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This adds support for selective rendering of caustics in shadows of refractive objects. Example uses are rendering of underwater caustics and eye caustics. This is based on "Manifold Next Event Estimation", a method developed for production rendering. The idea is to selectively enable shadow caustics on a few objects in the scene where they have a big visual impact, without impacting render performance for the rest of the scene. The Shadow Caustic option must be manually enabled on light, caustic receiver and caster objects. For such light paths, the Filter Glossy option will be ignored and replaced by sharp caustics. Currently this method has a various limitations: * Only caustics in shadows of refractive objects work, which means no caustics from reflection or caustics that outside shadows. Only up to 4 refractive caustic bounces are supported. * Caustic caster objects should have smooth normals. * Not currently support for Metal GPU rendering. In the future this method may be extended for more general caustics. TECHNICAL DETAILS This code adds manifold next event estimation through refractive surface(s) as a new sampling technique for direct lighting, i.e. finding the point on the refractive surface(s) along the path to a light sample, which satisfies Fermat's principle for a given microfacet normal and the path's end points. This technique involves walking on the "specular manifold" using a pseudo newton solver. Such a manifold is defined by the specular constraint matrix from the manifold exploration framework [2]. For each refractive interface, this constraint is defined by enforcing that the generalized half-vector projection onto the interface local tangent plane is null. The newton solver guides the walk by linearizing the manifold locally before reprojecting the linear solution onto the refractive surface. See paper [1] for more details about the technique itself and [3] for the half-vector light transport formulation, from which it is derived. [1] Manifold Next Event Estimation Johannes Hanika, Marc Droske, and Luca Fascione. 2015. Comput. Graph. Forum 34, 4 (July 2015), 87–97. https://jo.dreggn.org/home/2015_mnee.pdf [2] Manifold exploration: a Markov Chain Monte Carlo technique for rendering scenes with difficult specular transport Wenzel Jakob and Steve Marschner. 2012. ACM Trans. Graph. 31, 4, Article 58 (July 2012), 13 pages. https://www.cs.cornell.edu/projects/manifolds-sg12/ [3] The Natural-Constraint Representation of the Path Space for Efficient Light Transport Simulation. Anton S. Kaplanyan, Johannes Hanika, and Carsten Dachsbacher. 2014. ACM Trans. Graph. 33, 4, Article 102 (July 2014), 13 pages. https://cg.ivd.kit.edu/english/HSLT.php The code for this samping technique was inserted at the light sampling stage (direct lighting). If the walk is successful, it turns off path regularization using a specialized flag in the path state (PATH_MNEE_SUCCESS). This flag tells the integrator not to blur the brdf roughness further down the path (in a child ray created from BSDF sampling). In addition, using a cascading mechanism of flag values, we cull connections to caustic lights for this and children rays, which should be resolved through MNEE. This mechanism also cancels the MIS bsdf counter part at the casutic receiver depth, in essence leaving MNEE as the only sampling technique from receivers through refractive casters to caustic lights. This choice might not be optimal when the light gets large wrt to the receiver, though this is usually not when you want to use MNEE. This connection culling strategy removes a fair amount of fireflies, at the cost of introducing a slight bias. Because of the selective nature of the culling mechanism, reflective caustics still benefit from the native path regularization, which further removes fireflies on other surfaces (bouncing light off casters). Differential Revision: https://developer.blender.org/D13533 |
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.. Keep this document short & concise, linking to external resources instead of including content in-line. See 'release/text/readme.html' for the end user read-me. Blender ======= Blender is the free and open source 3D creation suite. It supports the entirety of the 3D pipeline-modeling, rigging, animation, simulation, rendering, compositing, motion tracking and video editing. .. figure:: https://code.blender.org/wp-content/uploads/2018/12/springrg.jpg :scale: 50 % :align: center Project Pages ------------- - `Main Website <http://www.blender.org>`__ - `Reference Manual <https://docs.blender.org/manual/en/latest/index.html>`__ - `User Community <https://www.blender.org/community/>`__ Development ----------- - `Build Instructions <https://wiki.blender.org/wiki/Building_Blender>`__ - `Code Review & Bug Tracker <https://developer.blender.org>`__ - `Developer Forum <https://devtalk.blender.org>`__ - `Developer Documentation <https://wiki.blender.org>`__ License ------- Blender as a whole is licensed under the GNU General Public License, Version 3. Individual files may have a different, but compatible license. See `blender.org/about/license <https://www.blender.org/about/license>`__ for details.