CoronaLight - better representation of directionality

[romullus]

CoronaLight's directionality is not very intuitive to use as it is IMHO. I'd like to see its range expressed in degrees 0-90. Viewport representation also could be improved.

[Ondra]

we cannot do degrees, because there is no on/off angle we could show to user - it is rather a continuous drop in intensity with no associated angle to it

[romullus]

This is interesting. Would you care to explain a bit more how directionality works in Corona?

[Ondra]

Light directionality is basically a glossiness parameter of BRDF. You can even simulate CoronaLight with CoronaMtl:

Create a rectangle with CoronaMtl (your "light"), and create a 3ds Max spot light shining right onto the rectangle and on nothing else. The rectangle will reflect some of the light and illuminate other objects - so it is a "light". Now make the CoronaMtl assigned to the rectangle 100% reflective, IOR 999. Now by changing the glossiness parameter you will influence if the light will be scattered in only one direction, or in multiple directions. Congratulations - you now have fake CoronaLight with regular CoronaMtl! And: Reflection glossiness parameter == Light directionality parameter.

PS: if you want to try and render this,
a) make sure you have MSI=0
b) post results ;)

[FrostKiwi]

b) post results ;)

Tried out just for fun - Once I turn on reflectivity, the light is not being reflected anymore.
Also, apperently 999 IOR is broken? With 999 it still reflects the diffuse color of the 100% reflective sphere, just very slightly.
Only if I make sphere 100% black, then the image stays black, although I have 100 reflectivity.