TLinearGradient2D.h

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#pragma once
 
#include "Math/Function/TMathFunction2D.h"
#include "Math/TVector2.h"
 
#include <cmath>
#include <algorithm>
 
namespace ph::math
{
 
template<typename Value>
class TLinearGradient2D : public TMathFunction2D<Value>
{
public:
    static auto makeHorizontal(Value slope) -> TLinearGradient2D;
    static auto makeVertical(Value slope) -> TLinearGradient2D;
 
    TLinearGradient2D(TVector2<Value> direction, Value slope);
 
    Value evaluate(Value x, Value y) const override;
 
private:
    // Think in 3D, this is basically the direction of the ramp projected on the xy-plane
    TVector2<Value> m_unitDir;
    
    // Amount of value change in one unit amount of movement in the direction of `m_unitDir` 
    Value m_slope;
};
 
template<typename Value>
inline auto TLinearGradient2D<Value>::makeHorizontal(const Value slope)
-> TLinearGradient2D
{
    return TLinearGradient2D({1, 0}, slope);
}
 
template<typename Value>
inline auto TLinearGradient2D<Value>::makeVertical(const Value slope)
-> TLinearGradient2D
{
    return TLinearGradient2D({0, 1}, slope);
}
 
template<typename Value>
inline TLinearGradient2D<Value>::TLinearGradient2D(TVector2<Value> direction, Value slope)
    : m_unitDir(direction.normalize())
    , m_slope(slope)
{}
 
template<typename Value>
inline Value TLinearGradient2D<Value>::evaluate(const Value x, const Value y) const
{
    const Value projectedSignedLengthOnDir = m_unitDir.dot({x, y});
    return projectedSignedLengthOnDir * m_slope;
}
 
}// end namespace ph::math