uv holds the screen-space coordinates adjusted for the aspect ratio.
Visualize this by setting the color to the euclidian distance to the origin. Use length(). You can save the distance in the float called
d.
Having just one color can be a bit boring, so let's use a palette. Send the calculated distance to the
palette() function and use the return value as color.
Now let's transform d to be something more that just the euclidian distance. Make sure to do
the transformations after calculating the palette color.
Create concentric sine waves with: d = sin(d * 8.0 - time) / 8.0;
They are a little dark so boost the values: d = 0.02 / d;
Negative values don't help us very much so we can use them to double the frequency:
d = abs(d);
Let's add some latitudal and longitudal dependencies as well. Introduce two new variables:
float s = sin(uv.x * 4.0 - time);
float t = sin(uv.y * 36.0);
Add them to the color calculation: color *= d + s + t;
Play around with the values and introduce new effects!