array_derivative2.h

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/*
**  array_derivative2.h
**
**  This is part of Shiokaze, a research-oriented fluid solver for computer graphics.
**  Created by Ryoichi Ando <rand@nii.ac.jp> on Feb 14, 2018.
**
**  Permission is hereby granted, free of charge, to any person obtaining a copy of
**  this software and associated documentation files (the "Software"), to deal in
**  the Software without restriction, including without limitation the rights to use,
**  copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
**  Software, and to permit persons to whom the Software is furnished to do so,
**  subject to the following conditions:
**
**  The above copyright notice and this permission notice shall be included in all copies
**  or substantial portions of the Software.
**
**  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
**  INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
**  PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
**  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
**  CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
**  OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
//
#ifndef SHKZ_ARRAY_DERIVATIVE2_H
#define SHKZ_ARRAY_DERIVATIVE2_H
//
#include "array2.h"
#include <cmath>
#include <cstdlib>
//
SHKZ_BEGIN_NAMESPACE
//
class array_derivative2 {
public:
    static void derivative_interpolate_coef( const shape2 &shape, const vec2d &p, vec2i indices[4], double coef[DIM2][4] ) {
        //
        double x = std::max(0.0,std::min(shape.w-1.,p[0]));
        double y = std::max(0.0,std::min(shape.h-1.,p[1]));
        int i = std::min(x,shape.w-2.);
        int j = std::min(y,shape.h-2.);
        //
        indices[0] = vec2i(i,j);
        indices[1] = vec2i(i+1,j);
        indices[2] = vec2i(i,j+1);
        indices[3] = vec2i(i+1,j+1);
        // x
        coef[0][0] = -(j+1-y);
        coef[0][1] = (j+1-y);
        coef[0][2] = -(y-j);
        coef[0][3] = (y-j);
        // y
        coef[1][0] = -(i+1-x);
        coef[1][1] = -(x-i);
        coef[1][2] = (i+1-x);
        coef[1][3] = (x-i);
    }
    template<class T>
    static void derivative( const array2<T> &array, const vec2d &p, T result[DIM2] ) {
        //
        T values[4]; vec2i indices[4]; double coef[DIM2][4];
        for( unsigned dim : DIMS2 ) result[dim] = T();
        derivative_interpolate_coef(array.shape(),p,indices,coef);
        for( unsigned dim : DIMS2 ) {
            for( unsigned n=0; n<4; ++n ) {
                result[dim] += coef[dim][n] * array(indices[n][0],indices[n][1]);
            }
        }
    }
    template<class T> static vec2<T> derivative( const array2<T> &array, const vec2d &origin, double dx, const vec2d &p ) {
        vec2<T> result;
        derivative<T>(array,(p-origin)/dx,result.v);
        return result/dx;
    }
};
//
SHKZ_END_NAMESPACE
//
#endif
//