A WebGL shader is a program written in the GLSL (OpenGL Shading Language) that runs on the GPU (Graphics Processing Unit) and performs calculations for rendering graphics¹. A WebGL program requires two types of shaders: a vertex shader and a fragment shader¹.

A vertex shader is a function that is called once per vertex and its job is to generate clip space coordinates, which are the final positions of the vertices on the screen². A vertex shader can also pass data to the fragment shader, such as colors, textures, or lighting information².

A fragment shader is a function that is called once per pixel (or fragment) and its job is to compute the color of the pixel based on the data passed from the vertex shader or from other sources, such as uniforms or textures². A fragment shader can also perform other effects, such as blending, fog, or post-processing².

To create a WebGL shader, you need to use the WebGLRenderingContext.createShader method, which takes a parameter indicating the type of the shader (either gl.VERTEX_SHADER or gl.FRAGMENT_SHADER) and returns a WebGLShader object¹. Then, you need to use the WebGLRenderingContext.shaderSource method to attach the GLSL source code to the shader object¹. Finally, you need to use the WebGLRenderingContext.compileShader method to compile the shader and check for any errors¹.

To use a WebGL shader, you need to attach it to a WebGL program, which is an object that links together a vertex shader and a fragment shader and allows you to set and access their inputs and outputs¹. To create a WebGL program, you need to use the WebGLRenderingContext.createProgram method, which returns a WebGLProgram object¹. Then, you need to use the WebGLRenderingContext.attachShader method to attach the shaders to the program¹. Finally, you need to use the WebGLRenderingContext.linkProgram method to link the program and check for any errors¹.

Here are some examples of creating and using WebGL shaders: