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GSoC 2018: Bevel Modifier Improvements

Name

Rohan Rathi

Email / IRC

IRC

RohanRathi

Synopsis

The bevel modifier has a proposed list of changes and improvements planned. A non destructive alternative to the bevel tool, the modifier allows rounded corners for the geometry, and smooths out edges and corners. However the current modifier does not ensure correct normals and has various listed bugs which slows down artists workflow. Having written my own Weighted Normals modifier in last years Google Summer of Code. I am familiar with the modifier stack and its implementation and can work to provide good quality functionality on the modifier. I plan on adding critical discussed functionality that interact with the normals in the bevel modifier. I intend to keep the workflow as smooth and user friendly.

Benefits

The bevel modifier is widely used in modelling to chamfer edges and smoothen them out. Bevels are used to correct the shading of mesh, so as to make the edges blunt to give a solid and realistic look as opposed to non beveled objects.

I will work on adding a robust set of tools that will help improve the workflow of artists working with the bevel modifier so that many more artists will be able to utilise the modifier to complete their workflow. I plan on documenting the code related to my work on the modifier and work in close communication with the artists to best develop the set of functionality requested by them.

Project Details

Improve normal editing integration with Modifier

Proper support for custom normals is new found with work done last year. I propose to add much higher level support to the bevel modifier and modifiers in general. Given how much computation normals calculation requires it will be best to redefine structures and cache frequently used values to provide a base for any further edits and improvements to the bevel modifier. There are other requests for normals control in the modifier so I will work on adding them as well.

Harden Normals Option

Currently, after a bevel, the way vertex normals are calculated in Blender by default gives tilted vertex normals at the boundaries between the new polygons made along the beveled edges, and the original faces adjacent to those edges. By using smooth shading on the model, when hard body modeling, an artist would rather like that the original faces of something like a cube to be shaded flat after a bevel - the smooth shading would only affect the beveled edges and corners. However, currently we get shading artifacts due to the bent vertex normals and the way the faces are triangulated before shading.

With proper support for custom split normals it is now possible to adjust the vertex normals with specified algorithms. However this issue cannot be solved by the current weighted normals modifier, as with multi segment bevels the face area decreases requiring a different weighting mechanism to be used based on the segments of the bevel.

An advantage of normal support in bevel is to assign the newly created faces a face strength via the modifier itself. This would enable to keep the perfectly accurate normals which would otherwise be done through applying the modifier. This would also allow the bevels to be nondestructive so the sizes or the underlying geometry can be easily changed. Which would in turn improve the workflow and fasten asset creation.

Fix normal shading continuity

With specific meshes the shading continuity breaks giving non smooth shading. A possible solution us to have custom normal-editing option to bevel to fix up such continuity errors by changing the loop normals. This is a much requested feature for uniform shading in abstract models. However, the given fix would have to be fairly complex.

Project Schedule

I will use the community bonding period to discuss bugs and feature requests for the modifier in detail. I will then understand the codebase of the modifier to realise how I will rework it to support the changes requested. I will then devise a more comprehensive plan on how to provide a base for support of normals editing to bevel and plan to resolve the bugs listed. When coding begins, I will work to add the harden normals option to the modifier and implement various approaches discussed to figure out the best workflow and functionality. Before working on the options I will have to add structures to define how to support normal editing in the modifier with aim for future additions and better integration. After the bevel integration is finished I will prepare for first evaluation and revise and review the code. After evaluation I will finish with the functionality for hardened normals and discuss and review the changes to be incorporated to the work done so far. After this I will work on fixing the normal shading discontinuity with different meshes. I will finish the fix and polish the work I have done since then. I will also attempt to resolve the remaining bugs. I will then prepare for second evaluation. My college will start early August and I will wrap up most of the work by the last week of July. I will then spend the last few weeks to clean up and maintain the branch along with documenting the code.

Bio

I am a 20 years old student enrolled in Delhi Technological University studying Computer Science and Engineering, currently in my 3rd year of college. Having taken part in last years GSoC I have a good understanding of blenders codebase and the modifier workflow and implementation. I have been a regular contributor and have followed up on my work even after GSoC ended. I have been a blender user for several years, and plan on maintaining and revising the code for the bevel tool and my normal editing branch even after the program ends.