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DX11 C++ DX API, help me get it?

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Ok so i'm coming from a .net background (multiple years of professional development).

I'm checking out microsoft DX11 samples and i just don't get it, am i missing something obvious & there's actually beauty there i'm not seeing? Or is this actually just flat ugly hard code for no reason? Is it legacy or are you actually supposed to write & consume APIs this way?

(just to be clear, this is half rant, half question, i'd be more than happy to learn my rant is unfounded & have this transition from a rant to an answered question, also i'm not saying i'm having a hard time, just to be clear i understand the sample perfectly fine, i just find it painstakingly hard for no reason).

 

Shed some light on all this for me

1) Why the hell is this so damn long & hard? I expected getting a DX11 window up & running (and rendering) with nothing inside to be a 10liner or so, maybe 20 tops, but not 250 like in the sample!

2) Why the typedefs? Seems to be adding confusion for no reason especially on simple types, am i missing something or is this just useless? typedef float               FLOAT

3) Why no constructors? Objects are just declared and initialized element by element, meaning you remove 1 line you don't get a default, you don't even get an exception, you get a nice access violation!

4) Why all the if(failed(bla)) ? Why isn't code throwing?

5) Probably the same as 3 but, why no sensible default values for everything? Declaring any directX object seems to be a full time job & a 10 liner!

6) Why is everything taking a pointer? I get the point for large (or medium) objects but why for example does something like the feature level, which isn't a large object nor an array, and that you're likely to be using once (or hell, maybe twice!) in your whole application get passed by pointer? I'm new at C++ but unless i get it wrong it means you must create a (local or global) variable, assign a value to it, and pass a pointer to it, if it was by reference you could just pass in D3D_FEATURE_LEVEL_11_0 for example

7) Typedef question again, it's confusing enough for float => FLOAT, but hell LPVOID*, i can't believe people starting with C++ make it through this!

8) __uuidof, so you even need custom keywords to get a simple directX sample app going on???

 

I'm not trying to bash C++ here, the only things i can't bare in it are header files and compilation speed, but i just don't get that API design, is it flaws in the API or in the sample? Or am i just getting it wrong? Because if this is the right way to do it this sounds just horrible to me, 250 lines to do nothing, 3X that much for a rotating cube (out of which only 60 lines are rendering, and about 300 setting up the device . . . ). I just don't get it! Hell SharpDX didn't feel that way at all.

 

I'm waiting, please enlighten me!

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Allow me to pick off part of #6:

 

D3D11CreateDeviceAndSwapChain has two parameters that accept pointers to D3D_FEATURE_LEVEL. The first one is a pointer because it is actually looking for an array of D3D_FEATURE_LEVEL (and the parameter following that one is the number of elements in the array). The second one is a pointer because it is an output parameter to where the feature level that was actually selected can be stored.

 

http://msdn.microsoft.com/en-us/library/windows/desktop/ff476083(v=vs.85).aspx

 

[EDIT]

Also, I expect that a lot of the reasons for the API being structured how it is are due to http://en.wikipedia.org/wiki/Component_Object_Model

Edited by jrh2365

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1) Short version, modern languages and frameworks tend to do a lot of the work for you. This is the raw api.

2) typedef float FLOAT, might become typedef double FLOAT in the future, dont need to change as much later you can redefine FLOAT.

3) Windows has a long history with C, it tends to be the main focus when extending the windows apis, C has no constructors

4) see 3

5) see 3

6) see 3

7) see 3

8) see 3

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That's why I keep my distance from C++! Even in C# you need to write a lot of code just to set up a device. It is certainly nicer to look at, less * and & :D But once you begin writing your engine you can abstract away all that. In my own engine everything boils down to a call to DeviceManager.Initialize where I pass my own settings structure... and that's that.

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As the others have already mentioned, you are comparing two different things.  C++ has direct access to the D3D API, and hence has to do the heavy lifting to get anything going.  But SharpDX is actually just a library that sits between you and the API to make things easier.  Most people don't start from scratch in C++ either - for example, in the Hieroglyph 3 application framework, you just inherit from a class and your window setup, device setup, and all the other goodies are done without any additional code.

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One thing not a lot of people realize is that most of the Windows API samples are written so that non-C and C++ programmers will understand them. For instance, when initializing structs the API samples will use ZeroMemory() despite the fact that = {} will do the same thing. However, non-C or C++ programmers won't necessarily understand that, so the explicit ZeroMemory() call is used instead.

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Ok so as i expected most of it is to be blamed on legacy or COM, actually makes me quite happy to hear that.

 

Is there any library on the C++ side that does the same as SharpDX for .net? (keep the same low level API access, but wrap it in namespaced classes with default constructors etc, something that would feel more "modern C++ish" without being an engine but that would be a good base for starting one without doing my own wrappers on everything?)

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4) Why all the if(failed(bla)) ? Why isn't code throwing? 

 

 NEVER use exceptions in C++! I love HRESULT error codes
 

6) Why is everything taking a pointer? I get the point for large (or medium) objects but why for example does something like the feature level, which isn't a large object nor an array, and that you're likely to be using once (or hell, maybe twice!) in your whole application get passed by pointer? I'm new at C++ but unless i get it wrong it means you must create a (local or global) variable, assign a value to it, and pass a pointer to it, if it was by reference you could just pass in D3D_FEATURE_LEVEL_11_0 for example

 

 Use CComPtr(atlbase.h) if you dont like pointers...

 

LPVOID

 

well.... i really dont care about PVOID LPVOID FLOAT ect...


D3D is designed for performance and user-control.. If you dont like that then you can use something like irrlicht/ogre/panda/whatever

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4) Why all the if(failed(bla)) ? Why isn't code throwing? 

 

 NEVER use exceptions in C++! I love HRESULT error codes
 

6) Why is everything taking a pointer? I get the point for large (or medium) objects but why for example does something like the feature level, which isn't a large object nor an array, and that you're likely to be using once (or hell, maybe twice!) in your whole application get passed by pointer? I'm new at C++ but unless i get it wrong it means you must create a (local or global) variable, assign a value to it, and pass a pointer to it, if it was by reference you could just pass in D3D_FEATURE_LEVEL_11_0 for example

 

 Use CComPtr(atlbase.h) if you dont like pointers...

 

LPVOID

 

well.... i really dont care about PVOID LPVOID FLOAT ect...


D3D is designed for performance and user-control.. If you dont like that then you can use something like irrlicht/ogre/panda/whatever

 

None of this relates to performance at all, unless you consider "setting up directx" a performance critical part of any application where it's important to saveup nanoseconds in object instantiation and saving 4 bytes copies here & there? Performance is no reason here (i could get it if it was in per frame actions, but just not here), nor does it relate to user control at all. Anyway i already had my answers earlier on this thread, it's just com limitations & legacy code.

 

So now just looking for a thin wrapper around it, NOT an engine, something like a directX for actual C++ and not com/C.

Anyone could recommand such a thing? Something very thin where i could still refer to DX documentation, but just use it in a more "modern C++" way, C++11 is fine (within visual studio 2013's limitations)

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So now just looking for a thin wrapper around it, NOT an engine, something like a directX for actual C++ and not com/C.

Anyone could recommand such a thing? Something very thin where i could still refer to DX documentation, but just use it in a more "modern C++" way, C++11 is fine (within visual studio 2013's limitations)

 

 

Take a look at "A Modern C++ Library for DirectX Programming" by Kenny Kerr:

http://msdn.microsoft.com/en-us/magazine/dn201741.aspx

http://dx.codeplex.com/

 

Seems to be exactly what you're describing:

I didn’t want to produce yet another heavy wrapper around DirectX. Instead, I decided to leverage C++11 to produce a simpler API for DirectX without imposing any space and time overheard to the core DirectX API.

 

If you'd like to have something on a yet higher level, check out SFML (Simple and Fast Multimedia Library):

http://www.sfml-dev.org/

Edited by Matt-D

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None of this relates to performance at all

 

Exceptions have a noticeable performance impact, which is one of the reasons many game projects at least do not use them. From that perspective it makes sense from an API point of view to not rely on them (in addition to C legacy)

 

I don't know of any wrappers like that you are describing, but you could take just the API abstraction layer of any openly available engine and start with that instead of interfacing directly with d3d if you really wanted to. It would be better to use it natively if you want to learn how it works though I think.
 

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None of this relates to performance at all, unless you consider "setting up directx" a performance critical part of any application where it's important to saveup nanoseconds in object instantiation and saving 4 bytes copies here & there? Performance is no reason here (i could get it if it was in per frame actions, but just not here), nor does it relate to user control at all. Anyway i already had my answers earlier on this thread, it's just com limitations & legacy code.

 

Setting up DirectX can be a "performance critical" part. Just depends whom you work for. 

Some places have STRICT requirements on startup times.

Last company i worked at our game window had to be up and displaying something in under three seconds or all hell broke loose.

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Jason Z's (http://hieroglyph3.codeplex.com/) has really good wrappers!

 

Like he said, Hieroglyph 3 is a layered framework that can be used at a high level or at a lower level.  At the very least, you can take a look at it and see if it does what you want.  There are lots of sample applications, ranging from very simple (just clearing the window to a different color) all the way up to volume rendering, Kinect integration, and deferred/light pre-pass rendering.

 

If you want something very light, you can grab pieces of the framework and use them as you see fit - it is licensed under MIT, so it is quite liberal for you to use.

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      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 kan123
      Hello,
      DX9Ex. I have the problem with driver stability in time of serial renderings, which i try to use for image processing in memory with fragment shaders. For big bitmaps the video driver sometimes becomes unstable ("Display driver stopped responding and has recovered") and, for instance, if the media player runs video in background, it sometimes freezes and distorts. I tried to use next methods of IDirect3DDevice9Ex:
      SetGPUThreadPriority(-7);
      WaitForVBlank(0);
      EvictManagedResources();
      with purpose to give some time for GPU between scenes, but it seems to be has not notable effect in this case. I don't want to reinitilialize subsystem for every step to avoid performance loss.
      So, my question is next: does some common practice exists to avoid overloading of GPU by running tasks? Many thanks in advance.
       
    • By AxeGuywithanAxe
      I wanted to see how others are currently handling descriptor heap updates and management.
      I've read a few articles and there tends to be three major strategies :
      1 ) You split up descriptor heaps per shader stage ( i.e one for vertex shader , pixel , hull, etc)
      2) You have one descriptor heap for an entire pipeline
      3) You split up descriptor heaps for update each update frequency (i.e EResourceSet_PerInstance , EResourceSet_PerPass , EResourceSet_PerMaterial, etc)
      The benefits of the first two approaches is that it makes it easier to port current code, and descriptor / resource descriptor management and updating tends to be easier to manage, but it seems to be not as efficient.
      The benefits of the third approach seems to be that it's the most efficient because you only manage and update objects when they change.
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