path_fraction()

std::function< float(glm::vec2)> MayaFlux::Kinesis::path_fraction ( std::span< const glm::vec2 >  points )

inline

Normalized arc-length position of the closest point on a polyline.

Inverse to stroke_slider, which places the handle at a fraction of the path's total arc length. Finds the nearest point across all segments and returns its cumulative length divided by the total, so the handle follows the cursor along the path regardless of how far off the path it strays.

Cumulative lengths are computed once and captured; the returned callable allocates nothing per invocation.

Parameters

points

Ordered polyline vertices in NDC. Copied into the closure.

Returns

Callable producing a value in [0, 1]. Returns 0 for paths with fewer than two points or zero total length.

Definition at line 143 of file Projection.hpp.

{
    std::vector<glm::vec2> pts(points.begin(), points.end());
    std::vector<float> cumulative(pts.size(), 0.F);
 
    for (size_t i = 1; i < pts.size(); ++i)
        cumulative[i] = cumulative[i - 1] + glm::length(pts[i] - pts[i - 1]);
 
    const float total = pts.empty() ? 0.F : cumulative.back();
 
    return [pts = std::move(pts), cumulative = std::move(cumulative), total](
               glm::vec2 p) -> float {
        if (pts.size() < 2 || total <= 0.F)
            return 0.F;
 
        float best_d2 = std::numeric_limits<float>::max();
        float best_s = 0.F;
 
        for (size_t i = 0; i + 1 < pts.size(); ++i) {
            const glm::vec2 a = pts[i];
            const glm::vec2 ab = pts[i + 1] - a;
            const float len2 = glm::dot(ab, ab);
 
            const float t = len2 > 1e-12F
                ? glm::clamp(glm::dot(p - a, ab) / len2, 0.F, 1.F)
                : 0.F;
 
            const glm::vec2 diff = p - (a + t * ab);
            const float d2 = glm::dot(diff, diff);
 
            if (d2 < best_d2) {
                best_d2 = d2;
                best_s = cumulative[i] + t * std::sqrt(len2);
            }
        }
 
        return std::clamp(best_s / total, 0.F, 1.F);
    };
}

References a, and points.

Referenced by MayaFlux::Portal::Forma::Geometry::stroke_slider().

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