piecewise_linear_interpolator.h

#pragma once
 
#include "interpolator.h"
 
namespace cgv {
namespace math {
 
template<typename T>
class piecewise_linear_interpolator : public interpolator<T> {
public:
    T interpolate(control_point_container<T> control_points, float t) const {
        size_t count = control_points.size();
 
        if(count == 0)
            return (T)0;
 
        if(count == 1)
            return control_points[0].second;
 
        t = cgv::math::clamp(t, control_points.min().first, control_points.max().first);
 
        if(t > control_points[0].first) {
            size_t idx = 0;
 
            for(size_t i = 1; i < count; ++i) {
                if(control_points[idx].first <= t && control_points[i].first > t)
                    break;
                idx = i;
            }
 
            if(idx < count - 1) {
                std::pair<float, T> n0 = control_points[idx];
                std::pair<float, T> n1 = control_points[idx + 1];
 
                float t0 = n0.first;
                float t1 = n1.first;
 
                float a = (t - t0) / (t1 - t0);
 
                return (T)((1.0f - a) * n0.second + a * n1.second);
            } else {
                return control_points[idx].second;
            }
        } else {
            return control_points[0].second;
        }
    }
 
    std::vector<T> interpolate(control_point_container<T> control_points, size_t n) const {
        size_t count = control_points.size();
 
        std::vector<T> data(n, (T)0);
 
        if(n == 0 || count == 0)
            return data;
 
        if(count == 1) {
            std::fill(data.begin(), data.end(), control_points[0].second);
            return data;
        }
 
        size_t l = 0;
        size_t r = 1;
 
        if(control_points.min().first > 0.0f)
            r = 0;
 
        float step = 1.0f / static_cast<float>(n - 1);
 
        for(size_t i = 0; i < n; ++i) {
            float t = static_cast<float>(i) * step;
 
            while(t > control_points[r].first && l < count - 1) {
                l = r;
                r = std::min(l + 1, count - 1);
            }
 
            if(l == r) {
                data[i] = (T)(control_points[r].second);
            } else {
                std::pair<float, T> n0 = control_points[l];
                std::pair<float, T> n1 = control_points[r];
 
                float t0 = n0.first;
                float t1 = n1.first;
 
                float a = (t - t0) / (t1 - t0);
 
                data[i] = (T)((1.0f - a) * n0.second + a * n1.second);
            }
        }
 
        return data;
    }
};
 
}
}