Shader Combinations
Create a function for both of your shaders and return the output then as MrEliptik stated multiply the results
Example
vec3 radial_gradient(){
return output
}
vec3 voronoi(){
#your code here
return output
}
void fragment(){
COLOR = voronoi() * radial_gradient()
}
Tips
The output var is what you would normally have in your fragment function as ABEDO = output
or COLOR = output
If multiply gives you unusual results try also multiplying by a fraction or adding instead
If you're familiar with Visual Shaders this actually gets done for you automatically and the added bonus of seeing it live to make tweaks