UPBGE: Implement new Lamp Falloff

[lordloki]

• Inverse Square Cutoff for Lamps. Describes here:
  https://imdoingitwrong.wordpress.com/2011/01/31/light-attenuation/

Code by @DCubix

For feature request #728

[panzergame]

This patch seems coherent with the @adriansnetlis's report, even with the adding of a cutoff.

[panzergame]

cutoff is from 0 to 1 in the UI definition:

RNA_def_property_range(prop, 0.0f, 1.0f);

And here it could cause 0 division. You could limit it to 0.99.

[lordloki]

I just to check other shaders functions and the indeterminations are handle inside the shader instead of clamping the property range.

Perhaps we can optimize the lamp_falloff_invsquarecutoff function as follow:

void lamp_falloff_invsquarecutoff(float radius, float dist, float cutoff, out float visifac)  
{
	if (cutoff == 1.0 || radius == 0.0) {
		visifac = 0.0;
	}
	else {
		float d = max(dist - radius, 0.0);  
		if (d == 0.0) {
			visifac = 1.0;
		}
		else {
			float denom = d / radius + 1.0;  
			float att = 1.0 / (denom * denom);  
			att = (att - cutoff) / (1.0 - cutoff);  
			att = max(att, 0.0);  
			visifac = att;
		}
	}
}

What do you think?

[panzergame]

Is there's an interest for the user to set a cutoff to 1 or a zero radius ?

I agree for the second check level, you can even remove the max a check d <= 0.0.

Also about the UI, you can define a new RNA attribute named radius that is the same as distance attribute.

[lordloki]

Ok, changes done

[panzergame]

@adriansnetlis I invited you so that you could do a review on this patch if you please.

[adriansnetlis]

To me it looks like all has been implemented properly and the falloff is working.

When using Inverse Square Cutoff the Distance parameter in the user interface should say Radius instead for better clarification.

A comparsion between Cycles pathtrace and the falloff in game engine tells it's working well.
UPBGE:

Cycles:

[panzergame]

Generally I moved this compatibility part in versioning_upbge.c and add the same initialization in BKE lamp constructor (certainly BKE_lamp_new).

Also why are coeff_* changed ?

[lordloki]

Ok. Done.

I changed the coeff_* as they didn't have init values (setted to 0.0) but i will do in an independent commit.