GLSL built-in function
dFdy()
Estimates the rate of change across screen-space fragment y.
Demo version: GLSL ES 1.00 / WebGL 1Demo stage: Fragment
Syntax
genType dFdy(genType p)genType means float / vec2 / vec3 / vec4; matching placeholders use the same type.
Parameters
- p
- Packed unsigned integer
Return value
An approximate screen-space y derivative for each component of p, with the same type as p.
Live example
Edit the code and the preview updates as you type.
What dFdy does
Estimates the rate of change across screen-space fragment y.
Read the preview
The derivative of sin(y*24.0) changes with row, creating horizontal color bands. Set both 24.0 values to 8.0 for wider bands with the same normalization.
Core call
abs(dFdy(sin(y*24.0)))*u_resolution.y/24.0;
This is screen-space y, not the world-space y axis of a model.
Experiment
Use sin(x*24.0) instead of sin(y*24.0) in dFdy. Since neighboring rows then receive the same input, the background becomes uniform apart from the plotted zero line.