Jiffycrew Hatching (UE4) is an Unreal Engine 4 implementation of tonal-art-map-based hatching. The tonal-art-map-based hatching is a real-time rendering technique introduced in "Real-Time Hatching" SIGGRAPH paper (http://hhoppe.com/hatching.pdf), which uses a unique texture structure to draw a 3D scene using 2D strokes.
The key difference of this technique from stroke texture mapping is that it creates or removes strokes when depth changes while texture mapping scales the strokes textures. While the width of strokes changes if scaling occurs, this technique also preserves the stroke width and makes the scene rendering has a uniform stroke width. This property makes the whole scene rendering as if the strokes are drawn in the 2D screen space like in ordinary hand-drawing on papers, no matter where the camera is. So this is like magic: the strokes look like drawn on the screen but still are attached on objects and moves together.
The implementation of tonal-art-map-based hatching on UE4 is challenging because it requires multi-pass rendering which is not provided in UE4. We believe, because of this reason, that no UE4 implementation has been available since UE4 was launched, while we can find several Unity engine implementations.
To provide a unique and novel rendering style to UE4 game developers, Jiffycrew has researched possible solutions to overcome this limited condition for more than six months. We believe that we finally found a reasonable solution and now release this product in the Unreal Marketplace.
The Jiffycrew Hatching performs with deferred shading and gets UE4's physically-based rendering (PBR) pipeline result as input intensity. Honestly, if we gave up PBR, it would be so easy and straightforward to implement this product. This feature was the hardest part to provide, but we wanted to because we believe PBR is the reason why people are using UE4.
To enable tonal-art-map-based hatching, we also need to generate tonal-art-map stroke textures. Creating high-quality tonal art map stroke textures requires excellent hand drawing skills to make source strokes, deep understanding of tonal art map structure, and careful implementation of tonal-art-map building algorithm which is very briefly outlined in "Real-Time Hatching" paper. Although there are several implementations of hatching in Unity Asset Stores, the most implementation uses low-resolution tonal-art-map images copied from the paper. We could also find some tonal art map building program on the web, but those implementations were not entirely satisfactory to make high-quality results. In making this product, we carefully implemented the tonal art map building system and included three 2048x2048 tonal art maps for pencils, ball pens, and sign pens in the pack.
Jiffycrew Hatching also firstly introduce color hatching in the game industry. Although supporting color strokes is theoretically trivial, a real headache still exists in practice in handling colors between additive and subtractive color systems. See following revolutionary colorful hatching images that were realized after long headache.
As an artistic rendering, hatching should not be just a stroke mapping but should be considered as a reinterpretation of the scene. The artistic reinterpretation often requires exaggeration, emphasis, suppression, etc. of illumination. We included tone mapping of hatching in this product, and we believe this feature greatly helps such reinterpretation.