Can someone help with coloring seriesWebglPoint() ?

[jodusan]

I am trying to color datapoints from d.color property but it is not working, in the console I get the error

Uncaught Error: Failed to compile shader : ERROR: 0:12: 'canStroke' : undeclared identifier
ERROR: 0:12: 'canStroke' : undeclared identifier

            Shader : 
precision mediump float;
varying float vSize;
varying vec4 vStrokeColor;
void main() {
    gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);
    float distance = length(2.0 * gl_PointCoord - 1.0);
    if (distance > 1.0) {
        discard;
        return;
    }
gl_FragColor = (canStroke * vStrokeColor) + ((1.0 - canStroke) * gl_FragColor);
gl_FragColor.a = gl_FragColor.a * (1.0 - smoothstep(vSize - 2.0, vSize, distance * vSize));
}
    at loadShader (d3fc.js:3275)
    at createProgram (d3fc.js:3250)
    at build (d3fc.js:3181)
    at draw (d3fc.js:3939)
    at point (d3fc.js:5331)
    at HTMLElement.<anonymous> (d3fc.js:8577)
    at HTMLElement.<anonymous> (on.js:27)
    at draw (d3fc.js:8116)
    at Array.forEach (<anonymous>)
    at redraw (d3fc.js:8123)
    at d3fc.js:8138

for the following js code

const pointSeries = fc
                .seriesWebglPoint()
                .crossValue(d => d.x)
                .mainValue(d => d.y)
                .size(d => 80)
                .decorate((program, data) => {
                    idx+=1;
                    
                    fcgl.webglStrokeColor().value(d=>d.color).data(data)(program);
                   
                    fc.pointAntiAlias()(program);

                    const gl = program.context();
                    gl.enable(gl.BLEND);
                    gl.blendFuncSeparate(
                        gl.SRC_ALPHA,
                        gl.ONE_MINUS_DST_ALPHA,
                        gl.ONE,
                        gl.ONE_MINUS_SRC_ALPHA
                    );
                });

Can someone help with this library? Learning curve is worse than vim, are there any good tutorials?