fwidth - return the sum of the absolute value of derivatives in x and y

       Copyright © 2011-2014 Khronos Group

[FIXME: source]                                    11/18/2024                                         FWIDTH(3G)

genTypefwidth(genTypep);genTypefwidthCoarse(genTypep);genTypefwidthFine(genTypep);

Availableonlyinthefragmentshader, these functions return the sum of the absolute derivatives in $x$
       and $y$ using local differencing for the input argument p.  fwidth is equivalent to abs(dFdx(p)) +
       abs(dFdy(p)).  fwidthCoarse is equivalent to abs(dFdxCoarse(p)) + abs(dFdyCoarse(p)).  fwidthFine is
       equivalent to abs(dFdxFine(p)) + abs(dFdyFine(p)).

       fwidth - return the sum of the absolute value of derivatives in x and y

p
           Specifies the expression of which to take the partial derivative.

dFdx()

       ┌───────────────┬───────────────────────────────────────────────────────────────────────────────────┐
       │               │        OpenGLShadingLanguageVersion                                            │
       ├───────────────┼──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┤
       │ Function      │ 1.10 │ 1.20 │ 1.30 │ 1.40 │ 1.50 │ 3.30 │ 4.00 │ 4.10 │ 4.20 │ 4.30 │ 4.40 │ 4.50 │
       │ Name          │      │      │      │      │      │      │      │      │      │      │      │      │
       ├───────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┤
       │ fwidth        │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │
       ├───────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┤
       │ fwidthCoarse, │  -   │  -   │  -   │  -   │  -   │  -   │  -   │  -   │  -   │  -   │  -   │  ✔   │
       │ fwidthFine    │      │      │      │      │      │      │      │      │      │      │      │      │
       └───────────────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┘