xbrz.cpp

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/*
   Copyright (C) 2014 - 2018 by Chris Beck <render787@gmail.com>
   Part of the Battle for Wesnoth Project https://www.wesnoth.org/
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY.
   See the COPYING file for more details.
 
   This is a derivative work of the xBRZ component of the HqMAME project
   by Zenju. The original Licensing statement follows, indented with //
   The primary changes are, syntactic to make it compile with C99+Boost,
   and to make it handle an alpha channel in the image in a manner proper
   for SDL.
 
   It is not possible to extend the MAME 'special exception' to all of
   the Battle for Wesnoth project, however, the special exception is
   granted for my derivative forms of this work.
*/
 
// ****************************************************************************
// * This file is part of the HqMAME project. It is distributed under         *
// * GNU General Public License: http://www.gnu.org/licenses/gpl.html         *
// * Copyright (C) Zenju (zenju AT gmx DOT de) - All Rights Reserved          *
// *                                                                          *
// * Additionally and as a special exception, the author gives permission     *
// * to link the code of this program with the MAME library (or with modified *
// * versions of MAME that use the same license as MAME), and distribute      *
// * linked combinations including the two. You must obey the GNU General     *
// * Public License in all respects for all of the code used other than MAME. *
// * If you modify this file, you may extend this exception to your version   *
// * of the file, but you are not obligated to do so. If you do not wish to   *
// * do so, delete this exception statement from your version.                *
// ****************************************************************************
 
#include "xBRZ/xbrz.hpp"
#include "config.hpp"
#include <cassert>
#include <cmath>
#include <algorithm>
 
#include <functional>
 
namespace
{
template <uint32_t N> inline
unsigned char getByte(uint32_t val) { return static_cast<unsigned char>((val >> (8 * N)) & 0xff); }
 
inline unsigned char getRed  (uint32_t val) { return getByte<2>(val); }
inline unsigned char getGreen(uint32_t val) { return getByte<1>(val); }
inline unsigned char getBlue (uint32_t val) { return getByte<0>(val); }
 
template <class T> inline
T abs(T value)
{
    //static_assert(std::is_signed<T>::value, "");
    return value < 0 ? -value : value;
}
 
const uint32_t redMask   = 0xff0000;
const uint32_t greenMask = 0x00ff00;
const uint32_t blueMask  = 0x0000ff;
const uint32_t alphaMask  = 0xff000000;
 
template <unsigned int N, unsigned int M> inline
void alphaBlend(uint32_t& dst, uint32_t col) //blend color over destination with opacity N / M
{
    //static_assert(N < 256, "possible overflow of (col & redMask) * N");
    //static_assert(M < 256, "possible overflow of (col & redMask  ) * N + (dst & redMask  ) * (M - N)");
    //static_assert(0 < N && N < M, "");
 
    //Note: I had to change this to perform alpha compositing -- xbrz assumes there is no alpha channel (and sets it to zero when it blends), our
    //sprites have alpha however.
    uint32_t col_alpha = col >> 24; // & with alphaMask is unnecessary
 
    if (!col_alpha) return;
 
    uint32_t dst_alpha = dst >> 24;
 
    if (!dst_alpha) {
        dst = col;
        return;
    }
 
    //uint32_t out_alpha = 0xffff - (((0xff - col_alpha)* (0xff - dst_alpha)) >> 8);
 
    //TODO: Figure out if there's some way to combine the multiplicative approached with the "averaged alpha", and to feedback the
    // alpha into the colors, without making it all very slow. Current approach looks okay, but I think shadows could be better,
    // also I think some units are getting 'black outlines' now because their black pixels with 0 alpha (background) are getting
    // averaged with their foreground.
 
    dst = (redMask   & ((col & redMask   ) * N + (dst & redMask   ) * (M - N)) / M) | //this works because 8 upper bits are free
          (greenMask & ((col & greenMask ) * N + (dst & greenMask ) * (M - N)) / M) |
          (blueMask  & ((col & blueMask  ) * N + (dst & blueMask  ) * (M - N)) / M) |
          (alphaMask & (((col_alpha       * N + dst_alpha * (M - N)) / M) << 24)); // need to downshift and upshift because of overflow
 
/*
    if (!(dst >> 24)) {
    dst = (col & (redMask | greenMask | blueMask)) |
              (((((col >> 24) * N) / M) << 24) & alphaMask);
    return;
    }
*/
/*
 
    double src_alpha = static_cast<double>(col >> 24) / 256; //xbrz basically assumes there is no alpha channel, our sprites have alpha however.
    double dst_alpha = static_cast<double>(dst >> 24) / 256;
 
    src_alpha = 1 - ((1 - src_alpha) * (1 - (N/M))); //apply blending arguments
 
    // For discussion of alpha compositing, see here: http://en.wikipedia.org/wiki/Alpha_compositing#Analytical_derivation_of_the_over_operator
    double out_alpha = 1 - ((1- src_alpha) * (1-dst_alpha));
 
    double src_coeff = src_alpha / out_alpha;
 
    double dst_coeff = dst_alpha / out_alpha;
 
 
 
    uint32_t red_val = (((col & redMask  ) >> 16) * src_coeff) + (((dst & redMask  ) >> 16) * dst_coeff);
 
    uint32_t grn_val = (((col & greenMask) >> 8 ) * src_coeff) + (((dst & greenMask) >> 8 ) * dst_coeff);
 
    uint32_t blu_val = (((col & blueMask ) >> 0 ) * src_coeff) + (((dst & blueMask ) >> 0 ) * dst_coeff);
 
 
 
    dst = (red_val << 16) |
          (grn_val << 8 ) |
          (blu_val << 0) |
          (alphaMask & (static_cast<uint32_t>(256 * out_alpha) << 24));
//    0xff000000; //adding this to try to get rid of black outlines, there are code comments that say 0 is transparent for SDL, not 255 -- iceiceice
*/
}
 
 
//inline
//double fastSqrt(double n)
//{
//    __asm //speeds up xBRZ by about 9% compared to std::sqrt
//    {
//        fld n
//        fsqrt
//    }
//}
//
 
#if 0
inline
uint32_t alphaBlend2(uint32_t pix1, uint32_t pix2, double alpha)
{
    return (redMask   & static_cast<uint32_t>((pix1 & redMask  ) * alpha + (pix2 & redMask  ) * (1 - alpha))) |
           (greenMask & static_cast<uint32_t>((pix1 & greenMask) * alpha + (pix2 & greenMask) * (1 - alpha))) |
           (blueMask  & static_cast<uint32_t>((pix1 & blueMask ) * alpha + (pix2 & blueMask ) * (1 - alpha)));
}
#endif
 
uint32_t*       byteAdvance(      uint32_t* ptr, int bytes) {  return reinterpret_cast<      uint32_t*>(reinterpret_cast<      char*>(ptr) + bytes); }
const uint32_t* byteAdvance(const uint32_t* ptr, int bytes) {  return reinterpret_cast<const uint32_t*>(reinterpret_cast<const char*>(ptr) + bytes); }
 
 
//fill block  with the given color
inline
void fillBlock(uint32_t* trg, int pitch, uint32_t col, int blockWidth, int blockHeight)
{
    //for (int y = 0; y < blockHeight; ++y, trg = byteAdvance(trg, pitch))
    //    std::fill(trg, trg + blockWidth, col);
 
    for (int y = 0; y < blockHeight; ++y, trg = byteAdvance(trg, pitch))
        for (int x = 0; x < blockWidth; ++x)
            trg[x] = col;
}
 
inline
void fillBlock(uint32_t* trg, int pitch, uint32_t col, int n) { fillBlock(trg, pitch, col, n, n); }
 
 
#ifdef _MSC_VER
#define FORCE_INLINE __forceinline
#elif defined __GNUC__
#define FORCE_INLINE __attribute__((always_inline)) inline
#else
#define FORCE_INLINE inline
#endif
 
 
enum RotationDegree //clock-wise
{
    ROT_0,
    ROT_90,
    ROT_180,
    ROT_270
};
 
//calculate input matrix coordinates after rotation at compile time
template <RotationDegree rotDeg, size_t I, size_t J, size_t N>
struct MatrixRotation;
 
template <size_t I, size_t J, size_t N>
struct MatrixRotation<ROT_0, I, J, N>
{
    static const size_t I_old = I;
    static const size_t J_old = J;
};
 
template <RotationDegree rotDeg, size_t I, size_t J, size_t N> //(i, j) = (row, col) indices, N = size of (square) matrix
struct MatrixRotation
{
    static const size_t I_old = N - 1 - MatrixRotation<static_cast<RotationDegree>(rotDeg - 1), I, J, N>::J_old; //old coordinates before rotation!
    static const size_t J_old =         MatrixRotation<static_cast<RotationDegree>(rotDeg - 1), I, J, N>::I_old; //
};
 
 
template <size_t N, RotationDegree rotDeg>
class OutputMatrix
{
public:
    OutputMatrix(uint32_t* out, int outWidth) : //access matrix area, top-left at position "out" for image with given width
        out_(out),
        outWidth_(outWidth) {}
 
    template <size_t I, size_t J>
    uint32_t& ref() const
    {
        static const size_t I_old = MatrixRotation<rotDeg, I, J, N>::I_old;
        static const size_t J_old = MatrixRotation<rotDeg, I, J, N>::J_old;
        return *(out_ + J_old + I_old * outWidth_);
    }
 
private:
    uint32_t* out_;
    const int outWidth_;
};
 
 
template <class T> inline
T square(T value) { return value * value; }
 
 
/*
inline
void rgbtoLuv(uint32_t c, double& L, double& u, double& v)
{
    //http://www.easyrgb.com/index.php?X=MATH&H=02#text2
    double r = getRed  (c) / 255.0;
    double g = getGreen(c) / 255.0;
    double b = getBlue (c) / 255.0;
 
    if ( r > 0.04045 )
        r = std::pow(( ( r + 0.055 ) / 1.055 ) , 2.4);
    else
        r /= 12.92;
    if ( g > 0.04045 )
        g = std::pow(( ( g + 0.055 ) / 1.055 ) , 2.4);
    else
        g /=  12.92;
    if ( b > 0.04045 )
        b  = std::pow(( ( b + 0.055 ) / 1.055 ) , 2.4);
    else
        b /=  12.92;
 
    r *= 100;
    g *= 100;
    b *= 100;
 
    double x = 0.4124564 * r + 0.3575761 * g + 0.1804375 * b;
    double y = 0.2126729 * r + 0.7151522 * g + 0.0721750 * b;
    double z = 0.0193339 * r + 0.1191920 * g + 0.9503041 * b;
    //---------------------
    double var_U =  4 * x  / ( x +  15 * y  +  3 * z  );
    double var_V =  9 * y  / ( x +  15 * y  +  3 * z  );
    double var_Y = y / 100;
 
    if ( var_Y > 0.008856 ) var_Y = std::pow(var_Y , 1.0/3 );
    else                    var_Y =  7.787 * var_Y  +  16.0 / 116;
 
    const double ref_X =  95.047;        //Observer= 2 (degrees), Illuminant= D65
    const double ref_Y = 100.000;
    const double ref_Z = 108.883;
 
    const double ref_U = ( 4 * ref_X ) / ( ref_X + ( 15 * ref_Y ) + ( 3 * ref_Z ) );
    const double ref_V = ( 9 * ref_Y ) / ( ref_X + ( 15 * ref_Y ) + ( 3 * ref_Z ) );
 
    L = ( 116 * var_Y ) - 16;
    u = 13 * L * ( var_U - ref_U );
    v = 13 * L * ( var_V - ref_V );
}
*/
 
#if 0
inline
void rgbtoLab(uint32_t c, unsigned char& L, signed char& A, signed char& B)
{
    //code: http://www.easyrgb.com/index.php?X=MATH
    //test: http://www.workwithcolor.com/color-converter-01.htm
    //------RGB to XYZ------
    double r = getRed  (c) / 255.0;
    double g = getGreen(c) / 255.0;
    double b = getBlue (c) / 255.0;
 
    r = r > 0.04045 ? std::pow(( r + 0.055 ) / 1.055, 2.4) : r / 12.92;
    r = g > 0.04045 ? std::pow(( g + 0.055 ) / 1.055, 2.4) : g / 12.92;
    r = b > 0.04045 ? std::pow(( b + 0.055 ) / 1.055, 2.4) : b / 12.92;
 
    r *= 100;
    g *= 100;
    b *= 100;
 
    double x = 0.4124564 * r + 0.3575761 * g + 0.1804375 * b;
    double y = 0.2126729 * r + 0.7151522 * g + 0.0721750 * b;
    double z = 0.0193339 * r + 0.1191920 * g + 0.9503041 * b;
    //------XYZ to Lab------
    const double refX = 95.047;  //
    const double refY = 100.000; //Observer= 2 (degrees), Illuminant= D65
    const double refZ = 108.883; //
    double var_X = x / refX;
    double var_Y = y / refY;
    double var_Z = z / refZ;
 
    var_X = var_X > 0.008856 ? std::pow(var_X, 1.0 / 3) : 7.787 * var_X + 4.0 / 29;
    var_Y = var_Y > 0.008856 ? std::pow(var_Y, 1.0 / 3) : 7.787 * var_Y + 4.0 / 29;
    var_Z = var_Z > 0.008856 ? std::pow(var_Z, 1.0 / 3) : 7.787 * var_Z + 4.0 / 29;
 
    L = static_cast<unsigned char>(116 * var_Y  - 16);
    A = static_cast<  signed char>(500 * (var_X - var_Y));
    B = static_cast<  signed char>(200 * (var_Y - var_Z));
};
#endif
 
#if 0
inline
double distLAB(uint32_t pix1, uint32_t pix2)
{
    unsigned char L1 = 0; //[0, 100]
    signed   char a1 = 0; //[-128, 127]
    signed   char b1 = 0; //[-128, 127]
    rgbtoLab(pix1, L1, a1, b1);
 
    unsigned char L2 = 0;
    signed   char a2 = 0;
    signed   char b2 = 0;
    rgbtoLab(pix2, L2, a2, b2);
 
    //-----------------------------
    //http://www.easyrgb.com/index.php?X=DELT
 
    //Delta E/CIE76
    return std::sqrt(square(1.0 * L1 - L2) +
                     square(1.0 * a1 - a2) +
                     square(1.0 * b1 - b2));
}
#endif
 
/*
inline
void rgbtoHsl(uint32_t c, double& h, double& s, double& l)
{
    //http://www.easyrgb.com/index.php?X=MATH&H=18#text18
    const int r = getRed  (c);
    const int g = getGreen(c);
    const int b = getBlue (c);
 
    const int varMin = numeric::min(r, g, b);
    const int varMax = numeric::max(r, g, b);
    const int delMax = varMax - varMin;
 
    l = (varMax + varMin) / 2.0 / 255.0;
 
    if (delMax == 0) //gray, no chroma...
    {
        h = 0;
        s = 0;
    }
    else
    {
        s = l < 0.5 ?
            delMax / (1.0 * varMax + varMin) :
            delMax / (2.0 * 255 - varMax - varMin);
 
        double delR = ((varMax - r) / 6.0 + delMax / 2.0) / delMax;
        double delG = ((varMax - g) / 6.0 + delMax / 2.0) / delMax;
        double delB = ((varMax - b) / 6.0 + delMax / 2.0) / delMax;
 
        if (r == varMax)
            h = delB - delG;
        else if (g == varMax)
            h = 1 / 3.0 + delR - delB;
        else if (b == varMax)
            h = 2 / 3.0 + delG - delR;
 
        if (h < 0)
            h += 1;
        if (h > 1)
            h -= 1;
    }
}
 
inline
double distHSL(uint32_t pix1, uint32_t pix2, double lightningWeight)
{
    double h1 = 0;
    double s1 = 0;
    double l1 = 0;
    rgbtoHsl(pix1, h1, s1, l1);
    double h2 = 0;
    double s2 = 0;
    double l2 = 0;
    rgbtoHsl(pix2, h2, s2, l2);
 
    //HSL is in cylindric coordinatates where L represents height, S radius, H angle,
    //however we interpret the cylinder as a bi-conic solid with top/bottom radius 0, middle radius 1
    assert(0 <= h1 && h1 <= 1);
    assert(0 <= h2 && h2 <= 1);
 
    double r1 = l1 < 0.5 ?
                l1 * 2 :
                2 - l1 * 2;
 
    double x1 = r1 * s1 * std::cos(h1 * 2 * numeric::pi);
    double y1 = r1 * s1 * std::sin(h1 * 2 * numeric::pi);
    double z1 = l1;
 
    double r2 = l2 < 0.5 ?
                l2 * 2 :
                2 - l2 * 2;
 
    double x2 = r2 * s2 * std::cos(h2 * 2 * numeric::pi);
    double y2 = r2 * s2 * std::sin(h2 * 2 * numeric::pi);
    double z2 = l2;
 
    return 255 * std::sqrt(square(x1 - x2) + square(y1 - y2) +  square(lightningWeight * (z1 - z2)));
}
*/
 
#if 0
inline
double distRGB(uint32_t pix1, uint32_t pix2)
{
    const double r_diff = static_cast<int>(getRed  (pix1)) - getRed  (pix2);
    const double g_diff = static_cast<int>(getGreen(pix1)) - getGreen(pix2);
    const double b_diff = static_cast<int>(getBlue (pix1)) - getBlue (pix2);
 
    //euklidean RGB distance
    return std::sqrt(square(r_diff) + square(g_diff) + square(b_diff));
}
#endif
 
#if 0
inline
double distNonLinearRGB(uint32_t pix1, uint32_t pix2)
{
    //non-linear rgb: http://www.compuphase.com/cmetric.htm
    const double r_diff = static_cast<int>(getRed  (pix1)) - getRed  (pix2);
    const double g_diff = static_cast<int>(getGreen(pix1)) - getGreen(pix2);
    const double b_diff = static_cast<int>(getBlue (pix1)) - getBlue (pix2);
 
    const double r_avg = (static_cast<double>(getRed(pix1)) + getRed(pix2)) / 2;
    return std::sqrt((2 + r_avg / 255) * square(r_diff) + 4 * square(g_diff) + (2 + (255 - r_avg) / 255) * square(b_diff));
}
#endif
 
inline
double distYCbCr(uint32_t pix1, uint32_t pix2, double lumaWeight)
{
    //http://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion
    //YCbCr conversion is a matrix multiplication => take advantage of linearity by subtracting first!
    const int r_diff = static_cast<int>(getRed  (pix1)) - getRed  (pix2); //we may delay division by 255 to after matrix multiplication
    const int g_diff = static_cast<int>(getGreen(pix1)) - getGreen(pix2); //
    const int b_diff = static_cast<int>(getBlue (pix1)) - getBlue (pix2); //subtraction for int is noticeable faster than for double!
 
    const double k_b = 0.0722; //ITU-R BT.709 conversion
    const double k_r = 0.2126; //
    const double k_g = 1 - k_b - k_r;
 
    const double scale_b = 0.5 / (1 - k_b);
    const double scale_r = 0.5 / (1 - k_r);
 
    const double y   = k_r * r_diff + k_g * g_diff + k_b * b_diff; //[!], analog YCbCr!
    const double c_b = scale_b * (b_diff - y);
    const double c_r = scale_r * (r_diff - y);
 
    //we skip division by 255 to have similar range like other distance functions
    return std::sqrt(square(lumaWeight * y) + square(c_b) +  square(c_r));
}
 
#if 0
inline
double distYUV(uint32_t pix1, uint32_t pix2, double luminanceWeight)
{
    //perf: it's not worthwhile to buffer the YUV-conversion, the direct code is faster by ~ 6%
    //since RGB -> YUV conversion is essentially a matrix multiplication, we can calculate the RGB diff before the conversion (distributive property)
    const double r_diff = static_cast<int>(getRed  (pix1)) - getRed  (pix2);
    const double g_diff = static_cast<int>(getGreen(pix1)) - getGreen(pix2);
    const double b_diff = static_cast<int>(getBlue (pix1)) - getBlue (pix2);
 
    //http://en.wikipedia.org/wiki/YUV#Conversion_to.2Ffrom_RGB
    const double w_b = 0.114;
    const double w_r = 0.299;
    const double w_g = 1 - w_r - w_b;
 
    const double u_max = 0.436;
    const double v_max = 0.615;
 
    const double scale_u = u_max / (1 - w_b);
    const double scale_v = v_max / (1 - w_r);
 
    double y = w_r * r_diff + w_g * g_diff + w_b * b_diff;//value range: 255 * [-1, 1]
    double u = scale_u * (b_diff - y);                    //value range: 255 * 2 * u_max * [-1, 1]
    double v = scale_v * (r_diff - y);                    //value range: 255 * 2 * v_max * [-1, 1]
 
#ifndef NDEBUG
    const double eps = 0.5;
#endif
    assert(std::abs(y) <= 255 + eps);
    assert(std::abs(u) <= 255 * 2 * u_max + eps);
    assert(std::abs(v) <= 255 * 2 * v_max + eps);
 
    return std::sqrt(square(luminanceWeight * y) + square(u) +  square(v));
}
#endif
 
inline
double colorDist(uint32_t pix1, uint32_t pix2, double luminanceWeight)
{
    if (pix1 == pix2) //about 8% perf boost
        return 0;
 
    //return distHSL(pix1, pix2, luminanceWeight);
    //return distRGB(pix1, pix2);
    //return distLAB(pix1, pix2);
    //return distNonLinearRGB(pix1, pix2);
    //return distYUV(pix1, pix2, luminanceWeight);
 
    return distYCbCr(pix1, pix2, luminanceWeight);
}
 
 
enum BlendType
{
    BLEND_NONE = 0,
    BLEND_NORMAL,   //a normal indication to blend
    BLEND_DOMINANT, //a strong indication to blend
    //attention: BlendType must fit into the value range of 2 bit!!!
};
 
struct BlendResult
{
    BlendType
    /**/blend_f, blend_g,
    /**/blend_j, blend_k;
 
    BlendResult() : blend_f(), blend_g(), blend_j(), blend_k() {}
};
 
 
struct Kernel_4x4 //kernel for preprocessing step
{
    uint32_t
    /**/a=0, b=0, c=0, d=0,
    /**/e=0, f=0, g=0, h=0,
    /**/i=0, j=0, k=0, l=0,
    /**/m=0, n=0, o=0, p=0;
 
    Kernel_4x4() {}
};
 
/*
input kernel area naming convention:
-----------------
| A | B | C | D |
----|---|---|---|
| E | F | G | H |   //evaluate the four corners between F, G, J, K
----|---|---|---|   //input pixel is at position F
| I | J | K | L |
----|---|---|---|
| M | N | O | P |
-----------------
*/
FORCE_INLINE //detect blend direction
BlendResult preProcessCorners(const Kernel_4x4& ker, const xbrz::ScalerCfg& cfg) //result: F, G, J, K corners of "GradientType"
{
    BlendResult result;
 
    if ((ker.f == ker.g &&
         ker.j == ker.k) ||
        (ker.f == ker.j &&
         ker.g == ker.k))
        return result;
 
    auto dist = [&cfg](uint32_t col1, uint32_t col2) { return colorDist(col1, col2, cfg.luminanceWeight_); };
 
    const int weight = 4;
    double jg = dist(ker.i, ker.f) + dist(ker.f, ker.c) + dist(ker.n, ker.k) + dist(ker.k, ker.h) + weight * dist(ker.j, ker.g);
    double fk = dist(ker.e, ker.j) + dist(ker.j, ker.o) + dist(ker.b, ker.g) + dist(ker.g, ker.l) + weight * dist(ker.f, ker.k);
 
    if (jg < fk) //test sample: 70% of values max(jg, fk) / min(jg, fk) are between 1.1 and 3.7 with median being 1.8
    {
        const bool dominantGradient = cfg.dominantDirectionThreshold * jg < fk;
        if (ker.f != ker.g && ker.f != ker.j)
            result.blend_f = dominantGradient ? BLEND_DOMINANT : BLEND_NORMAL;
 
        if (ker.k != ker.j && ker.k != ker.g)
            result.blend_k = dominantGradient ? BLEND_DOMINANT : BLEND_NORMAL;
    }
    else if (fk < jg)
    {
        const bool dominantGradient = cfg.dominantDirectionThreshold * fk < jg;
        if (ker.j != ker.f && ker.j != ker.k)
            result.blend_j = dominantGradient ? BLEND_DOMINANT : BLEND_NORMAL;
 
        if (ker.g != ker.f && ker.g != ker.k)
            result.blend_g = dominantGradient ? BLEND_DOMINANT : BLEND_NORMAL;
    }
    return result;
}
 
struct Kernel_3x3
{
    uint32_t
    /**/a=0,  b=0,  c=0,
    /**/d=0,  e=0,  f=0,
    /**/g=0,  h=0,  i=0;
 
    Kernel_3x3() {}
};
 
#define DEF_GETTER(x) template <RotationDegree rotDeg> uint32_t inline get_##x(const Kernel_3x3& ker) { return ker.x; }
//we cannot and NEED NOT write "ker.##x" since ## concatenates preprocessor tokens but "." is not a token
DEF_GETTER(a) DEF_GETTER(b) DEF_GETTER(c)
DEF_GETTER(d) DEF_GETTER(e) DEF_GETTER(f)
DEF_GETTER(g) DEF_GETTER(h) DEF_GETTER(i)
#undef DEF_GETTER
 
#define DEF_GETTER(x, y) template <> inline uint32_t get_##x<ROT_90>(const Kernel_3x3& ker) { return ker.y; }
/*DEF_GETTER(a, g)*/ DEF_GETTER(b, d) DEF_GETTER(c, a)
DEF_GETTER(d, h) DEF_GETTER(e, e) DEF_GETTER(f, b)
DEF_GETTER(g, i) DEF_GETTER(h, f) DEF_GETTER(i, c)
#undef DEF_GETTER
 
#define DEF_GETTER(x, y) template <> inline uint32_t get_##x<ROT_180>(const Kernel_3x3& ker) { return ker.y; }
/*DEF_GETTER(a, i)*/ DEF_GETTER(b, h) DEF_GETTER(c, g)
DEF_GETTER(d, f) DEF_GETTER(e, e) DEF_GETTER(f, d)
DEF_GETTER(g, c) DEF_GETTER(h, b) DEF_GETTER(i, a)
#undef DEF_GETTER
 
#define DEF_GETTER(x, y) template <> inline uint32_t get_##x<ROT_270>(const Kernel_3x3& ker) { return ker.y; }
/*DEF_GETTER(a, c)*/ DEF_GETTER(b, f) DEF_GETTER(c, i)
DEF_GETTER(d, b) DEF_GETTER(e, e) DEF_GETTER(f, h)
DEF_GETTER(g, a) DEF_GETTER(h, d) DEF_GETTER(i, g)
#undef DEF_GETTER
 
//compress four blend types into a single byte
//inline BlendType getTopL   (unsigned char b) { return static_cast<BlendType>(0x3 & b); }
inline BlendType getTopR   (unsigned char b) { return static_cast<BlendType>(0x3 & (b >> 2)); }
inline BlendType getBottomR(unsigned char b) { return static_cast<BlendType>(0x3 & (b >> 4)); }
inline BlendType getBottomL(unsigned char b) { return static_cast<BlendType>(0x3 & (b >> 6)); }
 
inline void setTopL   (unsigned char& b, BlendType bt) { b |= bt; } //buffer is assumed to be initialized before preprocessing!
inline void setTopR   (unsigned char& b, BlendType bt) { b |= (bt << 2); }
inline void setBottomR(unsigned char& b, BlendType bt) { b |= (bt << 4); }
inline void setBottomL(unsigned char& b, BlendType bt) { b |= (bt << 6); }
 
inline bool blendingNeeded(unsigned char b) { return b != 0; }
 
template <RotationDegree rotDeg> inline
unsigned char rotateBlendInfo(unsigned char b) { return b; }
template <> inline unsigned char rotateBlendInfo<ROT_90 >(unsigned char b) { return ((b << 2) | (b >> 6)) & 0xff; }
template <> inline unsigned char rotateBlendInfo<ROT_180>(unsigned char b) { return ((b << 4) | (b >> 4)) & 0xff; }
template <> inline unsigned char rotateBlendInfo<ROT_270>(unsigned char b) { return ((b << 6) | (b >> 2)) & 0xff; }
 
 
#ifndef NDEBUG
int debugPixelX = -1;
int debugPixelY = 84;
bool breakIntoDebugger = false;
#endif
 
/*
input kernel area naming convention:
-------------
| A | B | C |
----|---|---|
| D | E | F | //input pixel is at position E
----|---|---|
| G | H | I |
-------------
*/
template <class Scaler, RotationDegree rotDeg>
FORCE_INLINE //perf: quite worth it!
void scalePixel(const Kernel_3x3& ker,
                uint32_t* target, int trgWidth,
                unsigned char blendInfo, //result of preprocessing all four corners of pixel "e"
                const xbrz::ScalerCfg& cfg)
{
#define a get_a<rotDeg>(ker)
#define b get_b<rotDeg>(ker)
#define c get_c<rotDeg>(ker)
#define d get_d<rotDeg>(ker)
#define e get_e<rotDeg>(ker)
#define f get_f<rotDeg>(ker)
#define g get_g<rotDeg>(ker)
#define h get_h<rotDeg>(ker)
#define i get_i<rotDeg>(ker)
 
#ifndef NDEBUG
    (void) breakIntoDebugger;
    //if (breakIntoDebugger)
    //    __debugbreak(); //__asm int 3;
#endif
 
    const unsigned char blend = rotateBlendInfo<rotDeg>(blendInfo);
 
    if (getBottomR(blend) >= BLEND_NORMAL)
    {
        auto eq   = [&cfg](uint32_t col1, uint32_t col2) { return colorDist(col1, col2, cfg.luminanceWeight_) < cfg.equalColorTolerance_; };
 
        auto dist = [&cfg](uint32_t col1, uint32_t col2) { return colorDist(col1, col2, cfg.luminanceWeight_); };
 
        const uint32_t px = dist(e, f) <= dist(e, h) ? f : h; //choose most similar color
 
        OutputMatrix<Scaler::scale, rotDeg> out(target, trgWidth);
 
        bool doLineBlend = true;
        {
            if (getBottomR(blend) >= BLEND_DOMINANT)
                doLineBlend = true;
 
            //make sure there is no second blending in an adjacent rotation for this pixel: handles insular pixels, mario eyes
            else if (getTopR(blend) != BLEND_NONE && !eq(e, g)) //but support double-blending for 90 (degrees) corners
                doLineBlend = false;
            else if (getBottomL(blend) != BLEND_NONE && !eq(e, c))
                doLineBlend = false;
 
            //no full blending for L-shapes; blend corner only (handles "mario mushroom eyes")
            else if (eq(g, h) &&  eq(h , i) && eq(i, f) && eq(f, c) && !eq(e, i))
                doLineBlend = false;
 
            else doLineBlend = true;
        }
 
        if (doLineBlend)
        {
            const double fg = dist(f, g); //test sample: 70% of values max(fg, hc) / min(fg, hc) are between 1.1 and 3.7 with median being 1.9
            const double hc = dist(h, c); //
 
            const bool haveShallowLine = cfg.steepDirectionThreshold * fg <= hc && e != g && d != g;
            const bool haveSteepLine   = cfg.steepDirectionThreshold * hc <= fg && e != c && b != c;
 
            if (haveShallowLine)
            {
                if (haveSteepLine)
                    Scaler::blendLineSteepAndShallow(px, out);
                else
                    Scaler::blendLineShallow(px, out);
            }
            else
            {
                if (haveSteepLine)
                    Scaler::blendLineSteep(px, out);
                else
                    Scaler::blendLineDiagonal(px,out);
            }
        }
        else
            Scaler::blendCorner(px, out);
    }
 
#undef a
#undef b
#undef c
#undef d
#undef e
#undef f
#undef g
#undef h
#undef i
}
 
 
template <class Scaler> //scaler policy: see "Scaler2x" reference implementation
void scaleImage(const uint32_t* src, uint32_t* trg, int srcWidth, int srcHeight, const xbrz::ScalerCfg& cfg, int yFirst, int yLast)
{
    yFirst = std::max(yFirst, 0);
    yLast  = std::min(yLast, srcHeight);
    if (yFirst >= yLast || srcWidth <= 0)
        return;
 
    const int trgWidth = srcWidth * Scaler::scale;
 
    //"use" space at the end of the image as temporary buffer for "on the fly preprocessing": we even could use larger area of
    //"sizeof(uint32_t) * srcWidth * (yLast - yFirst)" bytes without risk of accidental overwriting before accessing
    const int bufferSize = srcWidth;
    unsigned char* preProcBuffer = reinterpret_cast<unsigned char*>(trg + yLast * Scaler::scale * trgWidth) - bufferSize;
    std::fill(preProcBuffer, preProcBuffer + bufferSize, static_cast<unsigned char>(0));
    //static_assert(BLEND_NONE == 0, "");
 
    //initialize preprocessing buffer for first row: detect upper left and right corner blending
    //this cannot be optimized for adjacent processing stripes; we must not allow for a memory race condition!
    if (yFirst > 0)
    {
        const int y = yFirst - 1;
 
        const uint32_t* s_m1 = src + srcWidth * std::max(y - 1, 0);
        const uint32_t* s_0  = src + srcWidth * y; //center line
        const uint32_t* s_p1 = src + srcWidth * std::min(y + 1, srcHeight - 1);
        const uint32_t* s_p2 = src + srcWidth * std::min(y + 2, srcHeight - 1);
 
        for (int x = 0; x < srcWidth; ++x)
        {
            const int x_m1 = std::max(x - 1, 0);
            const int x_p1 = std::min(x + 1, srcWidth - 1);
            const int x_p2 = std::min(x + 2, srcWidth - 1);
 
            Kernel_4x4 ker; //perf: initialization is negligible
            ker.a = s_m1[x_m1]; //read sequentially from memory as far as possible
            ker.b = s_m1[x];
            ker.c = s_m1[x_p1];
            ker.d = s_m1[x_p2];
 
            ker.e = s_0[x_m1];
            ker.f = s_0[x];
            ker.g = s_0[x_p1];
            ker.h = s_0[x_p2];
 
            ker.i = s_p1[x_m1];
            ker.j = s_p1[x];
            ker.k = s_p1[x_p1];
            ker.l = s_p1[x_p2];
 
            ker.m = s_p2[x_m1];
            ker.n = s_p2[x];
            ker.o = s_p2[x_p1];
            ker.p = s_p2[x_p2];
 
            const BlendResult res = preProcessCorners(ker, cfg);
            /*
            preprocessing blend result:
            ---------
            | F | G |   //evaluate corner between F, G, J, K
            ----|---|   //input pixel is at position F
            | J | K |
            ---------
            */
            setTopR(preProcBuffer[x], res.blend_j);
 
            if (x + 1 < srcWidth)
                setTopL(preProcBuffer[x + 1], res.blend_k);
        }
    }
    //------------------------------------------------------------------------------------
 
    for (int y = yFirst; y < yLast; ++y)
    {
        uint32_t* out = trg + Scaler::scale * y * trgWidth; //consider MT "striped" access
 
        const uint32_t* s_m1 = src + srcWidth * std::max(y - 1, 0);
        const uint32_t* s_0  = src + srcWidth * y; //center line
        const uint32_t* s_p1 = src + srcWidth * std::min(y + 1, srcHeight - 1);
        const uint32_t* s_p2 = src + srcWidth * std::min(y + 2, srcHeight - 1);
 
        unsigned char blend_xy1 = 0; //corner blending for current (x, y + 1) position
 
        for (int x = 0; x < srcWidth; ++x, out += Scaler::scale)
        {
#ifndef NDEBUG
            breakIntoDebugger = debugPixelX == x && debugPixelY == y;
#endif
            //all those bounds checks have only insignificant impact on performance!
            const int x_m1 = std::max(x - 1, 0); //perf: prefer array indexing to additional pointers!
            const int x_p1 = std::min(x + 1, srcWidth - 1);
            const int x_p2 = std::min(x + 2, srcWidth - 1);
 
            //evaluate the four corners on bottom-right of current pixel
            unsigned char blend_xy = 0; //for current (x, y) position
            {
                Kernel_4x4 ker; //perf: initialization is negligible
                ker.a = s_m1[x_m1]; //read sequentially from memory as far as possible
                ker.b = s_m1[x];
                ker.c = s_m1[x_p1];
                ker.d = s_m1[x_p2];
 
                ker.e = s_0[x_m1];
                ker.f = s_0[x];
                ker.g = s_0[x_p1];
                ker.h = s_0[x_p2];
 
                ker.i = s_p1[x_m1];
                ker.j = s_p1[x];
                ker.k = s_p1[x_p1];
                ker.l = s_p1[x_p2];
 
                ker.m = s_p2[x_m1];
                ker.n = s_p2[x];
                ker.o = s_p2[x_p1];
                ker.p = s_p2[x_p2];
 
                const BlendResult res = preProcessCorners(ker, cfg);
                /*
                preprocessing blend result:
                ---------
                | F | G |   // evaluate corner between F, G, J, K
                ----|---|   // current input pixel is at position F
                | J | K |
                ---------
                */
                blend_xy = preProcBuffer[x];
                setBottomR(blend_xy, res.blend_f); //all four corners of (x, y) have been determined at this point due to processing sequence!
 
                setTopR(blend_xy1, res.blend_j); //set 2nd known corner for (x, y + 1)
                preProcBuffer[x] = blend_xy1; //store on current buffer position for use on next row
 
                blend_xy1 = 0;
                setTopL(blend_xy1, res.blend_k); //set 1st known corner for (x + 1, y + 1) and buffer for use on next column
 
                if (x + 1 < srcWidth) //set 3rd known corner for (x + 1, y)
                    setBottomL(preProcBuffer[x + 1], res.blend_g);
            }
 
            //fill block of size scale * scale with the given color
            fillBlock(out, trgWidth * sizeof(uint32_t), s_0[x], Scaler::scale); //place *after* preprocessing step, to not overwrite the results while processing the the last pixel!
 
            //blend four corners of current pixel
            if (blendingNeeded(blend_xy)) //good 20% perf-improvement
            {
                Kernel_3x3 ker; //perf: initialization is negligible
 
                ker.a = s_m1[x_m1]; //read sequentially from memory as far as possible
                ker.b = s_m1[x];
                ker.c = s_m1[x_p1];
 
                ker.d = s_0[x_m1];
                ker.e = s_0[x];
                ker.f = s_0[x_p1];
 
                ker.g = s_p1[x_m1];
                ker.h = s_p1[x];
                ker.i = s_p1[x_p1];
 
                scalePixel<Scaler, ROT_0  >(ker, out, trgWidth, blend_xy, cfg);
                scalePixel<Scaler, ROT_90 >(ker, out, trgWidth, blend_xy, cfg);
                scalePixel<Scaler, ROT_180>(ker, out, trgWidth, blend_xy, cfg);
                scalePixel<Scaler, ROT_270>(ker, out, trgWidth, blend_xy, cfg);
            }
        }
    }
}
 
 
struct Scaler2x
{
    static const int scale = 2;
 
    template <class OutputMatrix>
    static void blendLineShallow(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<scale - 1, 0>(), col);
        alphaBlend<3, 4>(out.template ref<scale - 1, 1>(), col);
    }
 
    template <class OutputMatrix>
    static void blendLineSteep(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<0, scale - 1>(), col);
        alphaBlend<3, 4>(out.template ref<1, scale - 1>(), col);
    }
 
    template <class OutputMatrix>
    static void blendLineSteepAndShallow(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<1, 0>(), col);
        alphaBlend<1, 4>(out.template ref<0, 1>(), col);
        alphaBlend<5, 6>(out.template ref<1, 1>(), col); //[!] fixes 7/8 used in xBR
    }
 
    template <class OutputMatrix>
    static void blendLineDiagonal(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 2>(out.template ref<1, 1>(), col);
    }
 
    template <class OutputMatrix>
    static void blendCorner(uint32_t col, OutputMatrix& out)
    {
        //model a round corner
        alphaBlend<21, 100>(out.template ref<1, 1>(), col); //exact: 1 - pi/4 = 0.2146018366
    }
};
 
 
struct Scaler3x
{
    static const int scale = 3;
 
    template <class OutputMatrix>
    static void blendLineShallow(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<scale - 1, 0>(), col);
        alphaBlend<1, 4>(out.template ref<scale - 2, 2>(), col);
 
        alphaBlend<3, 4>(out.template ref<scale - 1, 1>(), col);
        out.template ref<scale - 1, 2>() = col;
    }
 
    template <class OutputMatrix>
    static void blendLineSteep(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<0, scale - 1>(), col);
        alphaBlend<1, 4>(out.template ref<2, scale - 2>(), col);
 
        alphaBlend<3, 4>(out.template ref<1, scale - 1>(), col);
        out.template ref<2, scale - 1>() = col;
    }
 
    template <class OutputMatrix>
    static void blendLineSteepAndShallow(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<2, 0>(), col);
        alphaBlend<1, 4>(out.template ref<0, 2>(), col);
        alphaBlend<3, 4>(out.template ref<2, 1>(), col);
        alphaBlend<3, 4>(out.template ref<1, 2>(), col);
        out.template ref<2, 2>() = col;
    }
 
    template <class OutputMatrix>
    static void blendLineDiagonal(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 8>(out.template ref<1, 2>(), col);
        alphaBlend<1, 8>(out.template ref<2, 1>(), col);
        alphaBlend<7, 8>(out.template ref<2, 2>(), col);
    }
 
    template <class OutputMatrix>
    static void blendCorner(uint32_t col, OutputMatrix& out)
    {
        //model a round corner
        alphaBlend<45, 100>(out.template ref<2, 2>(), col); //exact: 0.4545939598
        //alphaBlend<14, 1000>(out.template ref<2, 1>(), col); //0.01413008627 -> negligible
        //alphaBlend<14, 1000>(out.template ref<1, 2>(), col); //0.01413008627
    }
};
 
 
struct Scaler4x
{
    static const int scale = 4;
 
    template <class OutputMatrix>
    static void blendLineShallow(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<scale - 1, 0>(), col);
        alphaBlend<1, 4>(out.template ref<scale - 2, 2>(), col);
 
        alphaBlend<3, 4>(out.template ref<scale - 1, 1>(), col);
        alphaBlend<3, 4>(out.template ref<scale - 2, 3>(), col);
 
        out.template ref<scale - 1, 2>() = col;
        out.template ref<scale - 1, 3>() = col;
    }
 
    template <class OutputMatrix>
    static void blendLineSteep(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<0, scale - 1>(), col);
        alphaBlend<1, 4>(out.template ref<2, scale - 2>(), col);
 
        alphaBlend<3, 4>(out.template ref<1, scale - 1>(), col);
        alphaBlend<3, 4>(out.template ref<3, scale - 2>(), col);
 
        out.template ref<2, scale - 1>() = col;
        out.template ref<3, scale - 1>() = col;
    }
 
    template <class OutputMatrix>
    static void blendLineSteepAndShallow(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<3, 4>(out.template ref<3, 1>(), col);
        alphaBlend<3, 4>(out.template ref<1, 3>(), col);
        alphaBlend<1, 4>(out.template ref<3, 0>(), col);
        alphaBlend<1, 4>(out.template ref<0, 3>(), col);
        alphaBlend<1, 3>(out.template ref<2, 2>(), col); //[!] fixes 1/4 used in xBR
        out.template ref<3, 3>() = out.template ref<3, 2>() = out.template ref<2, 3>() = col;
    }
 
    template <class OutputMatrix>
    static void blendLineDiagonal(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 2>(out.template ref<scale - 1, scale / 2    >(), col);
        alphaBlend<1, 2>(out.template ref<scale - 2, scale / 2 + 1>(), col);
        out.template ref<scale - 1, scale - 1>() = col;
    }
 
    template <class OutputMatrix>
    static void blendCorner(uint32_t col, OutputMatrix& out)
    {
        //model a round corner
        alphaBlend<68, 100>(out.template ref<3, 3>(), col); //exact: 0.6848532563
        alphaBlend< 9, 100>(out.template ref<3, 2>(), col); //0.08677704501
        alphaBlend< 9, 100>(out.template ref<2, 3>(), col); //0.08677704501
    }
};
 
 
struct Scaler5x
{
    static const int scale = 5;
 
    template <class OutputMatrix>
    static void blendLineShallow(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<scale - 1, 0>(), col);
        alphaBlend<1, 4>(out.template ref<scale - 2, 2>(), col);
        alphaBlend<1, 4>(out.template ref<scale - 3, 4>(), col);
 
        alphaBlend<3, 4>(out.template ref<scale - 1, 1>(), col);
        alphaBlend<3, 4>(out.template ref<scale - 2, 3>(), col);
 
        out.template ref<scale - 1, 2>() = col;
        out.template ref<scale - 1, 3>() = col;
        out.template ref<scale - 1, 4>() = col;
        out.template ref<scale - 2, 4>() = col;
    }
 
    template <class OutputMatrix>
    static void blendLineSteep(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<0, scale - 1>(), col);
        alphaBlend<1, 4>(out.template ref<2, scale - 2>(), col);
        alphaBlend<1, 4>(out.template ref<4, scale - 3>(), col);
 
        alphaBlend<3, 4>(out.template ref<1, scale - 1>(), col);
        alphaBlend<3, 4>(out.template ref<3, scale - 2>(), col);
 
        out.template ref<2, scale - 1>() = col;
        out.template ref<3, scale - 1>() = col;
        out.template ref<4, scale - 1>() = col;
        out.template ref<4, scale - 2>() = col;
    }
 
    template <class OutputMatrix>
    static void blendLineSteepAndShallow(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 4>(out.template ref<0, scale - 1>(), col);
        alphaBlend<1, 4>(out.template ref<2, scale - 2>(), col);
        alphaBlend<3, 4>(out.template ref<1, scale - 1>(), col);
 
        alphaBlend<1, 4>(out.template ref<scale - 1, 0>(), col);
        alphaBlend<1, 4>(out.template ref<scale - 2, 2>(), col);
        alphaBlend<3, 4>(out.template ref<scale - 1, 1>(), col);
 
        out.template ref<2, scale - 1>() = col;
        out.template ref<3, scale - 1>() = col;
 
        out.template ref<scale - 1, 2>() = col;
        out.template ref<scale - 1, 3>() = col;
 
        out.template ref<4, scale - 1>() = col;
 
        alphaBlend<2, 3>(out.template ref<3, 3>(), col);
    }
 
    template <class OutputMatrix>
    static void blendLineDiagonal(uint32_t col, OutputMatrix& out)
    {
        alphaBlend<1, 8>(out.template ref<scale - 1, scale / 2    >(), col);
        alphaBlend<1, 8>(out.template ref<scale - 2, scale / 2 + 1>(), col);
        alphaBlend<1, 8>(out.template ref<scale - 3, scale / 2 + 2>(), col);
 
        alphaBlend<7, 8>(out.template ref<4, 3>(), col);
        alphaBlend<7, 8>(out.template ref<3, 4>(), col);
 
        out.template ref<4, 4>() = col;
    }
 
    template <class OutputMatrix>
    static void blendCorner(uint32_t col, OutputMatrix& out)
    {
        //model a round corner
        alphaBlend<86, 100>(out.template ref<4, 4>(), col); //exact: 0.8631434088
        alphaBlend<23, 100>(out.template ref<4, 3>(), col); //0.2306749731
        alphaBlend<23, 100>(out.template ref<3, 4>(), col); //0.2306749731
        //alphaBlend<8, 1000>(out.template ref<4, 2>(), col); //0.008384061834 -> negligible
        //alphaBlend<8, 1000>(out.template ref<2, 4>(), col); //0.008384061834
    }
};
}
 
 
void xbrz::scale(size_t factor, const uint32_t* src, uint32_t* trg, int srcWidth, int srcHeight, const xbrz::ScalerCfg& cfg, int yFirst, int yLast)
{
    switch (factor)
    {
        case 2:
            return scaleImage<Scaler2x>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
        case 3:
            return scaleImage<Scaler3x>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
        case 4:
            return scaleImage<Scaler4x>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
        case 5:
            return scaleImage<Scaler5x>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
    }
    assert(false);
}
 
 
bool xbrz::equalColor(uint32_t col1, uint32_t col2, double luminanceWeight, double equalColorTolerance)
{
    return colorDist(col1, col2, luminanceWeight) < equalColorTolerance;
}
 
 
void xbrz::nearestNeighborScale(const uint32_t* src, int srcWidth, int srcHeight, int srcPitch,
                                uint32_t* trg, int trgWidth, int trgHeight, int trgPitch,
                                SliceType st, int yFirst, int yLast)
{
    if (srcPitch < srcWidth * static_cast<int>(sizeof(uint32_t))  ||
        trgPitch < trgWidth * static_cast<int>(sizeof(uint32_t)))
    {
        assert(false);
        return;
    }
 
    switch (st)
    {
        case NN_SCALE_SLICE_SOURCE:
            //nearest-neighbor (going over source image - fast for upscaling, since source is read only once
            yFirst = std::max(yFirst, 0);
            yLast  = std::min(yLast, srcHeight);
            if (yFirst >= yLast || trgWidth <= 0 || trgHeight <= 0) return;
 
            for (int y = yFirst; y < yLast; ++y)
            {
                //mathematically: ySrc = floor(srcHeight * yTrg / trgHeight)
                // => search for integers in: [ySrc, ySrc + 1) * trgHeight / srcHeight
 
                //keep within for loop to support MT input slices!
                const int yTrg_first = ( y      * trgHeight + srcHeight - 1) / srcHeight; //=ceil(y * trgHeight / srcHeight)
                const int yTrg_last  = ((y + 1) * trgHeight + srcHeight - 1) / srcHeight; //=ceil(((y + 1) * trgHeight) / srcHeight)
                const int blockHeight = yTrg_last - yTrg_first;
 
                if (blockHeight > 0)
                {
                    const uint32_t* srcLine = byteAdvance(src, y * srcPitch);
                    uint32_t* trgLine  = byteAdvance(trg, yTrg_first * trgPitch);
                    int xTrg_first = 0;
 
                    for (int x = 0; x < srcWidth; ++x)
                    {
                        int xTrg_last = ((x + 1) * trgWidth + srcWidth - 1) / srcWidth;
                        const int blockWidth = xTrg_last - xTrg_first;
                        if (blockWidth > 0)
                        {
                            xTrg_first = xTrg_last;
                            fillBlock(trgLine, trgPitch, srcLine[x], blockWidth, blockHeight);
                            trgLine += blockWidth;
                        }
                    }
                }
            }
            break;
 
        case NN_SCALE_SLICE_TARGET:
            //nearest-neighbor (going over target image - slow for upscaling, since source is read multiple times missing out on cache! Fast for similar image sizes!)
            yFirst = std::max(yFirst, 0);
            yLast  = std::min(yLast, trgHeight);
            if (yFirst >= yLast || srcHeight <= 0 || srcWidth <= 0) return;
 
            for (int y = yFirst; y < yLast; ++y)
            {
                uint32_t* trgLine = byteAdvance(trg, y * trgPitch);
                const int ySrc = srcHeight * y / trgHeight;
                const uint32_t* srcLine = byteAdvance(src, ySrc * srcPitch);
                for (int x = 0; x < trgWidth; ++x)
                {
                    const int xSrc = srcWidth * x / trgWidth;
                    trgLine[x] = srcLine[xSrc];
                }
            }
            break;
    }
}