Geometry snippets

Line equation from two points

To obtain a line equation of the form $Ax+By+C=0$ from two points $a$ and $b$, set:

${\begin{aligned}A&=a_{y}-b_{y}\\B&=b_{x}-a_{x}\\C&=a_{x}\cdot b_{y}-b_{x}\cdot a_{y}\end{aligned}}$

Source: https://bobobobo.wordpress.com/2008/01/07/solving-linear-equations-ax-by-c-0/

Distance from point to line segment

// https://www.iquilezles.org/www/articles/distfunctions2d/distfunctions2d.htm
static float sdLineSegment(glm::vec2 p, glm::vec2 a, glm::vec2 b)
{
    auto pa = p - a;
    auto ba = b - a;
    auto h = glm::clamp(glm::dot(pa, ba) / glm::dot(ba, ba), 0.f, 1.f);
    return glm::length(pa - ba * h);
}