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OpenGL Jumping over to DirectX?

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I've done some progress on learning OpenGL (models, textures, lights, point light/directional cascaded shadow maps, deferred rendering with msaa) and I'm pondering whether to make the jump over to DirectX.

 

pros:

  1. API design. As my rendering pipeline gets more complex, structuring all the various state calls into something easily understandable yet fast gets increasingly annoying, especially under some form of OOP. Is this the case for DirectX aswell? Is there a big difference?
  2. Debugging tools. AFAIK, Visual studio has built in performance and debugging tools for directx, while doing the same for opengl has proven so far to be a nightmare. There is gDEbugger (and CodeXL) but they simply don't work/crash, probably something with the window framework I'm using (GLFW 3) and it's OpenGL context switches. I work in windows under Visual studio anyway, so tight integration with debugging tools seems too good to be true.

cons:

  1. Supporting frameworks. I'm using GLEW for loading OpenGL, GLFW 3 for window management and GLM for math stuff. I have to say they are some of the best libraries I have used; my main issue with jumping to DirectX would be that I would have to get equivalent frameworks for that, and some searching has yielded basically NOTHING.
  2. Tutorials/references. The majority of what I have found seems to be OpenGL focused - DirectX guides seems kinda lackluster. Is this true?

Anyone mind chiming in with some feedback?

 

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You will get both side of the coin on this one..ultimately you will have to make the decision based on your experience with both. Without taking the plunge, you will never get a comprehensive unbiased evaluation of the two. I started out with DX 8.1 and continue throughout the years and the API has come a long way. DX used to be more forward thinking in terms of functionality, but there is parity between the 2 nowadays ( my opinion ). Currently, I'm leaning more to OpenGL because of its broad adoption across multiple devices and hardware configuration. The biggest gripe I have with DX now is the bonding of DX with OS ( need MS latest OS to use the latest DX features ). In the end they are both API to access the graphics HW for rendering/compute purposes.

For you pros and cons

Pro

1. DX is more structured that OpenGL and kudos to MS for giving that some thought. There are still different pipeline states to worry about, but again, the handling is much cleaner in DX.

2. Again, DX has the leg up on OpenGL for this one. I was a big fan of PIX ( RIP ), but there are plenty of tools out there for debugging D3D apps. The 2 that you mentioned on the OpenGL front are very good tools. I use CodeXL on a daily basis and the latest version is more stable. I also run AMD HW so I cannot comment on the stability on other HW, but it has been an invaluable tool to me. I've found 1 issue that causes it to crash/hang so avoid doing that, and so far so good.

Con:

1. As DX doesn't have an extension mechanism like OpenGL, there is not need for GLEW with DX. GLUT is a windowing utility toolkit thats tied to OpenGL so either you roll your own or use one of the may equivalent out there ex SDL. As GLM, there is nothing OpenGL inherent in math, the difference usually boils down to coordinate system convention, matrix storage layout etc..

2. The SDK documentation and samples ( installed with the SDK ) are very good and should be all you need to get your feet wet in DX.

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#L.Spiro:

 

1. I would more likely say "welcome to light side". For me, the only strong argument why I'm using OpenGL in most of my applications is one - Linux (this counts especially when you're not developing games, but software for doing various high performance computations).

 

2. Comparing bare bones applications will show you larger difference in speed, than for case of F.e. full game. But generally yes, D3D will perform better.

 

#OP & thread generally:

 

I won't even mention debugging - under OpenGL we literally had to develop our own tools from scratch (they work well, but it took us hell a lot of time to create them).

 

Dealing with AMD vs NVidia vs any other vendor (and often driver versions) under OpenGL, with some recent features, is a bloody mess (I still remember moment, where one user of my applications had troubles with 3D textures and Intel gpu, that officially supported 3D textures extension (and also OpenGL version, where it was promoted into core), but once you sampled 3D texture inside shader, you were doomed.

 

So, as for me - go right away, switch to D3D.

Edited by Vilem Otte

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I'll just add that how easy D3D is going to be for you will depend very much on how you're currently using OpenGL.  If you're used to modern OpenGL then you shouldn't have much problem translating the concepts over, but if you're still in glBegin/glEnd land you're likely to have an awful time.

 

If the latter is the case it may serve you better to do some research programs using modern OpenGL first, just to help you get a good understanding of the differences you're going to have to deal with when you port your main codebase (and to have that learning experience in a more familiar environment).

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You could buy the book '3D Game programming with DirectX11' by Frank D Luna

That's a great book; far better than any online tutorial I've seen.

With one exception: Luna uses D3DX. kunos already mentioned the DirectX toolkit libraries; these should be used instead in new code.

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Two remarks as an addition:
- PIX works fine with dx11 applications (if 32bit)
- the book uses both DirectxMath as D3DX, I think this shouldn't you from learning a lot from the book in a good readable way with doable learning curve (you can adapt other libraries when you encounter d3dx stuff while your going through the book)

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Please stay away from Direct3D!!

 

I can't speak for the API design or any of that, but Direct3D is only available for one platform. (As I understand it, the XBox version is actually a different API). If you learn Direct3D, and later decide that you want to target Linux, OS X, Android, iOS, PlayStation, et cetera, then you'll need to go back to OpenGL.

 

Right now, I guess you're only concerned about Windows. But think about 5, 10 years from now. Windows is the most popular OS because people are used to it, and developers don't bother to target other platforms. That's changing. College students are picking up OS X and finding it to be a smoother experience. Nerdy, curious developers like myself are installing Linux on an old computer or in a virtual machine, and finding out how much freedom it provides (you don't need to alter any source code, just change settings). Windows is on the decline.

 

Plus, there's the whole mobile device thing. You want into that market, and you need to know OpenGL ES.

 

If you really think that Direct3D offers enough benefits to warrant learning it, go ahead. But first, do yourself a favor: try Linux. Install it in a virtual machine, or an old computer, or set up a dual-boot on your current computer. Experiment a little. Try to find the right desktop environment for yourself. If it turns out you like GNOME, or KDE, or Unity, or one of the other thousands of desktop environments (just try five or so, not all of them) better than what you get with Windows, then it's better you find that out before you devote a bunch of time to learning an API that won't work on other platforms.

 

I used to use Windows, and I couldn't understand why anyone would bother to use anything else. But once I tried Linux, I realized that I'll never again be satisfied with an OS that forces me to pay for every new version, requires anti-virus, hogs my system resources, and won't let me customize things.

 

All I'm asking is that before you jump to a proprietary, single-platform, can't-get-the-latest-features-without-buying-a-new-OS-that-you-may-hate API, you make sure you're okay with only ever releasing games for that platform.

 

Sorry for the rant about the awesomeness of Linux. I just think that--especially with SteamOS--you need to take it into account.

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Well, sorry for offering my opinion and advice. I can see I'm not welcome here. Please continue misinterpreting my post and upvoting everyone who acts like a jerk towards me. Seriously. Knock yourself out. I'm used to being treated like crap for having a different opinion.

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You will find that throwing yourself public pity parties is shunned as much as providing heavily biased opinions as fact or even more.
Instead of shifting blame, you should consider why you were so down-voted in the first place, man up, and take steps to fix it in the future.

 

 

L. Spiro

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4) OS X is stuck in the low 4.1 OpenGL support so no modern features for you

 

My GPU (GTS 250), old as it is, can still run 95% of the triple-A games on PC, and it only supports up to OpenGL 3.3.  If you're targeting above 4.1 for "modern features", things like platform choice no longer matter because you don't really have a platform at that point unless you don't want to release for another 5 years.

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The prevailing direction is towards heavy compute based architectures which, yes, requires two rendering paths anyway ("legacy" and "compute") if you want to cover old hardware however in the AAA space at least pre-11 hardware is becoming less of a focus so your 95% will drop off pretty quickly now.

More to the point if you are working on something now then your release window is likely to be a couple of years away so saying "well, this is good enough now.." gets you no where. (A release window of less than that probably requires an existing engine, either in house or purchased, so the choice of renderer backend is already fixed either for the initial target or whatever the purchased engine supports).

Either way, Apple have shown no interest in updating OpenGL support on OSX and, despite the hardware being able to, do not support compute shaders (beyond other things) which is a major issue for many people.

Regardless pre-DX11 class hardware is yet another render path, regardless of platform or API.

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Well, sorry for offering my opinion and advice. I can see I'm not welcome here. Please continue misinterpreting my post and upvoting everyone who acts like a jerk towards me. Seriously. Knock yourself out. I'm used to being treated like crap for having a different opinion.

 

You wrote:

 

 

Right now, I guess you're only concerned about Windows

 

But yet the OP had already stated (in post #5) that Linux is currently a target platform.

 

You wrote:

 

 

If you learn Direct3D, and later decide that you want to target Linux, OS X, Android, iOS, PlayStation, et cetera, then you'll need to go back to OpenGL

 

And that's as scurillous as the infamous Wolfire blog post because most of those platforms don't actually use OpenGL (best of luck trying to port desktop GL code to GL ES).

 

Frankly, I could go on here but what's the point?  This isn't "opinion and advice", this is misinformation.  There's nothing wrong with giving opinion provided you've got facts to back it up, and in this case you don't - you are in fact just giving a sales-pitch for Linux to someone who was already targetting it anyway, and using false information to support that sales-pitch.

 

That's why you were downvoted.

Edited by mhagain

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      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.
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