Create 2D signed distance field (SDF) using points and polygons.
The accuracy is higher than that of 8ssedt method.
Inspired by Yuanming Hu's Taichi.
The MIT License (MIT)
Copyright (c) 2021, Jiang Ye
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When computing the gradient for a given point, I use Yuanming Hu's strategy because it performs more smoothly than mine.
The final gradient is grad = lerp(grad1, grad2, α) for x and y direction, respectively.
It means, if the point is close to the left (or bottom) border of the current cell, i.e. α -> 1,
we get more gradient of the current cell.
Otherwise, we get more gradient of the x + 1 (or y + 1) cell.
When deal with dynamic objects in a simulating program, recomputing SDF is necessary. In this project, I used an expensive one. But I have refined it in another project.