Chapter 05

[redraw]

hey Patricio! this is a great book. I has started reading this book many times to refresh shader's concepts, but always got stucked on Chapter 05, until today that I've decided to understand it.
I've noticed you've already added this on TODO, but this is just to share my opinion.
The hard part is the color sums. Maybe splitting them, suggesting to preview the result of each one i.e.

//color = (1.0-pct)*color;

//color = pct*vec3(0.0,1.0,0.0);

color = (1.0-pct)*color + pct*vec3(0.0,1.0,0.0);

The same with smoothstep() function, although you've already offered a help tip

// the original tip
float y = smoothstep(0.2,0.5,st.x) - smoothstep(0.5,0.8,st.x);

// making the values similar to the plot() function
float y = smoothstep(0.48,0.5,st.x) - smoothstep(0.5,0.52,st.x);

great work...