linear_gradient.hpp

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#ifndef NEFORCE_TUI_DOM_LINEAR_GRADIENT_HPP__
#define NEFORCE_TUI_DOM_LINEAR_GRADIENT_HPP__

 
#include "NeForce/core/container/vector.hpp"
#include "NeForce/core/utility/color.hpp"
#include "NeForce/core/utility/optional.hpp"
NEFORCE_BEGIN_NAMESPACE__
NEFORCE_BEGIN_TUI__


struct linear_gradient {
private:
    struct color_stop {
        _NEFORCE color color;     
        optional<float> position; 

        explicit color_stop(_NEFORCE color c, optional<float> pos = none) :
        color(move(c)),
        position(move(pos)) {}
    };
 
    float angle_ = 0.0F;       
    vector<color_stop> stops_; 
 
public:
    linear_gradient() {
        stops_.push_back(color_stop(_NEFORCE color::transparent(), 0.0F));
        stops_.push_back(color_stop(_NEFORCE color::black(), 1.0F));
    }

    linear_gradient(_NEFORCE color begin, struct color end) {
        stops_.push_back(color_stop(begin, 0.0F));
        stops_.push_back(color_stop(end, 1.0F));
    }

    linear_gradient& angle(const float a) {
        angle_ = a;
        return *this;
    }

    linear_gradient& add_stop(const struct color& c, optional<float> pos = none) {
        stops_.push_back(color_stop(c, pos));
        return *this;
    }

    NEFORCE_NODISCARD _NEFORCE color sample(float t) const {
        if (stops_.empty()) {
            return _NEFORCE color{};
        }
        if (stops_.size() == 1) {
            return stops_[0].color;
        }
 
        size_t idx = 0;
        for (size_t i = 0; i < stops_.size() - 1; ++i) {
            const float p1 = stops_[i].position.value_or(0.0F);
            const float p2 = stops_[i + 1].position.value_or(1.0F);
            if (t >= p1 && t <= p2) {
                idx = i;
                break;
            }
        }
 
        const color_stop& s1 = stops_[idx];
        const color_stop& s2 = stops_[idx + 1];
        const float p1 = s1.position.value_or(0.0F);
        const float p2 = s2.position.value_or(1.0F);
        const float range = p2 - p1;
        const float factor = (range > 0.0F) ? (t - p1) / range : 0.0F;
 
        return color::lerp(s1.color, s2.color, factor);
    }
};
 // TUI
 
NEFORCE_END_TUI__
NEFORCE_END_NAMESPACE__
#endif // NEFORCE_TUI_DOM_LINEAR_GRADIENT_HPP__