10.0

1 files changed, 1262 insertions, 0 deletions

diff --git a/xBRZ/src/xbrz.cpp b/xBRZ/src/xbrz.cpp
new file mode 100755
index 00000000..4d3ccd25
--- /dev/null
+++ b/xBRZ/src/xbrz.cpp
@@ -0,0 +1,1262 @@
+// ****************************************************************************
+// * This file is part of the xBRZ project. It is distributed under           *
+// * GNU General Public License: https://www.gnu.org/licenses/gpl-3.0         *
+// * 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 following libraries            *
+// * (or with modified versions that use the same licenses), and distribute   *
+// * linked combinations including the two: MAME, FreeFileSync, Snes9x, ePSXe *
+// * You must obey the GNU General Public License in all respects for all of  *
+// * the code used other than MAME, FreeFileSync, Snes9x, ePSXe.              *
+// * 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.h"
+#include <cassert>
+#include <vector>
+#include <algorithm>
+#include <cmath> //std::sqrt
+#include "xbrz_tools.h"
+
+using namespace xbrz;
+
+
+namespace
+{
+template <unsigned int M, unsigned int N> inline
+uint32_t gradientRGB(uint32_t pixFront, uint32_t pixBack) //blend front color with opacity M / N over opaque background: http://en.wikipedia.org/wiki/Alpha_compositing#Alpha_blending
+{
+    static_assert(0 < M && M < N && N <= 1000, "");
+
+    auto calcColor = [](unsigned char colFront, unsigned char colBack) -> unsigned char { return (colFront * M + colBack * (N - M)) / N; };
+
+    return makePixel(calcColor(getRed  (pixFront), getRed  (pixBack)),
+                     calcColor(getGreen(pixFront), getGreen(pixBack)),
+                     calcColor(getBlue (pixFront), getBlue (pixBack)));
+}
+
+
+template <unsigned int M, unsigned int N> inline
+uint32_t gradientARGB(uint32_t pixFront, uint32_t pixBack) //find intermediate color between two colors with alpha channels (=> NO alpha blending!!!)
+{
+    static_assert(0 < M && M < N && N <= 1000, "");
+
+    const unsigned int weightFront = getAlpha(pixFront) * M;
+    const unsigned int weightBack  = getAlpha(pixBack) * (N - M);
+    const unsigned int weightSum   = weightFront + weightBack;
+    if (weightSum == 0)
+        return 0;
+
+    auto calcColor = [=](unsigned char colFront, unsigned char colBack)
+    {
+        return static_cast<unsigned char>((colFront * weightFront + colBack * weightBack) / weightSum);
+    };
+
+    return makePixel(static_cast<unsigned char>(weightSum / N),
+                     calcColor(getRed  (pixFront), getRed  (pixBack)),
+                     calcColor(getGreen(pixFront), getGreen(pixBack)),
+                     calcColor(getBlue (pixFront), getBlue (pixBack)));
+}
+
+
+//inline
+//double fastSqrt(double n)
+//{
+//    __asm //speeds up xBRZ by about 9% compared to std::sqrt which internally uses the same assembler instructions but adds some "fluff"
+//    {
+//        fld n
+//        fsqrt
+//    }
+//}
+//
+
+
+#if   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; }
+
+
+#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
+
+
+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); //substraction 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_b = 0.0593; //ITU-R BT.2020 conversion
+    const double k_r = 0.2627; //
+    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));
+}
+
+
+inline
+double distYCbCrBuffered(uint32_t pix1, uint32_t pix2)
+{
+    //30% perf boost compared to plain distYCbCr()!
+    //consumes 64 MB memory; using double is only 2% faster, but takes 128 MB
+    static const std::vector<float> diffToDist = []
+    {
+        std::vector<float> tmp;
+
+        for (uint32_t i = 0; i < 256 * 256 * 256; ++i) //startup time: 114 ms on Intel Core i5 (four cores)
+        {
+            const int r_diff = static_cast<signed char>(getByte<2>(i)) * 2;
+            const int g_diff = static_cast<signed char>(getByte<1>(i)) * 2;
+            const int b_diff = static_cast<signed char>(getByte<0>(i)) * 2;
+
+            const double k_b = 0.0593; //ITU-R BT.2020 conversion
+            const double k_r = 0.2627; //
+            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);
+
+            tmp.push_back(static_cast<float>(std::sqrt(square(y) + square(c_b) + square(c_r))));
+        }
+        return tmp;
+    }();
+
+    //if (pix1 == pix2) -> 8% perf degradation!
+    //    return 0;
+    //if (pix1 < pix2)
+    //    std::swap(pix1, pix2); -> 30% perf degradation!!!
+
+    const int r_diff = static_cast<int>(getRed  (pix1)) - getRed  (pix2);
+    const int g_diff = static_cast<int>(getGreen(pix1)) - getGreen(pix2);
+    const int b_diff = static_cast<int>(getBlue (pix1)) - getBlue (pix2);
+
+    const size_t index = (static_cast<unsigned char>(r_diff / 2) << 16) | //slightly reduce precision (division by 2) to squeeze value into single byte
+                         (static_cast<unsigned char>(g_diff / 2) <<  8) |
+                         (static_cast<unsigned char>(b_diff / 2));
+
+#if 0 //attention: the following calculation creates an asymmetric color distance!!! (e.g. r_diff=46 will be unpacked as 45, but r_diff=-46 unpacks to -47
+    const size_t index = (((r_diff + 0xFF) / 2) << 16) | //slightly reduce precision (division by 2) to squeeze value into single byte
+                         (((g_diff + 0xFF) / 2) <<  8) |
+                         (( b_diff + 0xFF) / 2);
+#endif
+    return diffToDist[index];
+}
+
+
+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;
+};
+
+
+struct Kernel_4x4 //kernel for preprocessing step
+{
+    uint32_t
+    /**/a, b, c, d,
+    /**/e, f, g, h,
+    /**/i, j, k, l,
+    /**/m, n, o, p;
+};
+
+/*
+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 |
+-----------------
+*/
+template <class ColorDistance>
+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 = [&](uint32_t pix1, uint32_t pix2) { return ColorDistance::dist(pix1, pix2, cfg.luminanceWeight); };
+
+    double jg = dist(ker.i, ker.f) + dist(ker.f, ker.c) + dist(ker.n, ker.k) + dist(ker.k, ker.h) + cfg.centerDirectionBias * 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) + cfg.centerDirectionBias * 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,  b,  c,
+    /**/d,  e,  f,
+    /**/g,  h,  i;
+};
+
+#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; }
+
+
+
+
+/*
+input kernel area naming convention:
+-------------
+| A | B | C |
+----|---|---|
+| D | E | F | //input pixel is at position E
+----|---|---|
+| G | H | I |
+-------------
+*/
+template <class Scaler, class ColorDistance, RotationDegree rotDeg>
+FORCE_INLINE //perf: quite worth it!
+void blendPixel(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)
+
+
+    (void)a; //silence Clang's -Wunused-function
+
+    const unsigned char blend = rotateBlendInfo<rotDeg>(blendInfo);
+
+    if (getBottomR(blend) >= BLEND_NORMAL)
+    {
+        auto eq   = [&](uint32_t pix1, uint32_t pix2) { return ColorDistance::dist(pix1, pix2, cfg.luminanceWeight) < cfg.equalColorTolerance; };
+        auto dist = [&](uint32_t pix1, uint32_t pix2) { return ColorDistance::dist(pix1, pix2, cfg.luminanceWeight); };
+
+        const bool doLineBlend = [&]() -> bool
+        {
+            if (getBottomR(blend) >= BLEND_DOMINANT)
+                return true;
+
+            //make sure there is no second blending in an adjacent rotation for this pixel: handles insular pixels, mario eyes
+            if (getTopR(blend) != BLEND_NONE && !eq(e, g)) //but support double-blending for 90° corners
+                return false;
+            if (getBottomL(blend) != BLEND_NONE && !eq(e, c))
+                return false;
+
+            //no full blending for L-shapes; blend corner only (handles "mario mushroom eyes")
+            if (!eq(e, i) && eq(g, h) && eq(h, i) && eq(i, f) && eq(f, c))
+                return false;
+
+            return true;
+        }();
+
+        const uint32_t px = dist(e, f) <= dist(e, h) ? f : h; //choose most similar color
+
+        OutputMatrix<Scaler::scale, rotDeg> out(target, trgWidth);
+
+        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, class ColorDistance> //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, '\0');
+    static_assert(BLEND_NONE == 0, "");
+
+    //initialize preprocessing buffer for first row of current stripe: 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<ColorDistance>(ker, cfg);
+            /*
+            preprocessing blend result:
+            ---------
+            | F | G |   //evalute corner between F, G, J, K
+            ----|---|   //input pixel is at position F
+            | J | K |
+            ---------
+            */
+            setTopR(preProcBuffer[x], res.blend_j);
+
+            if (x + 1 < bufferSize)
+                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)
+        {
+            //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);
+
+            Kernel_4x4 ker4 = {}; //perf: initialization is negligible
+
+            ker4.a = s_m1[x_m1]; //read sequentially from memory as far as possible
+            ker4.b = s_m1[x];
+            ker4.c = s_m1[x_p1];
+            ker4.d = s_m1[x_p2];
+
+            ker4.e = s_0[x_m1];
+            ker4.f = s_0[x];
+            ker4.g = s_0[x_p1];
+            ker4.h = s_0[x_p2];
+
+            ker4.i = s_p1[x_m1];
+            ker4.j = s_p1[x];
+            ker4.k = s_p1[x_p1];
+            ker4.l = s_p1[x_p2];
+
+            ker4.m = s_p2[x_m1];
+            ker4.n = s_p2[x];
+            ker4.o = s_p2[x_p1];
+            ker4.p = s_p2[x_p2];
+
+            //evaluate the four corners on bottom-right of current pixel
+            unsigned char blend_xy = 0; //for current (x, y) position
+            {
+                const BlendResult res = preProcessCorners<ColorDistance>(ker4, cfg);
+                /*
+                preprocessing blend result:
+                ---------
+                | F | G |   //evalute 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 < bufferSize) //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), ker4.f, Scaler::scale, 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 5% perf-improvement
+            {
+                Kernel_3x3 ker3 = {}; //perf: initialization is negligible
+
+                ker3.a = ker4.a;
+                ker3.b = ker4.b;
+                ker3.c = ker4.c;
+
+                ker3.d = ker4.e;
+                ker3.e = ker4.f;
+                ker3.f = ker4.g;
+
+                ker3.g = ker4.i;
+                ker3.h = ker4.j;
+                ker3.i = ker4.k;
+
+                blendPixel<Scaler, ColorDistance, ROT_0  >(ker3, out, trgWidth, blend_xy, cfg);
+                blendPixel<Scaler, ColorDistance, ROT_90 >(ker3, out, trgWidth, blend_xy, cfg);
+                blendPixel<Scaler, ColorDistance, ROT_180>(ker3, out, trgWidth, blend_xy, cfg);
+                blendPixel<Scaler, ColorDistance, ROT_270>(ker3, out, trgWidth, blend_xy, cfg);
+            }
+        }
+    }
+}
+
+//------------------------------------------------------------------------------------
+
+template <class ColorGradient>
+struct Scaler2x : public ColorGradient
+{
+    static const int scale = 2;
+
+    template <unsigned int M, unsigned int N> //bring template function into scope for GCC
+    static void alphaGrad(uint32_t& pixBack, uint32_t pixFront) { ColorGradient::template alphaGrad<M, N>(pixBack, pixFront); }
+
+
+    template <class OutputMatrix>
+    static void blendLineShallow(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 4>(out.template ref<scale - 1, 0>(), col);
+        alphaGrad<3, 4>(out.template ref<scale - 1, 1>(), col);
+    }
+
+    template <class OutputMatrix>
+    static void blendLineSteep(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 4>(out.template ref<0, scale - 1>(), col);
+        alphaGrad<3, 4>(out.template ref<1, scale - 1>(), col);
+    }
+
+    template <class OutputMatrix>
+    static void blendLineSteepAndShallow(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 4>(out.template ref<1, 0>(), col);
+        alphaGrad<1, 4>(out.template ref<0, 1>(), col);
+        alphaGrad<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)
+    {
+        alphaGrad<1, 2>(out.template ref<1, 1>(), col);
+    }
+
+    template <class OutputMatrix>
+    static void blendCorner(uint32_t col, OutputMatrix& out)
+    {
+        //model a round corner
+        alphaGrad<21, 100>(out.template ref<1, 1>(), col); //exact: 1 - pi/4 = 0.2146018366
+    }
+};
+
+
+template <class ColorGradient>
+struct Scaler3x : public ColorGradient
+{
+    static const int scale = 3;
+
+    template <unsigned int M, unsigned int N> //bring template function into scope for GCC
+    static void alphaGrad(uint32_t& pixBack, uint32_t pixFront) { ColorGradient::template alphaGrad<M, N>(pixBack, pixFront); }
+
+
+    template <class OutputMatrix>
+    static void blendLineShallow(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 4>(out.template ref<scale - 1, 0>(), col);
+        alphaGrad<1, 4>(out.template ref<scale - 2, 2>(), col);
+
+        alphaGrad<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)
+    {
+        alphaGrad<1, 4>(out.template ref<0, scale - 1>(), col);
+        alphaGrad<1, 4>(out.template ref<2, scale - 2>(), col);
+
+        alphaGrad<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)
+    {
+        alphaGrad<1, 4>(out.template ref<2, 0>(), col);
+        alphaGrad<1, 4>(out.template ref<0, 2>(), col);
+        alphaGrad<3, 4>(out.template ref<2, 1>(), col);
+        alphaGrad<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)
+    {
+        alphaGrad<1, 8>(out.template ref<1, 2>(), col); //conflict with other rotations for this odd scale
+        alphaGrad<1, 8>(out.template ref<2, 1>(), col);
+        alphaGrad<7, 8>(out.template ref<2, 2>(), col); //
+    }
+
+    template <class OutputMatrix>
+    static void blendCorner(uint32_t col, OutputMatrix& out)
+    {
+        //model a round corner
+        alphaGrad<45, 100>(out.template ref<2, 2>(), col); //exact: 0.4545939598
+        //alphaGrad<7, 256>(out.template ref<2, 1>(), col); //0.02826017254 -> negligible + avoid conflicts with other rotations for this odd scale
+        //alphaGrad<7, 256>(out.template ref<1, 2>(), col); //0.02826017254
+    }
+};
+
+
+template <class ColorGradient>
+struct Scaler4x : public ColorGradient
+{
+    static const int scale = 4;
+
+    template <unsigned int M, unsigned int N> //bring template function into scope for GCC
+    static void alphaGrad(uint32_t& pixBack, uint32_t pixFront) { ColorGradient::template alphaGrad<M, N>(pixBack, pixFront); }
+
+
+    template <class OutputMatrix>
+    static void blendLineShallow(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 4>(out.template ref<scale - 1, 0>(), col);
+        alphaGrad<1, 4>(out.template ref<scale - 2, 2>(), col);
+
+        alphaGrad<3, 4>(out.template ref<scale - 1, 1>(), col);
+        alphaGrad<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)
+    {
+        alphaGrad<1, 4>(out.template ref<0, scale - 1>(), col);
+        alphaGrad<1, 4>(out.template ref<2, scale - 2>(), col);
+
+        alphaGrad<3, 4>(out.template ref<1, scale - 1>(), col);
+        alphaGrad<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)
+    {
+        alphaGrad<3, 4>(out.template ref<3, 1>(), col);
+        alphaGrad<3, 4>(out.template ref<1, 3>(), col);
+        alphaGrad<1, 4>(out.template ref<3, 0>(), col);
+        alphaGrad<1, 4>(out.template ref<0, 3>(), col);
+
+        alphaGrad<1, 3>(out.template ref<2, 2>(), col); //[!] fixes 1/4 used in xBR
+
+        out.template ref<3, 3>() = col;
+        out.template ref<3, 2>() = col;
+        out.template ref<2, 3>() = col;
+    }
+
+    template <class OutputMatrix>
+    static void blendLineDiagonal(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 2>(out.template ref<scale - 1, scale / 2    >(), col);
+        alphaGrad<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
+        alphaGrad<68, 100>(out.template ref<3, 3>(), col); //exact: 0.6848532563
+        alphaGrad< 9, 100>(out.template ref<3, 2>(), col); //0.08677704501
+        alphaGrad< 9, 100>(out.template ref<2, 3>(), col); //0.08677704501
+    }
+};
+
+
+template <class ColorGradient>
+struct Scaler5x : public ColorGradient
+{
+    static const int scale = 5;
+
+    template <unsigned int M, unsigned int N> //bring template function into scope for GCC
+    static void alphaGrad(uint32_t& pixBack, uint32_t pixFront) { ColorGradient::template alphaGrad<M, N>(pixBack, pixFront); }
+
+
+    template <class OutputMatrix>
+    static void blendLineShallow(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 4>(out.template ref<scale - 1, 0>(), col);
+        alphaGrad<1, 4>(out.template ref<scale - 2, 2>(), col);
+        alphaGrad<1, 4>(out.template ref<scale - 3, 4>(), col);
+
+        alphaGrad<3, 4>(out.template ref<scale - 1, 1>(), col);
+        alphaGrad<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)
+    {
+        alphaGrad<1, 4>(out.template ref<0, scale - 1>(), col);
+        alphaGrad<1, 4>(out.template ref<2, scale - 2>(), col);
+        alphaGrad<1, 4>(out.template ref<4, scale - 3>(), col);
+
+        alphaGrad<3, 4>(out.template ref<1, scale - 1>(), col);
+        alphaGrad<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)
+    {
+        alphaGrad<1, 4>(out.template ref<0, scale - 1>(), col);
+        alphaGrad<1, 4>(out.template ref<2, scale - 2>(), col);
+        alphaGrad<3, 4>(out.template ref<1, scale - 1>(), col);
+
+        alphaGrad<1, 4>(out.template ref<scale - 1, 0>(), col);
+        alphaGrad<1, 4>(out.template ref<scale - 2, 2>(), col);
+        alphaGrad<3, 4>(out.template ref<scale - 1, 1>(), col);
+
+        alphaGrad<2, 3>(out.template ref<3, 3>(), 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<scale - 1, 2>() = col;
+        out.template ref<scale - 1, 3>() = col;
+    }
+
+    template <class OutputMatrix>
+    static void blendLineDiagonal(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 8>(out.template ref<scale - 1, scale / 2    >(), col); //conflict with other rotations for this odd scale
+        alphaGrad<1, 8>(out.template ref<scale - 2, scale / 2 + 1>(), col);
+        alphaGrad<1, 8>(out.template ref<scale - 3, scale / 2 + 2>(), col); //
+
+        alphaGrad<7, 8>(out.template ref<4, 3>(), col);
+        alphaGrad<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
+        alphaGrad<86, 100>(out.template ref<4, 4>(), col); //exact: 0.8631434088
+        alphaGrad<23, 100>(out.template ref<4, 3>(), col); //0.2306749731
+        alphaGrad<23, 100>(out.template ref<3, 4>(), col); //0.2306749731
+        //alphaGrad<1, 64>(out.template ref<4, 2>(), col); //0.01676812367 -> negligible + avoid conflicts with other rotations for this odd scale
+        //alphaGrad<1, 64>(out.template ref<2, 4>(), col); //0.01676812367
+    }
+};
+
+
+template <class ColorGradient>
+struct Scaler6x : public ColorGradient
+{
+    static const int scale = 6;
+
+    template <unsigned int M, unsigned int N> //bring template function into scope for GCC
+    static void alphaGrad(uint32_t& pixBack, uint32_t pixFront) { ColorGradient::template alphaGrad<M, N>(pixBack, pixFront); }
+
+
+    template <class OutputMatrix>
+    static void blendLineShallow(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 4>(out.template ref<scale - 1, 0>(), col);
+        alphaGrad<1, 4>(out.template ref<scale - 2, 2>(), col);
+        alphaGrad<1, 4>(out.template ref<scale - 3, 4>(), col);
+
+        alphaGrad<3, 4>(out.template ref<scale - 1, 1>(), col);
+        alphaGrad<3, 4>(out.template ref<scale - 2, 3>(), col);
+        alphaGrad<3, 4>(out.template ref<scale - 3, 5>(), 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 - 1, 5>() = col;
+
+        out.template ref<scale - 2, 4>() = col;
+        out.template ref<scale - 2, 5>() = col;
+    }
+
+    template <class OutputMatrix>
+    static void blendLineSteep(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 4>(out.template ref<0, scale - 1>(), col);
+        alphaGrad<1, 4>(out.template ref<2, scale - 2>(), col);
+        alphaGrad<1, 4>(out.template ref<4, scale - 3>(), col);
+
+        alphaGrad<3, 4>(out.template ref<1, scale - 1>(), col);
+        alphaGrad<3, 4>(out.template ref<3, scale - 2>(), col);
+        alphaGrad<3, 4>(out.template ref<5, scale - 3>(), 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<5, scale - 1>() = col;
+
+        out.template ref<4, scale - 2>() = col;
+        out.template ref<5, scale - 2>() = col;
+    }
+
+    template <class OutputMatrix>
+    static void blendLineSteepAndShallow(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 4>(out.template ref<0, scale - 1>(), col);
+        alphaGrad<1, 4>(out.template ref<2, scale - 2>(), col);
+        alphaGrad<3, 4>(out.template ref<1, scale - 1>(), col);
+        alphaGrad<3, 4>(out.template ref<3, scale - 2>(), col);
+
+        alphaGrad<1, 4>(out.template ref<scale - 1, 0>(), col);
+        alphaGrad<1, 4>(out.template ref<scale - 2, 2>(), col);
+        alphaGrad<3, 4>(out.template ref<scale - 1, 1>(), col);
+        alphaGrad<3, 4>(out.template ref<scale - 2, 3>(), 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<5, scale - 1>() = col;
+
+        out.template ref<4, scale - 2>() = col;
+        out.template ref<5, scale - 2>() = col;
+
+        out.template ref<scale - 1, 2>() = col;
+        out.template ref<scale - 1, 3>() = col;
+    }
+
+    template <class OutputMatrix>
+    static void blendLineDiagonal(uint32_t col, OutputMatrix& out)
+    {
+        alphaGrad<1, 2>(out.template ref<scale - 1, scale / 2    >(), col);
+        alphaGrad<1, 2>(out.template ref<scale - 2, scale / 2 + 1>(), col);
+        alphaGrad<1, 2>(out.template ref<scale - 3, scale / 2 + 2>(), col);
+
+        out.template ref<scale - 2, scale - 1>() = col;
+        out.template ref<scale - 1, scale - 1>() = col;
+        out.template ref<scale - 1, scale - 2>() = col;
+    }
+
+    template <class OutputMatrix>
+    static void blendCorner(uint32_t col, OutputMatrix& out)
+    {
+        //model a round corner
+        alphaGrad<97, 100>(out.template ref<5, 5>(), col); //exact: 0.9711013910
+        alphaGrad<42, 100>(out.template ref<4, 5>(), col); //0.4236372243
+        alphaGrad<42, 100>(out.template ref<5, 4>(), col); //0.4236372243
+        alphaGrad< 6, 100>(out.template ref<5, 3>(), col); //0.05652034508
+        alphaGrad< 6, 100>(out.template ref<3, 5>(), col); //0.05652034508
+    }
+};
+
+//------------------------------------------------------------------------------------
+
+struct ColorDistanceRGB
+{
+    static double dist(uint32_t pix1, uint32_t pix2, double luminanceWeight)
+    {
+        return distYCbCrBuffered(pix1, pix2);
+
+        //if (pix1 == pix2) //about 4% perf boost
+        //    return 0;
+        //return distYCbCr(pix1, pix2, luminanceWeight);
+    }
+};
+
+struct ColorDistanceARGB
+{
+    static double dist(uint32_t pix1, uint32_t pix2, double luminanceWeight)
+    {
+        const double a1 = getAlpha(pix1) / 255.0 ;
+        const double a2 = getAlpha(pix2) / 255.0 ;
+        /*
+        Requirements for a color distance handling alpha channel: with a1, a2 in [0, 1]
+
+            1. if a1 = a2, distance should be: a1 * distYCbCr()
+            2. if a1 = 0,  distance should be: a2 * distYCbCr(black, white) = a2 * 255
+            3. if a1 = 1,  ??? maybe: 255 * (1 - a2) + a2 * distYCbCr()
+        */
+
+        //return std::min(a1, a2) * distYCbCrBuffered(pix1, pix2) + 255 * abs(a1 - a2);
+        //=> following code is 15% faster:
+        const double d = distYCbCrBuffered(pix1, pix2);
+        if (a1 < a2)
+            return a1 * d + 255 * (a2 - a1);
+        else
+            return a2 * d + 255 * (a1 - a2);
+
+        //alternative? return std::sqrt(a1 * a2 * square(distYCbCrBuffered(pix1, pix2)) + square(255 * (a1 - a2)));
+    }
+};
+
+
+struct ColorDistanceUnbufferedARGB
+{
+    static double dist(uint32_t pix1, uint32_t pix2, double luminanceWeight)
+    {
+        const double a1 = getAlpha(pix1) / 255.0 ;
+        const double a2 = getAlpha(pix2) / 255.0 ;
+
+        const double d = distYCbCr(pix1, pix2, luminanceWeight);
+        if (a1 < a2)
+            return a1 * d + 255 * (a2 - a1);
+        else
+            return a2 * d + 255 * (a1 - a2);
+    }
+};
+
+
+struct ColorGradientRGB
+{
+    template <unsigned int M, unsigned int N>
+    static void alphaGrad(uint32_t& pixBack, uint32_t pixFront)
+    {
+        pixBack = gradientRGB<M, N>(pixFront, pixBack);
+    }
+};
+
+struct ColorGradientARGB
+{
+    template <unsigned int M, unsigned int N>
+    static void alphaGrad(uint32_t& pixBack, uint32_t pixFront)
+    {
+        pixBack = gradientARGB<M, N>(pixFront, pixBack);
+    }
+};
+}
+
+
+void xbrz::scale(size_t factor, const uint32_t* src, uint32_t* trg, int srcWidth, int srcHeight, ColorFormat colFmt, const xbrz::ScalerCfg& cfg, int yFirst, int yLast)
+{
+if (factor == 1)
+	{
+		std::copy(src + yFirst * srcWidth, src + yLast * srcWidth, trg);
+		return;
+	}
+
+    static_assert(SCALE_FACTOR_MAX == 6, "");
+    switch (colFmt)
+    {
+        case ColorFormat::RGB:
+            switch (factor)
+            {
+                case 2:
+                    return scaleImage<Scaler2x<ColorGradientRGB>, ColorDistanceRGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 3:
+                    return scaleImage<Scaler3x<ColorGradientRGB>, ColorDistanceRGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 4:
+                    return scaleImage<Scaler4x<ColorGradientRGB>, ColorDistanceRGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 5:
+                    return scaleImage<Scaler5x<ColorGradientRGB>, ColorDistanceRGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 6:
+                    return scaleImage<Scaler6x<ColorGradientRGB>, ColorDistanceRGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+            }
+            break;
+
+        case ColorFormat::ARGB:
+            switch (factor)
+            {
+                case 2:
+                    return scaleImage<Scaler2x<ColorGradientARGB>, ColorDistanceARGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 3:
+                    return scaleImage<Scaler3x<ColorGradientARGB>, ColorDistanceARGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 4:
+                    return scaleImage<Scaler4x<ColorGradientARGB>, ColorDistanceARGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 5:
+                    return scaleImage<Scaler5x<ColorGradientARGB>, ColorDistanceARGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 6:
+                    return scaleImage<Scaler6x<ColorGradientARGB>, ColorDistanceARGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+            }
+            break;
+
+        case ColorFormat::ARGB_UNBUFFERED:
+            switch (factor)
+            {
+                case 2:
+                    return scaleImage<Scaler2x<ColorGradientARGB>, ColorDistanceUnbufferedARGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 3:
+                    return scaleImage<Scaler3x<ColorGradientARGB>, ColorDistanceUnbufferedARGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 4:
+                    return scaleImage<Scaler4x<ColorGradientARGB>, ColorDistanceUnbufferedARGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 5:
+                    return scaleImage<Scaler5x<ColorGradientARGB>, ColorDistanceUnbufferedARGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+                case 6:
+                    return scaleImage<Scaler6x<ColorGradientARGB>, ColorDistanceUnbufferedARGB>(src, trg, srcWidth, srcHeight, cfg, yFirst, yLast);
+            }
+            break;
+    }
+    assert(false);
+}
+
+
+bool xbrz::equalColorTest(uint32_t col1, uint32_t col2, ColorFormat colFmt, double luminanceWeight, double equalColorTolerance)
+{
+    switch (colFmt)
+    {
+        case ColorFormat::RGB:
+            return ColorDistanceRGB::dist(col1, col2, luminanceWeight) < equalColorTolerance;
+        case ColorFormat::ARGB:
+            return ColorDistanceARGB::dist(col1, col2, luminanceWeight) < equalColorTolerance;
+        case ColorFormat::ARGB_UNBUFFERED:
+            return ColorDistanceUnbufferedARGB::dist(col1, col2, luminanceWeight) < equalColorTolerance;
+    }
+    assert(false);
+    return false;
+}
+
+
+void xbrz::bilinearScale(const uint32_t* src, int srcWidth, int srcHeight,
+                         /**/  uint32_t* trg, int trgWidth, int trgHeight)
+{
+    bilinearScale(src, srcWidth, srcHeight, srcWidth * sizeof(uint32_t),
+                  trg, trgWidth, trgHeight, trgWidth * sizeof(uint32_t),
+    0, trgHeight, [](uint32_t pix) { return pix; });
+}
+
+
+void xbrz::nearestNeighborScale(const uint32_t* src, int srcWidth, int srcHeight,
+                                /**/  uint32_t* trg, int trgWidth, int trgHeight)
+{
+    nearestNeighborScale(src, srcWidth, srcHeight, srcWidth * sizeof(uint32_t),
+                         trg, trgWidth, trgHeight, trgWidth * sizeof(uint32_t),
+    0, trgHeight, [](uint32_t pix) { return pix; });
+}
+
+
+#if 0
+//#include <ppl.h>
+void bilinearScaleCpu(const uint32_t* src, int srcWidth, int srcHeight,
+                      /**/  uint32_t* trg, int trgWidth, int trgHeight)
+{
+    const int TASK_GRANULARITY = 16;
+
+    concurrency::task_group tg;
+
+    for (int i = 0; i < trgHeight; i += TASK_GRANULARITY)
+        tg.run([=]
+    {
+        const int iLast = std::min(i + TASK_GRANULARITY, trgHeight);
+        xbrz::bilinearScale(src, srcWidth, srcHeight, srcWidth * sizeof(uint32_t),
+                            trg, trgWidth, trgHeight, trgWidth * sizeof(uint32_t),
+        i, iLast, [](uint32_t pix) { return pix; });
+    });
+    tg.wait();
+}
+
+
+//Perf: AMP vs CPU: merely ~10% shorter runtime (scaling 1280x800 -> 1920x1080)
+//#include <amp.h>
+void bilinearScaleAmp(const uint32_t* src, int srcWidth, int srcHeight, //throw concurrency::runtime_exception
+                      /**/  uint32_t* trg, int trgWidth, int trgHeight)
+{
+    //C++ AMP reference:       https://msdn.microsoft.com/en-us/library/hh289390.aspx
+    //introduction to C++ AMP: https://msdn.microsoft.com/en-us/magazine/hh882446.aspx
+    using namespace concurrency;
+    //TODO: pitch
+
+    if (srcHeight <= 0 || srcWidth <= 0) return;
+
+    const float scaleX = static_cast<float>(trgWidth ) / srcWidth;
+    const float scaleY = static_cast<float>(trgHeight) / srcHeight;
+
+    array_view<const uint32_t, 2> srcView(srcHeight, srcWidth, src);
+    array_view<      uint32_t, 2> trgView(trgHeight, trgWidth, trg);
+    trgView.discard_data();
+
+    parallel_for_each(trgView.extent, [=](index<2> idx) restrict(amp) //throw ?
+    {
+        const int y = idx[0];
+        const int x = idx[1];
+        //Perf notes:
+        //    -> float-based calculation is (almost) 2x as fas as double!
+        //    -> no noticeable improvement via tiling: https://msdn.microsoft.com/en-us/magazine/hh882447.aspx
+        //    -> no noticeable improvement with restrict(amp,cpu)
+        //    -> iterating over y-axis only is significantly slower!
+        //    -> pre-calculating x,y-dependent variables in a buffer + array_view<> is ~ 20 % slower!
+        const int y1 = srcHeight * y / trgHeight;
+        int y2 = y1 + 1;
+        if (y2 == srcHeight) --y2;
+
+        const float yy1 = y / scaleY - y1;
+        const float y2y = 1 - yy1;
+        //-------------------------------------
+        const int x1 = srcWidth * x / trgWidth;
+        int x2 = x1 + 1;
+        if (x2 == srcWidth) --x2;
+
+        const float xx1 = x / scaleX - x1;
+        const float x2x = 1 - xx1;
+        //-------------------------------------
+        const float x2xy2y = x2x * y2y;
+        const float xx1y2y = xx1 * y2y;
+        const float x2xyy1 = x2x * yy1;
+        const float xx1yy1 = xx1 * yy1;
+
+        auto interpolate = [=](int offset)
+        {
+            /*
+                https://en.wikipedia.org/wiki/Bilinear_interpolation
+                (c11(x2 - x) + c21(x - x1)) * (y2 - y ) +
+                (c12(x2 - x) + c22(x - x1)) * (y  - y1)
+            */
+            const auto c11 = (srcView(y1, x1) >> (8 * offset)) & 0xff;
+            const auto c21 = (srcView(y1, x2) >> (8 * offset)) & 0xff;
+            const auto c12 = (srcView(y2, x1) >> (8 * offset)) & 0xff;
+            const auto c22 = (srcView(y2, x2) >> (8 * offset)) & 0xff;
+
+            return c11 * x2xy2y + c21 * xx1y2y +
+                   c12 * x2xyy1 + c22 * xx1yy1;
+        };
+
+        const float bi = interpolate(0);
+        const float gi = interpolate(1);
+        const float ri = interpolate(2);
+        const float ai = interpolate(3);
+
+        const auto b = static_cast<uint32_t>(bi + 0.5f);
+        const auto g = static_cast<uint32_t>(gi + 0.5f);
+        const auto r = static_cast<uint32_t>(ri + 0.5f);
+        const auto a = static_cast<uint32_t>(ai + 0.5f);
+
+        trgView(y, x) = (a << 24) | (r << 16) | (g << 8) | b;
+    });
+    trgView.synchronize(); //throw ?
+}
+#endif