Assume the sensor is in the z plane and its width is arranged from -1 to 1 and
it's height is between -(ny/nx) to (ny/nx) (as in hw 3).
Emit photons uniformly from a sphere
with radius 0.1 and with center (0,0,3) and a uniform spectrum E(lambda) = constant.
Also have a diffuse sphere with the reflectance of the red square in the
macbeth color checker. Use center (1,0,3) and radius 0.5. If a photon
hits it, let it be reflected or absorbed probabilistically.
If it hits the light, absorb it.
Also add an infinite plane at z=1 with a "pinhole" of radius 0.05 at (0, 0, 1).
Only photons that pass through that hole are allowd to hit the sensor.
Finally, have the diffuse sphere move to (2,1,4) during the frame.
