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.
Tonal-art-map introduced in "Real-Time Hatching"
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.
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.
A Part of 2048x2048 Tonal-art-map ball pen texture
An unpatterned, uniform-intensity, and high-resolution tonal-art-map texture requires several hours for generation on 5GHz Intel i7 CPU + GTX2070 PC
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.
Tone Mapping Off
Tone Mapping On