jsmack
Karma lights now include ‘focus’ or directionality controls. Sample distribution is still naive AFAIK though, so you can't make a laser, or even remotely approach laser-focus.

YasinH

jsmack
Karma lights now include ‘focus’ or directionality controls. Sample distribution is still naive AFAIK though, so you can't make a laser, or even remotely approach laser-focus.

That's a bummer. Regardless of the noise issue, how would one implement its light material for Mantra?

jsmack

YasinH

jsmack
Karma lights now include ‘focus’ or directionality controls. Sample distribution is still naive AFAIK though, so you can't make a laser, or even remotely approach laser-focus.

That's a bummer. Regardless of the noise issue, how would one implement its light material for Mantra?

I don't know the math for the pdf of ‘directionality’ used by vray and the like, but the pdf for ggx is a nice gaussian distribution. And there's built in functions for getting the weight in a direction with a given focus exponent, as well as the integral over the pdf so you can normalize the power over the hemisphere. That's all I did when I added it lazily.

YasinH
The built-in function you are referring to is sample_hemisphereand create_pdf?

YasinH
Also, would you recommend using VEX code(similar to Asad light) or just VOP nodes for the light material?

jsmack

YasinH
The built-in function you are referring to is sample_hemisphereand create_pdf?

I think everything I needed was from the evalbsdf function. Sample functions are only needed for discreet samples (ray tracing). Since light shaders are continuous function, we only care about power scale in a given direction which is what the ‘eval’ argument of the evalbsdf function is. It may to be scaled by the pdf though, which is another argument of the same function.

YasinH
Also, would you recommend using VEX code(similar to Asad light) or just VOP nodes for the light material?

This is down to preference.

YasinH

jsmack

YasinH
The built-in function you are referring to is sample_hemisphereand create_pdf?

I think everything I needed was from the evalbsdf function. Sample functions are only needed for discreet samples (ray tracing). Since light shaders are continuous function, we only care about power scale in a given direction which is what the ‘eval’ argument of the evalbsdf function is. It may to be scaled by the pdf though, which is another argument of the same function.

YasinH
Also, would you recommend using VEX code(similar to Asad light) or just VOP nodes for the light material?

This is down to preference.

This is super helpful! Thank you. Something I'm trying to figure out eval_bsdf requires a bsdf as its first argument, while a light shader doesn't inherently have a bsdf, does it? Or should I build a custom bsdf in the light shader?

jsmack

YasinH

jsmack

YasinH
The built-in function you are referring to is sample_hemisphereand create_pdf?

I think everything I needed was from the evalbsdf function. Sample functions are only needed for discreet samples (ray tracing). Since light shaders are continuous function, we only care about power scale in a given direction which is what the ‘eval’ argument of the evalbsdf function is. It may to be scaled by the pdf though, which is another argument of the same function.

YasinH
Also, would you recommend using VEX code(similar to Asad light) or just VOP nodes for the light material?

This is down to preference.

This is super helpful! Thank you. Something I'm trying to figure out eval_bsdf requires a bsdf as its first argument, while a light shader doesn't inherently have a bsdf, does it? Or should I build a custom bsdf in the light shader?

Yeah, light shaders don't have their own bsdf normally. I'm abusing the ‘bsdf’ a generic function to get the mapping from angle to power. If you're using 18+ the ggx function can be used to create a ggx bsdf. Otherwise in pre-18 you'll have to use a cvex bsdf function.

vector b;
bsdf f = cvex_bsdf("diffuse_eval", "diffuse_sample", "label", "diffuse", "N", N);
b = eval_bsdf(f, -I, normalize(L), pow(cos(radians(90)), 3), bouncemask("all"));
L = normalize(b);

singhharry12
I think everything I needed was from the evalbsdf function. Sample functions are only needed for discreet samples (ray tracing). Since light shaders are continuous function, we only care about power scale in a given direction which is what the ‘eval’ argument of the evalbsdf function is. It may to be scaled by the pdf though, which is another argument of the same function.