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gavlge

DX11 how does instancing10 example works?

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 I follow what the example do and I work it out?But I still don't know why we should create two vertex buffer . One include vertex data and one include the matrix??

Also ,how can i update my matrix??

 

old:

When i read the example instancing10 in dx10;I can not understand how it works.

How to define the Vertex. Does it need to include the matrix.Why does it create two vertex buffer for instancing.

I want to do it in dx11.How should I do??

Edited by gavlge

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 Hi there! wink.png

 

How to define the Vertex. 

 

 

A vertex is what you define it as. Sounds weird, doesn't it?

 

It all depends on what kind of data you want the GPU to process, let us look at this example:

 

You want to send 3 vertices, all containing their positions and colors. You start by defining the structure, like so:

 

C++

struct MyVertex
{
    D3DXVECTOR3 Position; // or float x, y, z;
    D3DXCOLOR Color; // or float r, g, b, a;
};

Then when after creating your shader, you'll need to tell the vertex shader what data is there in each individual vertex and how the data is aligned, like so:

D3D11_INPUT_ELEMENT_DESC ied[] =
	{
		{"POSITION", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, D3D11_APPEND_ALIGNED_ELEMENT, D3D11_INPUT_PER_VERTEX_DATA, 0},
		{"COLOR", 0, DXGI_FORMAT_R32G32B32A32_FLOAT, 0, D3D11_APPEND_ALIGNED_ELEMENT, D3D11_INPUT_PER_VERTEX_DATA, 0},
	};

	if (dev->CreateInputLayout(ied, 2, VS->GetBufferPointer(), VS->GetBufferSize(), &pLayout) != S_OK)
		//Error stuff...

Now Directx operates with Buffers (Their own special format), so you'll also need to create some buffers, depending on what you wish to draw, an index buffer may also be required:

// create the vertex buffer
D3D11_BUFFER_DESC bd;
ZeroMemory(&bd, sizeof(bd));

bd.Usage = D3D11_USAGE_DYNAMIC;
bd.ByteWidth = (sizeof(D3DXVECTOR3) + sizeof(D3DXCOLOR)) * (vertexCount); // vertexCount = 3 in this case
bd.BindFlags = D3D11_BIND_VERTEX_BUFFER;
bd.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
	
dev->CreateBuffer(&bd, NULL, &pVertexBuffer);

D3D11_MAPPED_SUBRESOURCE ms;
// copy the vertices into the buffer
devcon->Map(pVertexBuffer, NULL, D3D11_MAP_WRITE_DISCARD, NULL, &ms);    // map the buffer
memcpy(ms.pData, vertexArray, sizeof(vertexArray));                 // copy the data
devcon->Unmap(pVertexBuffer, NULL);

// create the index buffer
bd.Usage = D3D11_USAGE_DYNAMIC;
bd.ByteWidth = sizeof(DWORD) * (indexCount);
bd.BindFlags = D3D11_BIND_INDEX_BUFFER;
bd.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
bd.MiscFlags = 0;

dev->CreateBuffer(&bd, NULL, &indexBuffer);

devcon->Map(indexBuffer, NULL, D3D11_MAP_WRITE_DISCARD, NULL, &ms);    // map the buffer
memcpy(ms.pData, indexArray, sizeof(indexArray));                   // copy the data
devcon->Unmap(indexBuffer, NULL);

Now your data is ready to be sent to the GPU. So when rendering your object, you should send the Vertex and the Index buffers, then draw it:

UINT stride = sizeof(D3DXVECTOR3) + sizeof(D3DXCOLOR);
UINT offset = 0;

devcon->IASetVertexBuffers(0, 1, &vertexBuffer, &stride, &offset);
devcon->IASetIndexBuffer(indexBuffer, DXGI_FORMAT_R32_UINT, 0);

devcon->DrawIndexed(indexCount, 0, 0);

PS. The parameters WILL depend on what you wish to do.

 

 

 

Does it need to include the matrix.

 

 

Again, completely depends on what you want to do. But normally you would need to send the Model (Defines the location, rotation and scalation), View (Relative camera matrix), Projection (Shape of your viewport). But these are all fancy names, you could also combine it to one matrix, and maybe call it gModelViewProjection in your shader. The vertex buffer itself doesn't need the matrix, you would need to send it to the shader as a global constant.

 

 

 

Why does it create two vertex buffer for instancing.

 

The instance buffer is a complete different buffer, that is sent along with the vertex buffer (Which might be why you said "two vertex buffers"), which can define whatever you want, and as an example, it could contain a D3DXVECTOR3 (Position), and a float (Something), if you want this data to be accessible by the shader, you'll need to change the input layout of the shader, Example:

// Add this line in the array

{"INSTANCEPOS", 0, DXGI_FORMAT_R32G32B32_FLOAT, 1, 0, D3D11_INPUT_PER_INSTANCE_DATA, 1},

// And remember to increase the number of slots (I don't remember what they are called) by 1.

An example of sending this:

unsigned int strides[2];
unsigned int offsets[2];
ID3D11Buffer* bufferPointers[2];

// Set the buffer strides.
strides[0] = sizeof(MESH_STRUCT); 
strides[1] = sizeof(D3DXVECTOR3) + sizeof(float); 

// Set the buffer offsets.
offsets[0] = 0;
offsets[1] = 0;

// Set the array of pointers to the vertex and instance buffers.
bufferPointers[0] = v;
bufferPointers[1] = b;

// Set the vertex buffer to active in the input assembler so it can be rendered.
devcon->IASetVertexBuffers(0, 2, bufferPointers, strides, offsets);
devcon->IASetIndexBuffer(i, DXGI_FORMAT_R32_UINT, 0);

PS. Why doesn't GameDev allow me to create an empty line after a code block, it becomes really messy...

 

I hope this helps you smile.png

-MIGI0027

Edited by Migi0027

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Please don't edit your first question to ask a new question and give a response of what I wrote, it confuses me, instead leave a new post down here.

 

I really recommend this site:

 

http://www.directxtutorial.com/LessonList.aspx?listid=11

 

I know some people say that it isn't top quality and/or misses some fundamental parts, but it was the site which got me started with Directx.

 

-MIGI0027

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