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OpenGL OpenGL or Direct3D, again...

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Sorry about asking this again I know it has been discussed several times before. Anyhow, since OpenGL 3.0 turned out to be such a disappointment, does this mean it could be better to start learning Direct3D, when learning one of them from scratch? Which one is better for small home projects, like small games, and which one could be better to learn for the future if you are to work with 3D programming? Now if you think I should learn both, then the question is which one I should learn first. Cross-platform isn't really important for me right now even though it would be nice. I've been reading around at some of the older threads and it seems like a lot have recommended OpenGL so I just want to check if the opinions have changed. Thanks in advance.

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Original post by eXonius
Sorry about asking this again I know it has been discussed several times before. Anyhow, since OpenGL 3.0 turned out to be such a disappointment, does this mean it could be better to start learning Direct3D, when learning one of them from scratch?
Either will do fine.

Quote:
Which one is better for small home projects, like small games,
XNA Game Studio.

Quote:
and which one could be better to learn for the future if you are to work with 3D programming? Now if you think I should learn both, then the question is which one I should learn first.
Just pick one.

In the end, 3D programming concepts are the same, it's just 2 different APIs. It's like using printf or cout. They are different, but achieve the same thing. They both have functions that set up data to be fed to the GPU, and most of the advanced stuff is done in shaders anyways.

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You should instead decide whether you will learn using the fixed pipeline or using shaders. HLSL and GLSL look nearly the same. The libraries functions of DX/OGL you call from C/C++/"anything else" might seems different, but it ends up sending the same instructions on the video card.

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Original post by Daaark
XNA Game Studio.

Okay, I'll look into that also, though I just wonder if I'll learn as much from using this? Although my main goal is to learn as much as possible about 3D programming and the results aren't just as interesting.

Quote:
In the end, 3D programming concepts are the same, it's just 2 different APIs. It's like using printf or cout. They are different, but achieve the same thing. They both have functions that set up data to be fed to the GPU, and most of the advanced stuff is done in shaders anyways.

But cout can be smarter than printf somethimes and I just wonder if it's the same with OpenGL and Direct3D.

Quote:
You should instead decide whether you will learn using the fixed pipeline or using shaders.

Sorry but I don't really know what the difference is =/

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Look at the following list of pros(good things) about each API and then just pick one based on what you think --->

DirectX
-------
- Has many APIs to do many things such as DirectSound for sound and Direct3D for 3D programming (there are many more APIs) but is restricted to just work for Windows.

OpenGL
------
- Is cross-platform but does not focus on anything but 3D programming.

Well this isn't really all of it but...

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Original post by GuyWithNoAccent
Look at the following list of pros(good things) about each API and then just pick one based on what you think

Though this is more like a comparison between DirectX and OpenGL, for now I'm only interested about the differences of Direct3D and OpenGL (=

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One way or another you will end up doing:
1. Creating window/associating gfx adaptor to a device with this window.
2. Filling up rasterizer states.
3. Filling up buffers (vertices, indices, etc).
4. Clearing the screen.
5. Setting up WVP matrices for each objects
6. Render each objects and go back to 2 or 4.

XNA kinda just hide some step that often comes to be set in the exact same way in all projects and give you some helper functions and methods to do your work faster, but allow you to have nearly the same results than you would get with the hard way.

The fixed pipeline (DX8, DX9 and OGL without shaders). Will render the object in the "normal" looking way. You can add lights (directional/points/spots) using libraries functions. The programmable pipeline (DX10 force you to use it) need and HLSL/GLSL/CG file who is a shader program to instruct your video card on HOW to render the primitive you send it. It allow you to do neat effects, you own lighting models, etc. It is becoming a industry standard, and I guess will be there for a while, but demand more work. DX11 will be strongly based on DX10.

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I'm probably biased as I've been disgusted by the insane extension system of OpenGL ages ago (the time when 3dfx was still around). I had to get function pointers for.. uhm.. everything.. including multitexture functions.

I'd go for DirectX for several reasons:
1- you get "extra APIs" like xaudio2 or directsound
2- XNA is closer to DirectX, so if you decide to start with XNA it's probably better to continue later with DirectX. Or viceversa... who knows?
3- I never tried it but there's also SlimDX, a framework that can help you writing DirectX apps. If I'm not mistaken it's mantained by people writing here on gamedev.net.
4- DirectX SDK also includes an helper library, D3DX, which also includes useful math classes that can help you concentrate on the real thing.

On the other hand, OpenGL is simpler, probably the resulting code is cleaner, it's portable and you can learn the basic concepts of graphic programming without the need to worry about the underlying hardware architecture.

My experience is at first Direct3D seemed to me "crazy and bloated". Now I feel confortable with it and I think I'd have some problem writing code for an abstract API like OpenGL.

But again.. it's up to you, neither D3D nor OpenGL can hurt you. :)

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If this is something you want us to vote on, I'd say Direct3D. PIX and PerfHUD are invaluable for me both in debugging and performance profiling. OpenGL's got gDEBugger, but it's not free and not as functional as PIX.

I like the Direct3D API to be cleaner than OpenGL's, and you don't need to do that much validation on device capabilities. I found the OpenGL extension jungle difficult for me, especially because nVidia and AMD don't really seem to agree on common extensions to support.

I've had more success writing code with better performance on Direct3D than OpenGL, but that's just based on my experience. Certainly you can work quite fast in both.

But anyhow, even if OpenGL 3.0 turned out to be a disappointment by some, that doesn't mean that the previous version of the API all of a sudden became any worse, right? If you're really tied on which one to use, try both for a slight while to see how common tasks work with them and then choose one based on your experience.

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      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.
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