OES_standard_derivatives extension

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 getExtension() method. For more information, see also Using Extensions in the WebGL tutorial.

[!NOTE] This extension is only available to WebGL1 contexts. In WebGL2, the functionality of this extension is available on the WebGL2 context by default. In WebGL 2, the constant is available as gl.FRAGMENT_SHADER_DERIVATIVE_HINT and it requires GLSL #version 300 es.

Constants

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

• ext.FRAGMENT_SHADER_DERIVATIVE_HINT_OES
  • : A GLenum indicating the accuracy of the derivative calculation for the GLSL built-in functions: dFdx, dFdy, and fwidth.

GLSL built-in functions

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

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

• dFdx()
  • : Returns the derivative in x using local differencing for the input argument p.
• dFdy()
  • : Returns the derivative in y using local differencing for the input argument p.
• fwidth()
  • : Returns the sum of the absolute derivative in x and y using local differencing for the input argument p. That is, abs(dFdx(p)) + abs(dFdy(p)).

dFdx() and dFdy() are commonly used to estimate the filter width used to anti-alias procedural textures.

Examples

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>

Specifications

Browser compatibility

See also

• getExtension()
• EXT_shader_texture_lod