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Hy. I have some little experience with opengl. But this is my queston: why the professional programmers uses directx for create games ? 1)speed? but vbo is slower than directx? 2)documentation 3)help in vs and in all community book ecc...? 4)integrated shaders vs extensions? why?

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Many reasons, the 2 main ones in my opinion being that OpenGL has been left behind constantly in terms of features and is constantly doing catch up to DX (this wasn't always the case) and the fact that ~97% of the PC game market runs Windows, so portability is really not an issue.

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There are lots of reasons, but as with any choice of technology (e.g. Windows vs Linux, Java vs C#...) you're going to have to weigh up the factors important to you and decide based on that.

In addition to Kwizatz's points, the one key advantage D3D seems to have is its ease of use. The programming model (mostly true for v9, definitely true for v10/11) is incredibly clean by comparison - quite simply, its easier to write code against. Secondly, the tools, samples, documentation, support (from MS, IHV's, community..) are generally more plentiful and complete.

For me personally, and obviously I have a bias, being able to cleanly, uniformly and concisely express my graphics application is a huge win. I've done some OpenGL coding and I found it a chaotic and messy experience - I spent as much time fighting the API/technology as I did solving my problem, which is simply not good enough in this day and age.

When there isn't a clear winner on features (yes, D3D has a slight edge but you can argue via extensions), performance and X-Platform isn't a motivator then simple ease of use and speed of development will reign king.


hth
Jack

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I've done some OpenGL coding and I found it a chaotic and messy experience

My experience is quite the opposite as I found directx messy and chaotic. I'm sure that is just because I'm used to opengl. If I started using directx I'm sure I would get used to that too.

I guess it just depends on what you are comfortable in using.

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I must agree, our proprietary Graphics Engine at work was built in DX9 and whenever I look at the source code it is a complete mess, however when I look at my own OpenGL code it looks much neater (probably bias).

Also, portability is a key factor, even if you don't think you need it now, you may need in the future, which is the problem we're facing at work where we may want to start shipping our software on Linux machines.

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Original post by AndyEsser
Also, portability is a key factor, even if you don't think you need it now, you may need in the future, which is the problem we're facing at work where we may want to start shipping our software on Linux machines.
If portability is a big factor, then you need to support multiple rendering backends, at which point OpenGL and D3D are just a few out of many.

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Original post by swiftcoder
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Original post by AndyEsser
Also, portability is a key factor, even if you don't think you need it now, you may need in the future, which is the problem we're facing at work where we may want to start shipping our software on Linux machines.
If portability is a big factor, then you need to support multiple rendering backends, at which point OpenGL and D3D are just a few out of many.


There is no reasn for having a OGL and DirectX both inside of an engine. They both do the same exact thing. and will render the same. the only thing difference is having opengl or directx rendering it. So creating a game for portability means just use opengl, and not need to have both because that basically is just adding more bloat to the engine instead of adding more functionality and a complete waste of time. But thats just my opinion.

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Original post by xZekex
There is no reasn for having a OGL and DirectX both inside of an engine. They both do the same exact thing. and will render the same. the only thing difference is having opengl or directx rendering it. So creating a game for portability means just use opengl, and not need to have both because that basically is just adding more bloat to the engine instead of adding more functionality and a complete waste of time. But thats just my opinion.


Tell that to the guys at Ogre3d [smile].

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Original post by Kwizatz
Tell that to the guys at Ogre3d [smile].


I think they already know. But isn't those just plugins? But like on professional games. who's going to really care if its has directX or Opengl based except for all the fanboys.

But iirc on OGRE, you can either support one or the other.

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Another factor is how familiar/comfortable you are with COM interfaces, the win32 libraries, and all that jazz. There are subtle differences in D3D that make it seem more win32-ish. As an example, D3D uses specific functions to return state information and does so in (often large) structs. On the other hand OpenGL gives you a few general functions that returns a single state value. If you're already comfortable with Windows programming you probably won't notice the difference too much, but if you aren't it does make a difference.

Subjectively speaking, if you are starting from scratch OpenGL definately feels easier. Just create a new C file, a couple of lines of window/GL initialization code, and you're good to go. At the minimum, you'll only need to link to your windowing library (on top of the c-runtimes of course).

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Original post by xZekex
Quote:
Original post by Kwizatz
Tell that to the guys at Ogre3d [smile].


I think they already know. But isn't those just plugins? But like on professional games. who's going to really care if its has directX or Opengl based except for all the fanboys.

But iirc on OGRE, you can either support one or the other.


Especial “professional“ (we cook with the same water too) games use an API abstraction layer as they are developed with consoles in mind. So even if you plan to release on Windows and Mac OSX it is quite common to use Direct3D for Windows and OpenGL for the Mac. The reason for this is that you have no choice on the Mac but on Windows Direct3D is the superior system. This has nothing to do with ease of development as professional developers need to be able to master any API. It’s just the quality of the environment. Direct3D drivers cause less end user trouble then OpenGL drivers as one example.

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You may also note that the PC and XBox are the only real DirectX platforms.
Every other platform (PC, Phones, PSP, PS3/PS2, Wii) has some variant of OpenGL for the graphics backend.

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Original post by Demirug
But iirc on OGRE, you can either support one or the other.


Especial “professional“ (we cook with the same water too) games use an API abstraction layer as they are developed with consoles in mind. So even if you plan to release on Windows and Mac OSX it is quite common to use Direct3D for Windows and OpenGL for the Mac. The reason for this is that you have no choice on the Mac but on Windows Direct3D is the superior system. This has nothing to do with ease of development as professional developers need to be able to master any API. It’s just the quality of the environment. Direct3D drivers cause less end user trouble then OpenGL drivers as one example.[/quote]

That is a biased statement.

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Original post by KulSeran
You may also note that the PC and XBox are the only real DirectX platforms.
Every other platform (PC, Phones, PSP, PS3/PS2, Wii) has some variant of OpenGL for the graphics backend.


The XBox Direct3D is different from the PC version and I would not call the native PS3 API a OpenGL variant. The OpenGL ES for PS3 doesn’t count as it is not useable for real games.

At the end of the day every platform its own 3D API and you are back to the need of an abstraction layer again.


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Original post by xZekex
That is a biased statement.


Biased from the professional game development point.

If OpenGL would work as well as D3D on the PC there would no need for companies like Blizzard to write an additional Direct3D renderer beside of the OpenGL one they do for the Mac.




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Original post by xZekex
Quote:
The reason for this is that you have no choice on the Mac but on Windows Direct3D is the superior system. This has nothing to do with ease of development as professional developers need to be able to master any API. It’s just the quality of the environment. Direct3D drivers cause less end user trouble then OpenGL drivers as one example.
That is a biased statement.
Biased how? I don't think anyone who has wrestled with OpenGL drivers on Windows will deny that D3D drivers are rock solid by comparison. OpenGL also has this massive problem that you can't detect what level of hardware you are running on, and end up with transparent, performance-killing software fallbacks.

Preferring one API to the other is of course a matter of bias, but it is concrete fact that D3D offers better functionality in at least a few areas, and that the drivers are more reliable.

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Microsoft have done their part to kill the PC game industry for all non Windows Operating systems. When making games for a PC, portability isn't much of an issue, so DirectX will do that fine for most. CAD programs on the other hand do need to be portable and often end up being written in OpenGL, also, graphics utility programs don't often need the extra functionality that DirectX offers over OpenGL. I've not used OpenGL much at all, I didn't find it better or worse than DirectX, but that being said I stopped using it very quickly and stuck with DirectX, better to learn one and learn it well, than learn half and half of two and have lower quality software for indy devs, hobbiests and people who enjoy graphics programming.

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As far as ease of use goes, I'm using D3D10 now for our renderer and I don't like how messy it is. Our OpenGL renderer on the other hand is very clean and straightforward.

Just my opinion, don't kill me please: the problem is that Microsoft's idea of abstraction doesn't make things any more high level or intuitive. I just find the API very far fetched and not intuitive at all.


Why are we supporting D3D in our renderer, you may ask. For Windows, of course. Like the posters above said, Direct3D is just rock solid in Windows.

My view on things:

- DirectX10 is ahead in features
- DirectX10 is superior on windows
- OpenGL is almost on par with DX10 in features but is always 1 step behind unfortunately
- OpenGL has a very simple and straightforward API without any ridiculous, farfetched abstraction.

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Original post by Brotocol
I just find the API very far fetched and not intuitive at all.


Far-fetched? I'd say that DX10 does a 1000% better job of presenting an API that resembles the way graphics hardware actually works.

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Original post by Demirug
The OpenGL ES for PS3 doesn’t count as it is not useable for real games.


I would have to disagree with that. I'm a programmer on a very real, and very big game, and most other games are using our engine in my company, and the PS3 version of the engine is made in OpenGL ES. It works fine.

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Ok, lets not have this get too heated [smile]

The "cleanliness" of code has come up a few times since I first raised it, but I think my point has been slight misunderstood compared with what I intended. Again, I state my bias and experience toward D3D first. It's the multiple path architecture that I've heard OpenGL developers discuss that I dislike. D3D9 isn't much better here but I do think D3D10 is a big step forwards with the fixed-caps design. The complexity of graphics code was (is?) too high - scaling on performance, on features, on driver stability etc... Again, from hearsay mostly but OpenGL seems to require many more paths if you want to truly utilize the hardware available.


Anyway.

What do people think of the Intel Larrabee and Tim Sweeney's latest comments? A fundamental move back to custom software rendering in the many-core world and the death of the GPU (+OpenGL/D3D style API's), or just noise...?


Jack

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Original post by BenMatlock
Quote:
Original post by Demirug
The OpenGL ES for PS3 doesn’t count as it is not useable for real games.


I would have to disagree with that. I'm a programmer on a very real, and very big game, and most other games are using our engine in my company, and the PS3 version of the engine is made in OpenGL ES. It works fine.


I don’t deny that it works. But it ate way too much performances compared to the native graphics API. If you can live with this limitation its fine.

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      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 tutorials, sample applications, asteroids performance benchmark and an example Unity project that uses Diligent Engine in native plugin.
      Atmospheric scattering sample 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, Linux, Android, MacOS, and iOS platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and Metal backend is in the plan.
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