Introduction

Vertex shaders are a fundamental part of the graphics pipeline in DirectX. They process each vertex's data, transforming it from object space to screen space, and can also handle tasks such as lighting calculations and texture coordinate generation.

Key Concepts

Vertex Shader Basics:
- A vertex shader is a programmable shader stage in the graphics pipeline that handles the processing of individual vertices.
- It takes vertex attributes (like position, color, and texture coordinates) as input and outputs transformed vertex data.
HLSL (High-Level Shader Language):
- DirectX uses HLSL to write shaders. HLSL is similar to C and is designed specifically for programming shaders.
Shader Model:
- Different versions of DirectX support different shader models. Ensure your shader code is compatible with the shader model supported by your target DirectX version.

Writing a Basic Vertex Shader

Step-by-Step Guide

Define the Input and Output Structures:
- The input structure represents the data coming from the vertex buffer.
- The output structure represents the data that will be passed to the next stage in the pipeline (usually the pixel shader).

struct VS_INPUT {
    float4 Pos : POSITION; // Vertex position
    float4 Color : COLOR;  // Vertex color
};

struct VS_OUTPUT {
    float4 Pos : SV_POSITION; // Transformed position
    float4 Color : COLOR;     // Vertex color
};

Write the Vertex Shader Function:
- The vertex shader function takes the input structure and returns the output structure.
- It typically performs transformations using the world, view, and projection matrices.

VS_OUTPUT VS_Main(VS_INPUT input) {
    VS_OUTPUT output;

    // Transform the vertex position to clip space
    output.Pos = mul(input.Pos, WorldViewProjectionMatrix);

    // Pass through the vertex color
    output.Color = input.Color;

    return output;
}

Compile the Shader:
- Use the DirectX shader compiler (fxc.exe) to compile the HLSL code into a binary format that can be used by the DirectX application.

fxc /T vs_5_0 /E VS_Main /Fo VertexShader.cso VertexShader.hlsl

Practical Example

Let's create a simple vertex shader that transforms vertex positions and passes through vertex colors.

Vertex Shader Code (VertexShader.hlsl):

cbuffer ConstantBuffer : register(b0) {
    matrix WorldViewProjectionMatrix;
};

struct VS_INPUT {
    float4 Pos : POSITION;
    float4 Color : COLOR;
};

struct VS_OUTPUT {
    float4 Pos : SV_POSITION;
    float4 Color : COLOR;
};

VS_OUTPUT VS_Main(VS_INPUT input) {
    VS_OUTPUT output;
    output.Pos = mul(input.Pos, WorldViewProjectionMatrix);
    output.Color = input.Color;
    return output;
}

Compiling the Shader:

fxc /T vs_5_0 /E VS_Main /Fo VertexShader.cso VertexShader.hlsl

Integrating the Vertex Shader in a DirectX Application

Load the Compiled Shader:
- Load the compiled shader object (CSO) file into your application.

ID3D11VertexShader* vertexShader;
ID3DBlob* shaderBlob;

// Load the compiled shader
D3DReadFileToBlob(L"VertexShader.cso", &shaderBlob);

// Create the vertex shader
device->CreateVertexShader(shaderBlob->GetBufferPointer(), shaderBlob->GetBufferSize(), nullptr, &vertexShader);

Set the Vertex Shader:
- Set the vertex shader to the device context.

deviceContext->VSSetShader(vertexShader, nullptr, 0);

Define the Input Layout:
- Define the input layout that matches the input structure of the vertex shader.

D3D11_INPUT_ELEMENT_DESC layout[] = {
    { "POSITION", 0, DXGI_FORMAT_R32G32B32A32_FLOAT, 0, 0, D3D11_INPUT_PER_VERTEX_DATA, 0 },
    { "COLOR", 0, DXGI_FORMAT_R32G32B32A32_FLOAT, 0, 16, D3D11_INPUT_PER_VERTEX_DATA, 0 },
};

ID3D11InputLayout* inputLayout;
device->CreateInputLayout(layout, ARRAYSIZE(layout), shaderBlob->GetBufferPointer(), shaderBlob->GetBufferSize(), &inputLayout);

// Set the input layout
deviceContext->IASetInputLayout(inputLayout);

Practical Exercise

Exercise: Write a vertex shader that transforms vertex positions using a world matrix and passes through texture coordinates.

Define the Input and Output Structures:
- Input: Position and texture coordinates.
- Output: Transformed position and texture coordinates.
Write the Vertex Shader Function:
- Transform the vertex position using the world matrix.
- Pass through the texture coordinates.
Compile and Integrate the Shader:
- Compile the shader using fxc.
- Load and set the shader in your DirectX application.
- Define and set the input layout.

Solution:

Vertex Shader Code (VertexShader.hlsl):

cbuffer ConstantBuffer : register(b0) {
    matrix WorldMatrix;
};

struct VS_INPUT {
    float4 Pos : POSITION;
    float2 TexCoord : TEXCOORD;
};

struct VS_OUTPUT {
    float4 Pos : SV_POSITION;
    float2 TexCoord : TEXCOORD;
};

VS_OUTPUT VS_Main(VS_INPUT input) {
    VS_OUTPUT output;
    output.Pos = mul(input.Pos, WorldMatrix);
    output.TexCoord = input.TexCoord;
    return output;
}

Compiling the Shader:

fxc /T vs_5_0 /E VS_Main /Fo VertexShader.cso VertexShader.hlsl

Loading and Setting the Shader:

ID3D11VertexShader* vertexShader;
ID3DBlob* shaderBlob;

D3DReadFileToBlob(L"VertexShader.cso", &shaderBlob);
device->CreateVertexShader(shaderBlob->GetBufferPointer(), shaderBlob->GetBufferSize(), nullptr, &vertexShader);
deviceContext->VSSetShader(vertexShader, nullptr, 0);

Defining and Setting the Input Layout:

D3D11_INPUT_ELEMENT_DESC layout[] = {
    { "POSITION", 0, DXGI_FORMAT_R32G32B32A32_FLOAT, 0, 0, D3D11_INPUT_PER_VERTEX_DATA, 0 },
    { "TEXCOORD", 0, DXGI_FORMAT_R32G32_FLOAT, 0, 16, D3D11_INPUT_PER_VERTEX_DATA, 0 },
};

ID3D11InputLayout* inputLayout;
device->CreateInputLayout(layout, ARRAYSIZE(layout), shaderBlob->GetBufferPointer(), shaderBlob->GetBufferSize(), &inputLayout);
deviceContext->IASetInputLayout(inputLayout);

Conclusion

In this section, we covered the basics of writing vertex shaders in DirectX using HLSL. We learned how to define input and output structures, write the vertex shader function, compile the shader, and integrate it into a DirectX application. By practicing with the provided exercise, you should now have a solid understanding of how to create and use vertex shaders in your DirectX projects. In the next section, we will delve into writing pixel shaders, which handle the processing of individual pixels.

Writing Vertex Shaders

Introduction

Key Concepts

Writing a Basic Vertex Shader

Step-by-Step Guide

Practical Example

Integrating the Vertex Shader in a DirectX Application

Practical Exercise

Conclusion

DirectX Programming Course

Module 1: Introduction to DirectX

Module 2: Direct3D Basics

Module 3: Working with Shaders

Module 4: Advanced Rendering Techniques

Module 5: 3D Models and Animation

Module 6: Performance Optimization

Module 7: Advanced Topics

Module 8: DirectX in Practice