DirectX 教程： DirectX Tutorial - Direct3D: Drawing a Triangle

DirectX 教程： DirectX Tutorial - Direct3D: Drawing a Triangle

整个过程可以分为五步：

1. First, we tell the GPU how it is to go about rendering our geometry. 

2. Second, we create the three vertices of our triangle. 

3. Third, we store these vertices in video memory. 

4. Fourth, we tell the GPU how to read these vertices. 

5. Fifth, we finally render the triangle.

1. 要使用shader，首先要编译它

可以分为三步：

1. Loaded and compiled the two shaders 

2. Created objects for each one. 

3. Set the two objects.

void InitPipeline()
{
// load and compile the two shaders
ID3D10Blob *VS, *PS;
D3DX11CompileFromFile(L"shaders.shader", 0, 0, "VShader", "vs_4_0", 0, 0, 0, &VS, 0, 0);
D3DX11CompileFromFile(L"shaders.shader", 0, 0, "PShader", "ps_4_0", 0, 0, 0, &PS, 0, 0);

// encapsulate both shaders into shader objects
dev->CreateVertexShader(VS->GetBufferPointer(), VS->GetBufferSize(), NULL, &pVS);
dev->CreatePixelShader(PS->GetBufferPointer(), PS->GetBufferSize(), NULL, &pPS);

// set the shader objects
devcon->VSSetShader(pVS, 0, 0);
devcon->PSSetShader(pPS, 0, 0);
}

2. Vertex Buffers

In this section we learned to create a struct representing a vertex, and to create a Vertex Buffer object that handled the vertices in video memory. We built a function called InitGraphics().

这里也分为三步：

1. Created three vertices with both position and color. 

2. Created a vertex buffer object. 

3. Copied the vertices into the vertex buffer by mapping it, copying the data, and unmapping it.

// global
struct VERTEX{FLOAT X, Y, Z; D3DXCOLOR Color;}; // a struct to define a vertex
ID3D11Buffer *pVBuffer; // the vertex buffer

void InitGraphics()
{
// create a triangle using the VERTEX struct
VERTEX OurVertices[] =
{
{0.0f, 0.5f, 0.0f, D3DXCOLOR(1.0f, 0.0f, 0.0f, 1.0f)},
{0.45f, -0.5, 0.0f, D3DXCOLOR(0.0f, 1.0f, 0.0f, 1.0f)},
{-0.45f, -0.5f, 0.0f, D3DXCOLOR(0.0f, 0.0f, 1.0f, 1.0f)}
};

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

bd.Usage = D3D11_USAGE_DYNAMIC; // write access access by CPU and GPU
bd.ByteWidth = sizeof(VERTEX) * 3; // size is the VERTEX struct * 3
bd.BindFlags = D3D11_BIND_VERTEX_BUFFER; // use as a vertex buffer
bd.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE; // allow CPU to write in buffer

dev->CreateBuffer(&bd, NULL, &pVBuffer); // create the buffer

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

3. Verifying the Input Layout

In this section we covered how to coordinate the vertex buffer and the shader by using an input layout object. There was no separate function for this, but we placed the code in the InitPipeline() function, shown in bold below:

这里也分为三步：

1. Created input element descriptions for the position and the color. 

2. Created an input layout object using the shader information. 

3. Set the input layout object.

// create the input layout object
D3D11_INPUT_ELEMENT_DESC ied[] =
{
{"POSITION", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 0, D3D11_INPUT_PER_VERTEX_DATA, 0},
{"COLOR", 0, DXGI_FORMAT_R32G32B32A32_FLOAT, 0, 12, D3D11_INPUT_PER_VERTEX_DATA, 0},
};

dev->CreateInputLayout(ied, 2, VS->GetBufferPointer(), VS->GetBufferSize(), &pLayout);
devcon->IASetInputLayout(pLayout);

4. Drawing the Primitive

Finally we actually got to draw the triangle. We added a few lines of code to the RenderFrame() function.

这里的三个步骤：

1. Set which vertex buffer to use (there was only one to choose from). 

2. Set which primitive type to use. 

3. Draw the triangle.

// select which vertex buffer to display
UINT stride = sizeof(VERTEX);
UINT offset = 0;
devcon->IASetVertexBuffers(0, 1, &pVBuffer, &stride, &offset);

// select which primtive type we are using
devcon->IASetPrimitiveTopology(D3D10_PRIMITIVE_TOPOLOGY_TRIANGLELIST);

// draw the vertex buffer to the back buffer
devcon->Draw(3, 0);