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 WebGLRenderingContext.getExtension()
method. For more information, see also Using Extensions in the WebGL tutorial.
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
, andfwidth
.
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 argumentp
. dFdy()
-
Returns the derivative in
y
using local differencing for the input argumentp
. fwidth()
-
Returns the sum of the absolute derivative in
x
andy
using local differencing for the input argumentp
. 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
Specification |
---|
WebGL OES_standard_derivatives Khronos Ratified Extension Specification |
Browser compatibility
BCD tables only load in the browser