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DX11 [DX11] - Compute Shader questions.

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Hey! im doing some Compute shaderstuff and got lost and since the lack of (in my opinion) good tutorials, i need some answers.

Q1 :

//C++
csDesc.BindFlags = D3D11_BIND_UNORDERED_ACCESS | D3D11_BIND_SHADER_RESOURCE;
csDesc.CPUAccessFlags = 0;
csDesc.MiscFlags = D3D11_RESOURCE_MISC_BUFFER_STRUCTURED;
csDesc.StructureByteStride = sizeof(data);
csDesc.ByteWidth = sizeof(data) * t_Size_X * t_Size_Y;
csDesc.Usage = D3D11_USAGE_DEFAULT;



this code aboves creates a buffer, and that is starightforward.
But the only parameter value i find odd is the ByteWidth.

Data in this case is an float4.
why do i do the sizeof(data)*size_X*size_Y?
To specifi that i whant to make an 2d array of floats?

Q2 :
In the hlsl code, where should i put the eoutput?

Q3 :
(this question is related to question one)
If i specify to make a 2d array out of floats.
How do i know in wich element i am calculating right now?
my toughts where that the SV_GroupThreadID semantic would have the eye for that.

Q4 :
How do i read the output values in my cpp code?
(is this possible?)


If you have any good tutorials or any good booktips, let me know!
And thanks for all help.


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I'll try to give some insight on these topics:

Q1: The ByteWidth is the size of the buffer in bytes. So you say the size of the element, multiplied by the number of elements.

Q2: The output from the compute shader is done through an unordered access view (UAV). This is a big difference from the other stages - the compute shader handles its own output, allowing for fairly flexible setups.

Q3: That's right, but only if you have only a single thread group. If you are using a 2D grid represented by the 1D buffer, then you need to create a 1D index to use from your 2D ID information. If you have more than one group, then use the dispatch thread ID. If you only have one group, you can use either the dispatch or group thread ID's. The Water Simulation demo in my engine (link is in my signature) has just such a setup to hold the state of the water if you are looking for an example.

Q4: You need to create a staging buffer (a secondary buffer with staging usage) then copy the results to it, and then map that buffer and read the data out on the CPU side.

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Q1 :
so there is no need to have a sizeof*x*y.
i could just go and create a array instead and size that?
Or i could make a real nig struct with diffrent kinds (if i would only whant to make one caluclation) of data types?

What i understood it from the tutorial (and hes purpose), was that he wanted to created a buffer big enough for a 16x16 float4 array, so he later could use it as an image.
and since images make most sence in 2d, he used the sizeX*sizeY.

Q2 :

That i know, to specify the question more, where do i output it in the hlsl code?

RWStructuredBuffer<BufferStruct> g_OutBuff;
[numthreads( 4, 4, 1 )]
void mainCS( uint3 threadIDInGroup : SV_GroupThreadID, uint3 groupID : SV_GroupID )
{
float4 color = threadIDInGroup.x * threadIDInGroup.y * threadIDInGroup.z;
g_OutBuff[ 0 ].color = color;
}



Here i am send the data to the g_OutBuff[0].color?
I just took this plain and simpel from the tutorial and i think i understand it so that the gOutbuff is the pixelshaders answer for "return color;".

Q3 :
Well, that was close to what i tought.
So the buffer is never ever a "2d buffer" it is allways a 1d buffer?
and there for i have to divide the size of (xNum*xElemntSize)/(yNum*yElementSize)?
and that index i allso use for the g_OutBuff[index]? instead of putting 0 there?
And i will have a look on your stuff!

Q4 :
Ah, so when i mapp the buffer, instead of writing to it, just read from it.
That make sense!

Thanks alot Jason!

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Quote:
Original post by Tordin
Q2 :

That i know, to specify the question more, where do i output it in the hlsl code?
*** Source Snippet Removed ***

Here i am send the data to the g_OutBuff[0].color?
I just took this plain and simpel from the tutorial and i think i understand it so that the gOutbuff is the pixelshaders answer for "return color;".


Compute shaders don't really "return" anything; you declare one or more ouput buffers and you can write to them at any point during the execution of the shader, much like a normal C/C++ function writing to an array.

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phantom : Precisly, i understand that, and that is why i wrote "Return color". it dose the similar thing in another way just.

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Quote:
Original post by Tordin
Q1 :
so there is no need to have a sizeof*x*y.
i could just go and create a array instead and size that?
Or i could make a real nig struct with diffrent kinds (if i would only whant to make one caluclation) of data types?

What i understood it from the tutorial (and hes purpose), was that he wanted to created a buffer big enough for a 16x16 float4 array, so he later could use it as an image.
and since images make most sence in 2d, he used the sizeX*sizeY.

The sizeof*x*y is just to select enough memory to hold his 2D grid of points (I assume). Buffers are always 1D, while texture resources can be 1D, 2D, or 3D. Technically you can use a Texture2D to achieve the same result, so you just need to choose the resource type that allows for the most coherent memory access with a minimal amount of address calculations.
Quote:
Original post by Tordin
Q2 :

That i know, to specify the question more, where do i output it in the hlsl code?
*** Source Snippet Removed ***

Here i am send the data to the g_OutBuff[0].color?
I just took this plain and simpel from the tutorial and i think i understand it so that the gOutbuff is the pixelshaders answer for "return color;".

This depends on the type of 'resource object' you declare in your shader, which is the interface that you work with your resource through. When you bind a resource to the compute shader through either an SRV or a UAV, on the HLSL side you must declare an object that represents it. In your case, it is a RWStructuredBuffer<BufferStruct> (which is a clever name by the way :P ). This object allows for array like access to its contents (which are again only 1D). Other objects like an append/consume buffer have different access mechanisms.
Quote:
Original post by Tordin
Q3 :
Well, that was close to what i tought.
So the buffer is never ever a "2d buffer" it is allways a 1d buffer?
and there for i have to divide the size of (xNum*xElemntSize)/(yNum*yElementSize)?
and that index i allso use for the g_OutBuff[index]? instead of putting 0 there?
And i will have a look on your stuff!

I don't clearly understand the equation you show above, but in general if you have the 2D location in the grid that you want, you can find the index by using the following: index = location.x + size_x * location.y You are just making a linear index out of a 2D one like you would in the same situation in C++.
Quote:
Original post by Tordin
Q4 :
Ah, so when i mapp the buffer, instead of writing to it, just read from it.
That make sense!

Thanks alot Jason!

Keep in mind that you have to provide the correct arguments to the map function in order to be able to read the data, and that it must be created with the proper access flags as well!

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Q1 :
Yes well now i understand it perfect :)

Q2 :
Hmm alright... This was a bit confusing thoe so i think i have to read up on that subject!
(and i couldent find a way to see your water shader demo)

Q3 :
haha, no that equation was wrong, but what i was trying to say is what you just said :P

Q4 :
What bindflags should i use for the mapp buffer?
I just started to test this with the following code, but since i dident know wich bindflag to use i just used the "Shader_Resource" one.
like this

cbDesc.Usage = D3D11_USAGE_STAGING;
cbDesc.BindFlags = D3D11_BIND_SHADER_RESOURCE;
cbDesc.CPUAccessFlags = D3D11_CPU_ACCESS_READ;


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Since you won't be binding the staging resource to the pipeline at all, it doesn't matter what bind flag you use (and you should probably set it to 0). The key is in the ID3D11DeviceContext::Map() function - you need to pass the D3D11_MAP_READ flag for reading the contents of the buffer.

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I managed to create the buffer and all that, but that brings me to another question, how do i know what in the buffer i am looking for?

this is my shader so far

struct BufferStruct
{
float4 color;
};
RWStructuredBuffer<BufferStruct> g_OutBuff;
[numthreads( 4, 1, 1 )]
void mainCS( uint3 threadID : SV_GroupThreadID, uint3 groupID : SV_GroupID )
{
g_OutBuff[threadID.x].color = float4(10+10,0.0f,0.0f,0.0f);
}


im just trying to experiment with one calculation of a float4, so i specifed the numthreads to x4,y1,z1 since i only what 4 threads in xdim and none more since there is only one float. ( i think i got that correct )

Now i am outputting the value to the G_OutBuffer[at the threads x value];

And in my map function i am just pointing in the buffer i converted from the mapped resource.
like this

m_pD3DContex->CopyResource(MapBuffer,m_pComputeShaderBuffer);

hr = m_pD3DContex->Map(MapBuffer,0,D3D11_MAP_READ,0,&cbMapped);
if(ChekReturnError(hr))
return false;
Buffer = (MORN_VARIABLE_BUFFER_COMPUTE*)cbMapped.pData;
m_pD3DContex->Unmap(MapBuffer,0);



in my head this is correct, but my values are not.
please point me in the right direction for this.

cheers!

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I just did slove it, i did managed to create the destination buffer a bit to small :)

! Thanks alot guys for all the help, this has been very intressting and learning in all ways :)



(this post might even gets sticked becuase it contain lost of questions about ComputeShaders)

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      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.
    • By trojanfoe
      I hope this is the right place to ask questions about DirectXTK which aren't really about graphics, if not please let me know a better place.
      Can anyone tell me why I cannot do this:
      DirectX::SimpleMath::Rectangle rectangle = {...}; RECT rect = rectangle; or
      RECT rect = static_cast<RECT>(rectangle); or
      const RECT rect(m_textureRect); despite Rectangle having the following operator RECT:
      operator RECT() { RECT rct; rct.left = x; rct.top = y; rct.right = (x + width); rct.bottom = (y + height); return rct; } VS2017 tells me:
      error C2440: 'initializing': cannot convert from 'const DirectX::SimpleMath::Rectangle' to 'const RECT' Thanks in advance
    • By isu diss
      I'm trying to duplicate vertices using std::map to be used in a vertex buffer. I don't get the correct index buffer(myInds) or vertex buffer(myVerts). I can get the index array from FBX but it differs from what I get in the following std::map code. Any help is much appreciated.
      struct FBXVTX { XMFLOAT3 Position; XMFLOAT2 TextureCoord; XMFLOAT3 Normal; }; std::map< FBXVTX, int > myVertsMap; std::vector<FBXVTX> myVerts; std::vector<int> myInds; HRESULT FBXLoader::Open(HWND hWnd, char* Filename, bool UsePositionOnly) { HRESULT hr = S_OK; if (FBXM) { FBXIOS = FbxIOSettings::Create(FBXM, IOSROOT); FBXM->SetIOSettings(FBXIOS); FBXI = FbxImporter::Create(FBXM, ""); if (!(FBXI->Initialize(Filename, -1, FBXIOS))) { hr = E_FAIL; MessageBox(hWnd, (wchar_t*)FBXI->GetStatus().GetErrorString(), TEXT("ALM"), MB_OK); } FBXS = FbxScene::Create(FBXM, "REALMS"); if (!FBXS) { hr = E_FAIL; MessageBox(hWnd, TEXT("Failed to create the scene"), TEXT("ALM"), MB_OK); } if (!(FBXI->Import(FBXS))) { hr = E_FAIL; MessageBox(hWnd, TEXT("Failed to import fbx file content into the scene"), TEXT("ALM"), MB_OK); } FbxAxisSystem OurAxisSystem = FbxAxisSystem::DirectX; FbxAxisSystem SceneAxisSystem = FBXS->GetGlobalSettings().GetAxisSystem(); if(SceneAxisSystem != OurAxisSystem) { FbxAxisSystem::DirectX.ConvertScene(FBXS); } FbxSystemUnit SceneSystemUnit = FBXS->GetGlobalSettings().GetSystemUnit(); if( SceneSystemUnit.GetScaleFactor() != 1.0 ) { FbxSystemUnit::cm.ConvertScene( FBXS ); } if (FBXI) FBXI->Destroy(); FbxNode* MainNode = FBXS->GetRootNode(); int NumKids = MainNode->GetChildCount(); FbxNode* ChildNode = NULL; for (int i=0; i<NumKids; i++) { ChildNode = MainNode->GetChild(i); FbxNodeAttribute* NodeAttribute = ChildNode->GetNodeAttribute(); if (NodeAttribute->GetAttributeType() == FbxNodeAttribute::eMesh) { FbxMesh* Mesh = ChildNode->GetMesh(); if (UsePositionOnly) { NumVertices = Mesh->GetControlPointsCount();//number of vertices MyV = new XMFLOAT3[NumVertices]; for (DWORD j = 0; j < NumVertices; j++) { FbxVector4 Vertex = Mesh->GetControlPointAt(j);//Gets the control point at the specified index. MyV[j] = XMFLOAT3((float)Vertex.mData[0], (float)Vertex.mData[1], (float)Vertex.mData[2]); } NumIndices = Mesh->GetPolygonVertexCount();//number of indices MyI = (DWORD*)Mesh->GetPolygonVertices();//index array } else { FbxLayerElementArrayTemplate<FbxVector2>* uvVertices = NULL; Mesh->GetTextureUV(&uvVertices); int idx = 0; for (int i = 0; i < Mesh->GetPolygonCount(); i++)//polygon(=mostly triangle) count { for (int j = 0; j < Mesh->GetPolygonSize(i); j++)//retrieves number of vertices in a polygon { FBXVTX myVert; int p_index = 3*i+j; int t_index = Mesh->GetTextureUVIndex(i, j); FbxVector4 Vertex = Mesh->GetControlPointAt(p_index);//Gets the control point at the specified index. myVert.Position = XMFLOAT3((float)Vertex.mData[0], (float)Vertex.mData[1], (float)Vertex.mData[2]); FbxVector4 Normal; Mesh->GetPolygonVertexNormal(i, j, Normal); myVert.Normal = XMFLOAT3((float)Normal.mData[0], (float)Normal.mData[1], (float)Normal.mData[2]); FbxVector2 uv = uvVertices->GetAt(t_index); myVert.TextureCoord = XMFLOAT2((float)uv.mData[0], (float)uv.mData[1]); if ( myVertsMap.find( myVert ) != myVertsMap.end() ) myInds.push_back( myVertsMap[ myVert ]); else { myVertsMap.insert( std::pair<FBXVTX, int> (myVert, idx ) ); myVerts.push_back(myVert); myInds.push_back(idx); idx++; } } } } } } } else { hr = E_FAIL; MessageBox(hWnd, TEXT("Failed to create the FBX Manager"), TEXT("ALM"), MB_OK); } return hr; } bool operator < ( const FBXVTX &lValue, const FBXVTX &rValue) { if (lValue.Position.x != rValue.Position.x) return(lValue.Position.x < rValue.Position.x); if (lValue.Position.y != rValue.Position.y) return(lValue.Position.y < rValue.Position.y); if (lValue.Position.z != rValue.Position.z) return(lValue.Position.z < rValue.Position.z); if (lValue.TextureCoord.x != rValue.TextureCoord.x) return(lValue.TextureCoord.x < rValue.TextureCoord.x); if (lValue.TextureCoord.y != rValue.TextureCoord.y) return(lValue.TextureCoord.y < rValue.TextureCoord.y); if (lValue.Normal.x != rValue.Normal.x) return(lValue.Normal.x < rValue.Normal.x); if (lValue.Normal.y != rValue.Normal.y) return(lValue.Normal.y < rValue.Normal.y); return(lValue.Normal.z < rValue.Normal.z); }  
    • By Karol Plewa
      Hi, 
       
      I am working on a project where I'm trying to use Forward Plus Rendering on point lights. I have a simple reflective scene with many point lights moving around it. I am using effects file (.fx) to keep my shaders in one place. I am having a problem with Compute Shader code. I cannot get it to work properly and calculate the tiles and lighting properly. 
       
      Is there anyone that is wishing to help me set up my compute shader?
      Thank you in advance for any replies and interest!
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