A toon (or cel)
shader creates a cartoon-like image. A
common approach to toon shading is to limit the output colours to a set of
fixed intensity levels, implemented in a fragment shader.
Try writing your own toon shader to
output three different levels of red based on the light intensity (fIntensity)
at the fragment. For example,
the intensity is greater than 0.75, output pure bright red (r = 1).
if the intensity is greater than 0.5, output medium red (r = 0.6)
output dark red (r = 0.3)
Hint: Output colour (call it fragColour)
is a vec4 – the last component is 1.0, i.e., (R, G, B, 1)