How to use Uniform in PixelFlow library

Hi I’m studying Processing library “PixelFlow”.
I want send Int variable to fragment shader.

How to send variable from Processing to fragmet Shader.

I’m using “Fluid_StreamLines_CustomRender” example in “Processing Example → PixelFlow → Fluid2D” (* This example have feature unlike other PixelFlow example. It load “vert shader” and “fragment shader”)

Thank you

DwPixelFlow context;
DwFluid2D fluid;
DwFluidStreamLines2D streamlines;

DwGLSLProgram customstreamlinerenderer;

public void setup() {

  String dir = "data/";
  customstreamlinerenderer = context.createShader(