User:Yiming/Proposal 2018/UserDocument/Modes/Snake

Edge Detection


LANPR applies Sobel edge detector on depth and normal pass to extract feature lines.

There are four values to adjust the effect of edge detection. By default, viewport will display edge detection result. Adjust different value, then when the extraction meet your desire, you can proceed to further post-processing steps.

Thinning
To trace feature pixels, edge detection result is processed with thinning algorithm, to ensure lines are in exact one pixel width. You can preview thinning result by selecting the display mode to Thinning.

note: It is recommended that you should adjust the values to achieve the effect that no large white regions are shown in viewport, this prevents messy vectorization result. Because different scene have different depth clipping planes, so the depth control values will have to be adjusted to meet this standard. In the future, automatic adaptation may be developed.

Vectorization


Image space edge detection and thinning results are sent to vectorization stage, if you enable Vectorization option. LANPR then trace the pixel features into a complete chain in CPU, and finally CPU send the result to GPU for rendering.

When vectorization is enabled, Line Styles can then be adjusted. Due to lack of edge type information, Snake mode can not adjust different line type individually. Line style can only be set uniformly.

Taper
Because the traced result is a long chain, Snake mode naturally have the ability to apply 1D styles on it. You can set taper strength and distance of influence. You can preview the effect realtime in the viewport.

note: Taper distance is not in absolute length currently. Different scene and camera configurations may give different result on this style.

Other Issues
As the other two modes have the advantage of speed and quality, Snake mode become less used in most of the conditions. The quality isn't the best but it is usable in nearly all scenes if properly adjusted. So Snake mode also has potential. Future development should also consider extending its feature.