{"id":2619,"date":"2018-07-21T19:21:46","date_gmt":"2018-07-21T19:21:46","guid":{"rendered":"http:\/\/julius-ihle.de\/?p=2619"},"modified":"2018-07-21T19:35:26","modified_gmt":"2018-07-21T19:35:26","slug":"lpe-quick-tip-1-light-path-splitting-for-transmission","status":"publish","type":"post","link":"https:\/\/julius-ihle.de\/?p=2619","title":{"rendered":"LPE Quick Tip #1: Light Path Splitting for Transmission"},"content":{"rendered":"

\"lpe01\"<\/a><\/p>\n

This will be a quick one.\u00a0Light Path Expressions offer a lot of flexibility over the AOV’s you would like to pass off to Compositing. Most modern path tracing render engines like Arnold, RenderMan, Blender’s Cycles, VRay, etc. have support for it by now. With LPE’s you can split pretty much any light path you desire, which brings me to\u00a0the solution to this first problem.<\/p>\n

<\/p>\n

Usually when you have a refractive object in your scene everything that is being refracted lands in 1 single AOV (usually called refraction, transmission, or something along those lines).
\nSo if I have a scene like this…<\/p>\n

\"01beauty0000\"<\/a><\/p>\n

 <\/p>\n

 <\/p>\n

My\u00a0transmission\u00a0AOV will usually look like this:
\n\"03refr0000\"<\/a><\/p>\n

 <\/p>\n

 <\/p>\n

…and my diffuse like this:<\/p>\n

\"02diff0000\"<\/a><\/p>\n

 <\/p>\n

 <\/p>\n

As you can imagine tweaking the diffuse in comp will be a bit of\u00a0a cumbersome task as the color of the teapot for example is in 2 different AOVs. Luckily what you can do is to modify the default LPE’s a bit to include\u00a0transmissive paths in other AOVs like diffuse, specular, subsurface scattering, etc.<\/p>\n

I won’t go into too much details of how it works. If you want a proper overview on LPE’s you can read up on them\u00a0HERE<\/a>.
\nThe default diffuse_direct looks like this usually:
\nC<RD>[<L.>O]
\nWhich simply means the lightpath Camera (C) -> Diffuse Reflection event (<RD>) -> Light Source \/ Emissive Object ([<L.>O])<\/p>\n

To make\u00a0all the light paths include refraction events as well you can\u00a0tell the light paths to look for zero or more\u00a0transmissive specular events before evaluating the rest of the light path.
\nSo if you modify the diffuse_direct like this:
\nC<TS>*<RD>[<L.>O]<\/p>\n

… then the diffuse will be a lot more useful for tweaking in Compositing:
\n\"04newdiff0000\"<\/a>
\n 
\n <\/p>\n

Likewise to make sure everything adds back together nicely you can modify the refraction pass to only include pure transmissive events:
\nC<TS>+[<L.>O]
\n\"05newrefr\"<\/a>
\n <\/p>\n

 <\/p>\n

As a TL;DR here is the stuff I personally like using:
\ndiffuse_direct: lpe:C<TS>*<RD>[<L.>O]
\ndiffuse_indirect: lpe:C<TS>*<RD>[DS]+[<L.>O]
\ndiffuse_albedo: lpe:C<TS>*<RD>A
\nspecular_direct: lpe:C<TS>*<RS>[<L.>O]
\nspecular_indirect: lpe:C<TS>*<RS>[DS]+[<L.>O]
\nrefraction: lpe:C<TS>+[<L.>O]
\nsss: lpe:C<TS>*<TD>[DS]*[<L.>O]
\n 
\n <\/p>\n

_________________________________________________<\/span>
\n If this post has helped you in any way you can express your gratefulness by using the Donate\u00a0<\/em>Button below to buy me a coffee! :)<\/span><\/span>
\n\"\"<\/a><\/p>\n

\n
3M5xNSV7g2NzVpHMqzYKhgoKJZ8CWa644m<\/span><\/span>
\n\"bc_ldgr_qrcode\"<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

This will be a quick one.\u00a0Light Path Expressions offer a lot of flexibility over the AOV’s you would like to pass off to Compositing. Most modern path tracing render engines like Arnold, RenderMan, Blender’s Cycles, VRay, etc. have support for it by now. With LPE’s you can split pretty much any light path you desire, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-2619","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p3MXK6-Gf","jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/julius-ihle.de\/index.php?rest_route=\/wp\/v2\/posts\/2619","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/julius-ihle.de\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/julius-ihle.de\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/julius-ihle.de\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/julius-ihle.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2619"}],"version-history":[{"count":11,"href":"https:\/\/julius-ihle.de\/index.php?rest_route=\/wp\/v2\/posts\/2619\/revisions"}],"predecessor-version":[{"id":2640,"href":"https:\/\/julius-ihle.de\/index.php?rest_route=\/wp\/v2\/posts\/2619\/revisions\/2640"}],"wp:attachment":[{"href":"https:\/\/julius-ihle.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2619"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/julius-ihle.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2619"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/julius-ihle.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2619"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}