Vertex Shader
A vertex shader is a program that runs on the graphics processing unit (GPU) and is responsible for transforming individual vertices. It takes vertex data as input, performs mathematical operations such as translation, rotation, scaling, and projection, and outputs transformed vertex data, typically including position, color, and texture coordinates. This process is a fundamental part of the graphics pipeline, enabling the rendering of 3D scenes.
Purpose and Functionality
The primary roles of a vertex shader include:
- Vertex Transformation: Applying world, view, and projection matrix transformations to bring vertices from object space to clip space.
- Lighting Calculations: Performing per-vertex lighting computations based on vertex normals and light sources.
- Texture Coordinate Generation: Manipulating or generating texture coordinates for texturing.
- Color Manipulation: Modifying vertex colors based on various factors.
- Data Streaming: Passing data to subsequent stages of the graphics pipeline (e.g., pixel shaders).
Input and Output
Vertex shaders typically receive input data that includes:
- Vertex position (e.g.,
float3,float4) - Vertex normal (e.g.,
float3) - Texture coordinates (e.g.,
float2,float3) - Vertex color (e.g.,
float4) - Other custom attributes
The essential output from a vertex shader is the transformed vertex position in clip space. Other outputs, often referred to as "varyings" or "interpolators," are passed to the next stage (typically the rasterizer or geometry shader) for interpolation across primitives. These can include:
- Transformed position
- World-space position
- Normals
- Texture coordinates
- Vertex colors
Shader Languages
Vertex shaders are commonly written using high-level shading languages such as:
- HLSL (High-Level Shading Language): The primary shading language for DirectX.
- GLSL (OpenGL Shading Language): Used with OpenGL and Vulkan.
These languages are then compiled into GPU-specific machine code.
Example (HLSL)
Here's a simplified example of a vertex shader in HLSL:
struct VertexInput {
float4 position : POSITION;
float4 color : COLOR;
};
struct VertexOutput {
float4 position : SV_POSITION;
float4 color : COLOR;
};
cbuffer MyConstants {
float4x4 worldViewProjection;
};
VertexOutput main(VertexInput input) {
VertexOutput output;
output.position = mul(input.position, worldViewProjection);
output.color = input.color;
return output;
}