The OES_standard_derivatives extension is part of the WebGL API and adds the GLSL derivative functions dFdx, dFdy, and fwidth.

WebGL extensions are available using the WebGLRenderingContext.getExtension() method. For more information, see also Using Extensions in the WebGL tutorial.

This extension exposes one new constant, which can be used in the hint() and getParameter() methods.

ext.FRAGMENT_SHADER_DERIVATIVE_HINT_OES

A WebGL_API.Types indicating the accuracy of the derivative calculation for the GLSL built-in functions: dFdx, dFdy, and fwidth.

The following new functions can be used in GLSL shader code, if this extension is enabled:

genType dFdx(genType)
genType dFdy(genType)
genType fwidth(genType)

Enabling the extensions:

gl.getExtension("OES_standard_derivatives");
gl.getExtension("EXT_shader_texture_lod");

Shader code that avoids artifacts when wrapping texture coordinates:

<script type="x-shader/x-fragment">
  #extension GL_EXT_shader_texture_lod : enable
  #extension GL_OES_standard_derivatives : enable

  uniform sampler2D myTexture;
  varying vec2 texcoord;

  void main(){
    gl_FragColor = texture2DGradEXT(myTexture, mod(texcoord, vec2(0.1, 0.5)),
                                    dFdx(texcoord), dFdy(texcoord));
  }
</script>

• WebGLRenderingContext.getExtension()
• EXT_shader_texture_lod