (int width, int height)
{
#ifdef _WINDOWS_BUILD_
... code to create a window using WIN32...
#endif

#ifdef _LINUX_BUILD_
... code to create a window under Linux...
#endif
}

when you compile the above code with the "_WINDOWS_BUILD_" definition, it will create the Win32 code and with "_LINUX_BUILD_" compiler will create linux code.

As for getting rid of the dos box, I don''t know a method to avoid it. Use Win32.

Someg.

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quote:

When you say that it will break platform independance, do you mean that if i use the Win32 method, that my program will only run on Win32 machines? Or only my machine? or what? Ive always been curious about what people meant when they say "platform independance". What exactly is a platform? Do they mean operating system?


Operating system (Windows, Linux, BeOS, ...) and machine architecture (x86, Mac, SGI, ...). True platform independance means, that your code will compile without changes and run on all computers that support the language and API (in your case OpenGL), regardless of OS, CPU and graphics system.

Eg. if you write a portable and platform independant game, then it will compile and run under a Windows PC, a Macintosh, and even a SGI or Cray supercomputer.

GLUT is portable. Win32 is not, it will only run on Windows PCs (and depending on what Win32 functions you call, it might even only run on a specific version of Windows).

quote:

Could you please point me to some more information about this wrapper class you speak of? I only vaguely understand what you mean by that, and have no idea how to actually go about implementing it.


A wrapper is a kind of container. It isolates platform specific code (ie. code than can only run on a certain OS or computer, in your case all the Win32 code). GLUT is a wrapper, but your can write your own, if GLUT doesn't fit your needs.

Think of it as a black box. Once it is implemented, you don't care about it inner workings. It is totally separate from the rest of your game or application. To open a window, for example, you would call a function like 'OpenWindow( ... )'. The blackbox (the wrapper) will then open a window, using a method that is appropriate for the OS and CPU that your game is currently running on. You don't need to care about that anymore in your game.

In straight C, this wrapper is commonly implemented as a collection of functions in a seperate source file, often even in a library. You have functions to open and close windows, to handle keyboard and mouse, etc. The details are done the way that Someg demonstrated above, with #ifdef's.

In C++, it is often implemented using a special class hierarchy with a common standard interface. Thus the name 'wrapper class'.

If you don't want to implement your own, there are lots of third party wrapper classes and libraries available. A very good one is SDL. It's much more sophisticated than GLUT. Besides graphics related functions, it also contains wrappers for input (keyboard, mouse), music/sound handling and others. It's easy to use, platform independant and free. You should check it out.

/ Yann

[edited by - Yann L on August 29, 2002 8:36:10 PM]

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quote:
Original post by Yann L
True platform independance means, that your code will compile without changes and run on all computers that support the language and API (in your case OpenGL), regardless of OS, CPU and graphics system.

[offtopic]
"True platform independence" doesn''t exist - at least not for applications that do anything remotely useful. It is approximated by writing libraries and abstraction layers that contain conditionally-compiled platform-specific code.

Furthermore, platform independence is of no use to some. Advocating certain methods because they solve problems the user doesn''t have complicates the matter unnecessarily. In this case, Andre the Giant should be encouraged to abstract his Win32 (and OpenGL!) code because it is maintainable, compact and good programming practice. That it is also portable is not (yet) of any benefit to him, and only serves to confuse him.
[/offtopic]

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True low level binary platform independance is of course impossible - different machine level opcodes and system architecture will ruin it in the first place.

But I was referring to the popular use of the term 'platform independance' (even if it might not be the exact literary one): independance on source level, using wrapper libraries.

I would classify a C/C++ program using OpenGL and GLUT as totally platform independant (not the required libraries, of course). In this context, 'total' refers to platforms supporting the required language (C/C++), the graphics API (OGL) and the interface wrapper (GLUT). Almost all systems in usage today do that.

Platform independance is not required by everyone, that's a fact. But since he asked about it, I replied

Besides the used platform or OS, abstracting system level functions is always a good idea. The code will be cleaner, and much easier to maintain. The worst thing is having code that is intermixed with system calls every few lines. That's a mistake lots of beginning programers do, and I think it is a good idea to practice abstraction from the beginning on. It simply is good coding style.

And if abstraction brings portability for free, then this can only be a positive side effect.

[offtopic 2]
This might be a bit personal philosophy, but choosing OpenGL in the first place advocates platform independance, IMO. Not even necessarily architecture independance, but also interoperability between different Windows versions, regarding backwards compatibility (eg. with NT, which is still widely used in the graphics domain). If that is of any importance for Andre the Giant, is questionable, of course
[/offtopic 2]

/ Yann

[edited by - Yann L on August 29, 2002 9:55:03 PM]

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quote:
Original post by Yann L
[offtopic 2]
This might be a bit personal philosophy, but using OpenGL in the first place advocates platform independance, IMO. Not even necessarily architecture independance, but also interoperability between different Windows versions, regarding backwards compatibility (eg. with NT, which is still widely used in the graphics domain).
[/offtopic 2]

[offtopic 3]
OpenGL is rooted in platform independence (an open, accessibly high-level graphics abstraction "language" that resulted from IrisGL, but that''s by the side). Unfortunately, OpenGL is also mired in platform independence. Platform-specific extensions, windowing kits (wgl, glx, etc) and resource acquisition methods (PFDs, etc) contradict this objective, though admittedly to a lesser extent.

The other big problem with OpenGL''s platform independent objectives - not an integral API problem, but rather a shortcoming in the design process - is that the ARB moves slowly to update the API (which necessitated extensions in the first place, which leads to inconsistencies in syntax and functionality per platform, which contradicts the initial objective).

OpenGL is mad cool, though. If and when 2.0 hits, and if it provides solutions (or at least decent attempts at solutions) to these problems, then people like me (read: lazy programmers who don''t care about platform independence) might give it a very serious look. Until then...
[/offtopic 3]

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Andre, I''m sorry for this hijacked thread. If the replies above did not answer your question, then feel free to interrupt us

[offtopic 4]
quote:

Unfortunately, OpenGL is also mired in platform independence. Platform-specific extensions, windowing kits (wgl, glx, etc) and resource acquisition methods (PFDs, etc) contradict this objective, though admittedly to a lesser extent.


This is certainly true, but I don''t think that it is totally possible to avoid those dependencies when creating a portable API. Especially, if it goes over such a wide range of software/hardware combinations as OpenGL (some of them very exotic). There will always be a platform dependend hook somewhere, the only real solution would be a standarized API hook built into every OS itself. That would change the target of interoperability: not the API would need to be made multiplatform, but the OS/architecture would need to adapt to a standard API. I don''t know if this scenario would really be a better alternative. A lot of people would object to it, for obvious reasons.

quote:

The other big problem with OpenGL''s platform independent objectives - not an integral API problem, but rather a shortcoming in the design process - is that the ARB moves slowly to update the API (which necessitated extensions in the first place, which leads to inconsistencies in syntax and functionality per platform, which contradicts the initial objective).


Hmm, every concept has it''s advantages and shortcomings. And open design brings the problem of internal consistency among different vendors, with different views of the market. IP and patents are another important factor to consider here. Although the ARB extensions could be seen as a kind of incremental API update, too few real important functionality has been standarized. This will change with OpenGL 2.0 (hopefully). On the other hand, consider when OpenGL was first introduced - graphics hardware wasn''t even capable of texture mapping at that time. I think it is still interesting to note, how well it has nevertheless managed to stay up to date with modern features. Although OpenGL 1.x has admittedly lost some of it''s open ideals in that process (NV_*, ATI_*, etc).

quote:

OpenGL is mad cool, though. If and when 2.0 hits, and if it provides solutions (or at least decent attempts at solutions) to these problems, then people like me (read: lazy programmers who don''t care about platform independence) might give it a very serious look. Until then...


You could of course use the opposite argument as well: a programmer that does not have to care about platform independence can focus it''s energy onto other parts of the project
It ultimately always depends on your goals, and target markets. And if everything goes well with the OpenGL 2.0 launch, lots of there above mentioned problems will disappear - and we are all waiting for that.
[/offtopic 4]

/ Yann

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noone mentioned sdl www.libsdl.org, its a very good bet to build a opengl app upon + as a bonus its also runs on a few platforms (even the ps2!)

http://uk.geocities.com/sloppyturds/gotterdammerung.html

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quote:
Original post by zedzeek
noone mentioned sdl www.libsdl.org, its a very good bet to build a opengl app upon + as a bonus its also runs on a few platforms (even the ps2!)

http://uk.geocities.com/sloppyturds/gotterdammerung.html


Yes someone did.

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Continuing the unfortunate hijacking of the thread... My apologies to all; this should be a separate thread but it''s hard to move a discussion once it''s started. Again, just stop us if it gets in the way.

quote:
Original post by Yann L
This [OpenGl "mired in platform independence, etc"] is certainly true, but I don''t think that it is totally possible to avoid those dependencies when creating a portable API. Especially, if it goes over such a wide range of software/hardware combinations as OpenGL (some of them very exotic). There will always be a platform dependend hook somewhere, the only real solution would be a standarized API hook built into every OS itself.

Actually, I think that it''s quite possible to write an API that is exactly the same at on all supported platforms. Instead of maintaining these platform-specific "interface" APIs, simply write them into the initialization of OpenGL (for instance) and have their platform-specific implementation hidden from the end user, just like with the rest of the API. SDL is consistent across all platforms, and so is FMOD.

The truly interesting question is how to allow extensions to be made in a fashion that is platform- and vendor-agnostic, standard and than benefits the end-user (the developer) so we can avoid the mechanisms we''ve both mentioned - NV_* and ATI_* being prime examples. I assume this is one of the issues that 2.0 addresses (I haven''t really studied the spec/proposal).

While it can be argued that DirectX doesn''t have platform issues to address (other than the closed-access XBox version), they did take steps to solve version compatibility problems by basing DX on COM. Is it feasible to based OpenGL (or its successor) on (open) object technologies like CORBA? Is it possible to provide some QueryInterface-like functionality for determining exact vendor extensions available, and utilizing them in a cohesive manner (dropping vendor-specific extension names would be one step such that cards from different manufacturers providing the same additional functionality would use the same extension name, removing the burden of writing to specific drivers)? I, for one, sincerely hope so.

quote:

It ultimately always depends on your goals, and target markets. And if everything goes well with the OpenGL 2.0 launch, lots of there above mentioned problems will disappear - and we are all waiting for that.


Amen to that!

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>>they did take steps to solve version compatibility problems by basing DX on COM<<

i was drinking coffie when i read that (with obvious results )

http://uk.geocities.com/sloppyturds/gotterdammerung.html

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This is very against what it seems most people are saying. But in the game programming world - or PC game programming only - wouldn''t it not be so bad to ignore all platforms other than Windows? I mean, it may be good programming practice to do this or that, but if you want to make a killer game and you dont want it to be for any other console than Windows...why not use the Win32 API?

And in general, most games do come out for Windows and nothing else but Windows. This maybe just me, but it also seem like more and more games are just using Direct3D and ignoring OpenGL(this isn''t to start a war).

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quote:
Original post by zedzeek
>>they did take steps to solve version compatibility problems by basing DX on COM<<

i was drinking coffie when i read that (with obvious results )

LOL! But you know what I meant: the reason we have to CoInitialize and QueryInterface is to allow the API interfaces be broken if absolutely necessary without breaking existing code that depended on those interfaces (those who have no idea what I''m talking about, don''t worry; it''s in those static libs you link in). And while it''s not necessarily the most elegant of solutions, it works extremely well.

quote:
Original post by EbonySeraph
This is very against what it seems most people are saying. But in the game programming world - or PC game programming only - wouldn''t it not be so bad to ignore all platforms other than Windows? I mean, it may be good programming practice to do this or that, but if you want to make a killer game and you dont want it to be for any other console than Windows...why not use the Win32 API?

Platforms come and go. Professional shops will receive specs and debug units and dev kits early to allow them deliver content on time for new platforms, but having honed the techniques of platform-agnostic programming and built solid abstraction layers allows your library developers to port your existing tools to new platforms while the rest of your workforce continues using those tools "blindy". Existing, proven and familiar tools can greatly shorten development cycles, which means reduced cost and more time spent on play balancing and QA, which means a better game, which means higher sales, which means more profits to fund further game development.

quote:
Original post by EbonySeraph
And in general, most games do come out for Windows and nothing else but Windows. This maybe just me, but it also seem like more and more games are just using Direct3D and ignoring OpenGL(this isn''t to start a war).

Only Windows developers can afford to ignore OpenGL and use Direct3D (XBox runs on a version of Windows, so it doesn''t count). OpenGL is available in some form on virtually all other platforms, so it''s a very important API. I just wonder whether 2.0 will really respond to the concerns of the developer or whether it''s time for an alternative (don''t take that too seriously; gaining the manufacturer support necessary to be an effective alternative to either D3D or OpenGL is no easy task). Why is this important? Because most games, contrary to your statement, do not come out for "Windows and nothing else but Windows". The cutting-edge PC gaming market still lags behind the console space in terms of grosses and media units. Even Microsoft thinks the PC market will never upset the console space, so it got into that other market with its XBox.

Anyway, I think this thread has drifted far enough.

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      An alternative way to design the API would be to expose command queue and command lists directly. This approach however does not map well to Direct3D11 and OpenGL. Besides, some functionality (such as dynamic descriptor allocation) can be much more efficiently implemented when it is known that a command list is recorded by a certain deferred context from some thread.
      The approach taken in the engine does not limit scalability as the application is expected to create one deferred context per thread, and internally every deferred context records a command list in lock-free fashion. At the same time this approach maps well to older APIs.
      In current implementation, only one immediate context that uses default graphics command queue is created. To support multiple GPUs or multiple command queue types (compute, copy, etc.), it is natural to have one immediate contexts per queue. Cross-context synchronization utilities will be necessary.
      Swap Chain (ISwapChain interface). Swap chain interface represents a chain of back buffers and is responsible for showing the final rendered image on the screen.
      Render device, device contexts and swap chain are created during the engine initialization.
      Resources (ITexture and IBuffer interfaces). There are two types of resources - textures and buffers. There are many different texture types (2D textures, 3D textures, texture array, cubmepas, etc.) that can all be represented by ITexture interface.
      Resources Views (ITextureView and IBufferView interfaces). While textures and buffers are mere data containers, texture views and buffer views describe how the data should be interpreted. For instance, a 2D texture can be used as a render target for rendering commands or as a shader resource.
      Pipeline State (IPipelineState interface). GPU pipeline contains many configurable stages (depth-stencil, rasterizer and blend states, different shader stage, etc.). Direct3D11 uses coarse-grain objects to set all stage parameters at once (for instance, a rasterizer object encompasses all rasterizer attributes), while OpenGL contains myriad functions to fine-grain control every individual attribute of every stage. Both methods do not map very well to modern graphics hardware that combines all states into one monolithic state under the hood. Direct3D12 directly exposes pipeline state object in the API, and Diligent Engine uses the same approach.
      Shader Resource Binding (IShaderResourceBinding interface). Shaders are programs that run on the GPU. Shaders may access various resources (textures and buffers), and setting correspondence between shader variables and actual resources is called resource binding. Resource binding implementation varies considerably between different API. Diligent Engine introduces a new object called shader resource binding that encompasses all resources needed by all shaders in a certain pipeline state.
      API Basics
      Creating Resources
      Device resources are created by the render device. The two main resource types are buffers, which represent linear memory, and textures, which use memory layouts optimized for fast filtering. Graphics APIs usually have a native object that represents linear buffer. Diligent Engine uses IBuffer interface as an abstraction for a native buffer. To create a buffer, one needs to populate BufferDesc structure and call IRenderDevice::CreateBuffer() method as in the following example:
      BufferDesc BuffDesc; BufferDesc.Name = "Uniform buffer"; BuffDesc.BindFlags = BIND_UNIFORM_BUFFER; BuffDesc.Usage = USAGE_DYNAMIC; BuffDesc.uiSizeInBytes = sizeof(ShaderConstants); BuffDesc.CPUAccessFlags = CPU_ACCESS_WRITE; m_pDevice->CreateBuffer( BuffDesc, BufferData(), &m_pConstantBuffer ); While there is usually just one buffer object, different APIs use very different approaches to represent textures. For instance, in Direct3D11, there are ID3D11Texture1D, ID3D11Texture2D, and ID3D11Texture3D objects. In OpenGL, there is individual object for every texture dimension (1D, 2D, 3D, Cube), which may be a texture array, which may also be multisampled (i.e. GL_TEXTURE_2D_MULTISAMPLE_ARRAY). As a result there are nine different GL texture types that Diligent Engine may create under the hood. In Direct3D12, there is only one resource interface. Diligent Engine hides all these details in ITexture interface. There is only one  IRenderDevice::CreateTexture() method that is capable of creating all texture types. Dimension, format, array size and all other parameters are specified by the members of the TextureDesc structure:
      TextureDesc TexDesc; TexDesc.Name = "My texture 2D"; TexDesc.Type = TEXTURE_TYPE_2D; TexDesc.Width = 1024; TexDesc.Height = 1024; TexDesc.Format = TEX_FORMAT_RGBA8_UNORM; TexDesc.Usage = USAGE_DEFAULT; TexDesc.BindFlags = BIND_SHADER_RESOURCE | BIND_RENDER_TARGET | BIND_UNORDERED_ACCESS; TexDesc.Name = "Sample 2D Texture"; m_pRenderDevice->CreateTexture( TexDesc, TextureData(), &m_pTestTex ); If native API supports multithreaded resource creation, textures and buffers can be created by multiple threads simultaneously.
      Interoperability with native API provides access to the native buffer/texture objects and also allows creating Diligent Engine objects from native handles. It allows applications seamlessly integrate native API-specific code with Diligent Engine.
      Next-generation APIs allow fine level-control over how resources are allocated. Diligent Engine does not currently expose this functionality, but it can be added by implementing IResourceAllocator interface that encapsulates specifics of resource allocation and providing this interface to CreateBuffer() or CreateTexture() methods. If null is provided, default allocator should be used.
      Initializing the Pipeline State
      As it was mentioned earlier, Diligent Engine follows next-gen APIs to configure the graphics/compute pipeline. One big Pipelines State Object (PSO) encompasses all required states (all shader stages, input layout description, depth stencil, rasterizer and blend state descriptions etc.). This approach maps directly to Direct3D12/Vulkan, but is also beneficial for older APIs as it eliminates pipeline misconfiguration errors. With many individual calls tweaking various GPU pipeline settings it is very easy to forget to set one of the states or assume the stage is already properly configured when in fact it is not. Using pipeline state object helps avoid these problems as all stages are configured at once.
      Creating Shaders
      While in earlier APIs shaders were bound separately, in the next-generation APIs as well as in Diligent Engine shaders are part of the pipeline state object. The biggest challenge when authoring shaders is that Direct3D and OpenGL/Vulkan use different shader languages (while Apple uses yet another language in their Metal API). Maintaining two versions of every shader is not an option for real applications and Diligent Engine implements shader source code converter that allows shaders authored in HLSL to be translated to GLSL. To create a shader, one needs to populate ShaderCreationAttribs structure. SourceLanguage member of this structure tells the system which language the shader is authored in:
      SHADER_SOURCE_LANGUAGE_DEFAULT - The shader source language matches the underlying graphics API: HLSL for Direct3D11/Direct3D12 mode, and GLSL for OpenGL and OpenGLES modes. SHADER_SOURCE_LANGUAGE_HLSL - The shader source is in HLSL. For OpenGL and OpenGLES modes, the source code will be converted to GLSL. SHADER_SOURCE_LANGUAGE_GLSL - The shader source is in GLSL. There is currently no GLSL to HLSL converter, so this value should only be used for OpenGL and OpenGLES modes. There are two ways to provide the shader source code. The first way is to use Source member. The second way is to provide a file path in FilePath member. Since the engine is entirely decoupled from the platform and the host file system is platform-dependent, the structure exposes pShaderSourceStreamFactory member that is intended to provide the engine access to the file system. If FilePath is provided, shader source factory must also be provided. If the shader source contains any #include directives, the source stream factory will also be used to load these files. The engine provides default implementation for every supported platform that should be sufficient in most cases. Custom implementation can be provided when needed.
      When sampling a texture in a shader, the texture sampler was traditionally specified as separate object that was bound to the pipeline at run time or set as part of the texture object itself. However, in most cases it is known beforehand what kind of sampler will be used in the shader. Next-generation APIs expose new type of sampler called static sampler that can be initialized directly in the pipeline state. Diligent Engine exposes this functionality: when creating a shader, textures can be assigned static samplers. If static sampler is assigned, it will always be used instead of the one initialized in the texture shader resource view. To initialize static samplers, prepare an array of StaticSamplerDesc structures and initialize StaticSamplers and NumStaticSamplers members. Static samplers are more efficient and it is highly recommended to use them whenever possible. On older APIs, static samplers are emulated via generic sampler objects.
      The following is an example of shader initialization:
      ShaderCreationAttribs Attrs; Attrs.Desc.Name = "MyPixelShader"; Attrs.FilePath = "MyShaderFile.fx"; Attrs.SearchDirectories = "shaders;shaders\\inc;"; Attrs.EntryPoint = "MyPixelShader"; Attrs.Desc.ShaderType = SHADER_TYPE_PIXEL; Attrs.SourceLanguage = SHADER_SOURCE_LANGUAGE_HLSL; BasicShaderSourceStreamFactory BasicSSSFactory(Attrs.SearchDirectories); Attrs.pShaderSourceStreamFactory = &BasicSSSFactory; ShaderVariableDesc ShaderVars[] = {     {"g_StaticTexture", SHADER_VARIABLE_TYPE_STATIC},     {"g_MutableTexture", SHADER_VARIABLE_TYPE_MUTABLE},     {"g_DynamicTexture", SHADER_VARIABLE_TYPE_DYNAMIC} }; Attrs.Desc.VariableDesc = ShaderVars; Attrs.Desc.NumVariables = _countof(ShaderVars); Attrs.Desc.DefaultVariableType = SHADER_VARIABLE_TYPE_STATIC; StaticSamplerDesc StaticSampler; StaticSampler.Desc.MinFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MagFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MipFilter = FILTER_TYPE_LINEAR; StaticSampler.TextureName = "g_MutableTexture"; Attrs.Desc.NumStaticSamplers = 1; Attrs.Desc.StaticSamplers = &StaticSampler; ShaderMacroHelper Macros; Macros.AddShaderMacro("USE_SHADOWS", 1); Macros.AddShaderMacro("NUM_SHADOW_SAMPLES", 4); Macros.Finalize(); Attrs.Macros = Macros; RefCntAutoPtr<IShader> pShader; m_pDevice->CreateShader( Attrs, &pShader );
      Creating the Pipeline State Object
      After all required shaders are created, the rest of the fields of the PipelineStateDesc structure provide depth-stencil, rasterizer, and blend state descriptions, the number and format of render targets, input layout format, etc. For instance, rasterizer state can be described as follows:
      PipelineStateDesc PSODesc; RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; RasterizerDesc.AntialiasedLineEnable = False; Depth-stencil and blend states are defined in a similar fashion.
      Another important thing that pipeline state object encompasses is the input layout description that defines how inputs to the vertex shader, which is the very first shader stage, should be read from the memory. Input layout may define several vertex streams that contain values of different formats and sizes:
      // Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
      // Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
      Binding Shader Resources
      Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
      Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
      Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
      PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
      Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
      m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
      As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
      This post gives more details about the resource binding model in Diligent Engine.
      Setting the Pipeline State and Committing Shader Resources
      Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
      m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
      The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
      Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
      m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
      Invoking Draw Command
      The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
      ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
      DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
      Source Code
      Full engine source code is available on GitHub and is free to use. The repository contains two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
      AntTweakBar sample is Diligent Engine’s “Hello World” example.

       
      Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

      Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

      Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

      Future Work
      The engine is under active development. It currently supports Windows desktop, Universal Windows and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
    • By michaeldodis
      I've started building a small library, that can render pie menu GUI in legacy opengl, planning to add some traditional elements of course.
      It's interface is similar to something you'd see in IMGUI. It's written in C.
      Early version of the library
      I'd really love to hear anyone's thoughts on this, any suggestions on what features you'd want to see in a library like this? 
      Thanks in advance!
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