A Vertex Shader is a program executed on the GPU for each Vertex in a 3D model. It transforms a vertex's position, color, and texture coordinates, essentially defining where it sits in the scene and its initial properties within the Graphics Pipeline. This crucial step dictates the fundamental shape and movement of objects.
Below is a basic example of a vertex shader written in GLSL (OpenGL Shading Language), demonstrating how vertex positions are transformed from model space to clip space:
#version 330 core
layout (location = 0) in vec3 aPos; // Input vertex position
uniform mat4 model; // Model matrix
uniform mat4 view; // View matrix
uniform mat4 projection; // Projection matrix
void main()
{
// Apply model, view, and projection transformations to the vertex position
gl_Position = projection * view * model * vec4(aPos, 1.0);
}
In this example, aPos is the incoming vertex position. The model, view, and projection uniform matrices are used to transform this position through various coordinate spaces, ultimately calculating gl_Position, which determines the final position of the vertex on the screen.
Beyond just position, vertex shaders process other Vertex Attributes such as colors, Normal Vectors, and Texture Coordinates. They can also perform various per-vertex calculations, like preparing data for lighting models or implementing complex animations like Skeletal Animation.
The output of a vertex shader, often referred to as "varyings" or "interpolators," is passed to the next stage of the Graphics Pipeline, typically the Fragment Shader. These varyings are then interpolated across the surface of the primitive (e.g., triangle) before being fed to the fragment shader. This interpolation allows for smooth transitions of properties like color, texture coordinates, or lighting information across the visible surface of an object, enabling realistic rendering.
