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      1 /*
      2  * Copyright 2015 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 #ifndef Sk4pxXfermode_DEFINED
      9 #define Sk4pxXfermode_DEFINED
     10 
     11 #include "Sk4px.h"
     12 #include "SkMSAN.h"
     13 #include "SkNx.h"
     14 #include "SkXfermodePriv.h"
     15 
     16 namespace {
     17 
     18 // Most xfermodes can be done most efficiently 4 pixels at a time in 8 or 16-bit fixed point.
     19 #define XFERMODE(Xfermode) \
     20     struct Xfermode { Sk4px operator()(const Sk4px&, const Sk4px&) const; }; \
     21     inline Sk4px Xfermode::operator()(const Sk4px& d, const Sk4px& s) const
     22 
     23 XFERMODE(Clear) { return Sk4px::DupPMColor(0); }
     24 XFERMODE(Src)   { return s; }
     25 XFERMODE(Dst)   { return d; }
     26 XFERMODE(SrcIn)   { return     s.approxMulDiv255(d.alphas()      ); }
     27 XFERMODE(SrcOut)  { return     s.approxMulDiv255(d.alphas().inv()); }
     28 XFERMODE(SrcOver) { return s + d.approxMulDiv255(s.alphas().inv()); }
     29 XFERMODE(DstIn)   { return SrcIn  ()(s,d); }
     30 XFERMODE(DstOut)  { return SrcOut ()(s,d); }
     31 XFERMODE(DstOver) { return SrcOver()(s,d); }
     32 
     33 // [ S * Da + (1 - Sa) * D]
     34 XFERMODE(SrcATop) { return (s * d.alphas() + d * s.alphas().inv()).div255(); }
     35 XFERMODE(DstATop) { return SrcATop()(s,d); }
     36 //[ S * (1 - Da) + (1 - Sa) * D ]
     37 XFERMODE(Xor) { return (s * d.alphas().inv() + d * s.alphas().inv()).div255(); }
     38 // [S + D ]
     39 XFERMODE(Plus) { return s.saturatedAdd(d); }
     40 // [S * D ]
     41 XFERMODE(Modulate) { return s.approxMulDiv255(d); }
     42 // [S + D - S * D]
     43 XFERMODE(Screen) {
     44     // Doing the math as S + (1-S)*D or S + (D - S*D) means the add and subtract can be done
     45     // in 8-bit space without overflow.  S + (1-S)*D is a touch faster because inv() is cheap.
     46     return s + d.approxMulDiv255(s.inv());
     47 }
     48 XFERMODE(Multiply) { return (s * d.alphas().inv() + d * s.alphas().inv() + s*d).div255(); }
     49 // [ Sa + Da - Sa*Da, Sc + Dc - 2*min(Sc*Da, Dc*Sa) ]  (And notice Sa*Da == min(Sa*Da, Da*Sa).)
     50 XFERMODE(Difference) {
     51     auto m = Sk4px::Wide::Min(s * d.alphas(), d * s.alphas()).div255();
     52     // There's no chance of underflow, and if we subtract m before adding s+d, no overflow.
     53     return (s - m) + (d - m.zeroAlphas());
     54 }
     55 // [ Sa + Da - Sa*Da, Sc + Dc - 2*Sc*Dc ]
     56 XFERMODE(Exclusion) {
     57     auto p = s.approxMulDiv255(d);
     58     // There's no chance of underflow, and if we subtract p before adding src+dst, no overflow.
     59     return (s - p) + (d - p.zeroAlphas());
     60 }
     61 
     62 // We take care to use exact math for these next few modes where alphas
     63 // and colors are calculated using significantly different math.  We need
     64 // to preserve premul invariants, and exact math makes this easier.
     65 //
     66 // TODO: Some of these implementations might be able to be sped up a bit
     67 // while maintaining exact math, but let's follow up with that.
     68 
     69 XFERMODE(HardLight) {
     70     auto sa = s.alphas(),
     71          da = d.alphas();
     72 
     73     auto srcover = s + (d * sa.inv()).div255();
     74 
     75     auto isLite = ((sa-s) < s).widenLoHi();
     76 
     77     auto lite = sa*da - ((da-d)*(sa-s) << 1),
     78          dark = s*d << 1,
     79          both = s*da.inv() + d*sa.inv();
     80 
     81     auto alphas = srcover;
     82     auto colors = (both + isLite.thenElse(lite, dark)).div255();
     83     return alphas.zeroColors() + colors.zeroAlphas();
     84 }
     85 XFERMODE(Overlay) { return HardLight()(s,d); }
     86 
     87 XFERMODE(Darken) {
     88     auto sa = s.alphas(),
     89          da = d.alphas();
     90 
     91     auto sda = (s*da).div255(),
     92          dsa = (d*sa).div255();
     93 
     94     auto srcover = s + (d * sa.inv()).div255(),
     95          dstover = d + (s * da.inv()).div255();
     96     auto alphas = srcover,
     97          colors = (sda < dsa).thenElse(srcover, dstover);
     98     return alphas.zeroColors() + colors.zeroAlphas();
     99 }
    100 XFERMODE(Lighten) {
    101     auto sa = s.alphas(),
    102          da = d.alphas();
    103 
    104     auto sda = (s*da).div255(),
    105          dsa = (d*sa).div255();
    106 
    107     auto srcover = s + (d * sa.inv()).div255(),
    108          dstover = d + (s * da.inv()).div255();
    109     auto alphas = srcover,
    110          colors = (dsa < sda).thenElse(srcover, dstover);
    111     return alphas.zeroColors() + colors.zeroAlphas();
    112 }
    113 #undef XFERMODE
    114 
    115 // Some xfermodes use math like divide or sqrt that's best done in floats 1 pixel at a time.
    116 #define XFERMODE(Xfermode) \
    117     struct Xfermode { Sk4f operator()(const Sk4f&, const Sk4f&) const; }; \
    118     inline Sk4f Xfermode::operator()(const Sk4f& d, const Sk4f& s) const
    119 
    120 static inline Sk4f a_rgb(const Sk4f& a, const Sk4f& rgb) {
    121     static_assert(SK_A32_SHIFT == 24, "");
    122     return a * Sk4f(0,0,0,1) + rgb * Sk4f(1,1,1,0);
    123 }
    124 static inline Sk4f alphas(const Sk4f& f) {
    125     return f[SK_A32_SHIFT/8];
    126 }
    127 
    128 XFERMODE(ColorDodge) {
    129     auto sa = alphas(s),
    130          da = alphas(d),
    131          isa = Sk4f(1)-sa,
    132          ida = Sk4f(1)-da;
    133 
    134     auto srcover = s + d*isa,
    135          dstover = d + s*ida,
    136          otherwise = sa * Sk4f::Min(da, (d*sa)*(sa-s).invert()) + s*ida + d*isa;
    137 
    138     // Order matters here, preferring d==0 over s==sa.
    139     auto colors = (d == Sk4f(0)).thenElse(dstover,
    140                   (s ==      sa).thenElse(srcover,
    141                                           otherwise));
    142     return a_rgb(srcover, colors);
    143 }
    144 XFERMODE(ColorBurn) {
    145     auto sa = alphas(s),
    146          da = alphas(d),
    147          isa = Sk4f(1)-sa,
    148          ida = Sk4f(1)-da;
    149 
    150     auto srcover = s + d*isa,
    151          dstover = d + s*ida,
    152          otherwise = sa*(da-Sk4f::Min(da, (da-d)*sa*s.invert())) + s*ida + d*isa;
    153 
    154     // Order matters here, preferring d==da over s==0.
    155     auto colors = (d ==      da).thenElse(dstover,
    156                   (s == Sk4f(0)).thenElse(srcover,
    157                                           otherwise));
    158     return a_rgb(srcover, colors);
    159 }
    160 XFERMODE(SoftLight) {
    161     auto sa = alphas(s),
    162          da = alphas(d),
    163          isa = Sk4f(1)-sa,
    164          ida = Sk4f(1)-da;
    165 
    166     // Some common terms.
    167     auto m  = (da > Sk4f(0)).thenElse(d / da, Sk4f(0)),
    168          s2 = Sk4f(2)*s,
    169          m4 = Sk4f(4)*m;
    170 
    171     // The logic forks three ways:
    172     //    1. dark src?
    173     //    2. light src, dark dst?
    174     //    3. light src, light dst?
    175     auto darkSrc = d*(sa + (s2 - sa)*(Sk4f(1) - m)),        // Used in case 1.
    176          darkDst = (m4*m4 + m4)*(m - Sk4f(1)) + Sk4f(7)*m,  // Used in case 2.
    177          liteDst = m.sqrt() - m,                            // Used in case 3.
    178          liteSrc = d*sa + da*(s2-sa)*(Sk4f(4)*d <= da).thenElse(darkDst, liteDst); // Case 2 or 3?
    179 
    180     auto alpha  = s + d*isa;
    181     auto colors = s*ida + d*isa + (s2 <= sa).thenElse(darkSrc, liteSrc);           // Case 1 or 2/3?
    182 
    183     return a_rgb(alpha, colors);
    184 }
    185 #undef XFERMODE
    186 
    187 // A reasonable fallback mode for doing AA is to simply apply the transfermode first,
    188 // then linearly interpolate the AA.
    189 template <typename Xfermode>
    190 static Sk4px xfer_aa(const Sk4px& d, const Sk4px& s, const Sk4px& aa) {
    191     Sk4px bw = Xfermode()(d, s);
    192     return (bw * aa + d * aa.inv()).div255();
    193 }
    194 
    195 // For some transfermodes we specialize AA, either for correctness or performance.
    196 #define XFERMODE_AA(Xfermode) \
    197     template <> Sk4px xfer_aa<Xfermode>(const Sk4px& d, const Sk4px& s, const Sk4px& aa)
    198 
    199 // Plus' clamp needs to happen after AA.  skia:3852
    200 XFERMODE_AA(Plus) {  // [ clamp( (1-AA)D + (AA)(S+D) ) == clamp(D + AA*S) ]
    201     return d.saturatedAdd(s.approxMulDiv255(aa));
    202 }
    203 
    204 #undef XFERMODE_AA
    205 
    206 // Src and Clear modes are safe to use with unitialized dst buffers,
    207 // even if the implementation branches based on bytes from dst (e.g. asserts in Debug mode).
    208 // For those modes, just lie to MSAN that dst is always intialized.
    209 template <typename Xfermode> static void mark_dst_initialized_if_safe(void*, void*) {}
    210 template <> void mark_dst_initialized_if_safe<Src>(void* dst, void* end) {
    211     sk_msan_mark_initialized(dst, end, "Src doesn't read dst.");
    212 }
    213 template <> void mark_dst_initialized_if_safe<Clear>(void* dst, void* end) {
    214     sk_msan_mark_initialized(dst, end, "Clear doesn't read dst.");
    215 }
    216 
    217 template <typename Xfermode>
    218 class Sk4pxXfermode : public SkXfermode {
    219 public:
    220     Sk4pxXfermode() {}
    221 
    222     void xfer32(SkPMColor dst[], const SkPMColor src[], int n, const SkAlpha aa[]) const override {
    223         mark_dst_initialized_if_safe<Xfermode>(dst, dst+n);
    224         if (nullptr == aa) {
    225             Sk4px::MapDstSrc(n, dst, src, Xfermode());
    226         } else {
    227             Sk4px::MapDstSrcAlpha(n, dst, src, aa, xfer_aa<Xfermode>);
    228         }
    229     }
    230 };
    231 
    232 template <typename Xfermode>
    233 class Sk4fXfermode : public SkXfermode {
    234 public:
    235     Sk4fXfermode() {}
    236 
    237     void xfer32(SkPMColor dst[], const SkPMColor src[], int n, const SkAlpha aa[]) const override {
    238         for (int i = 0; i < n; i++) {
    239             dst[i] = Xfer32_1(dst[i], src[i], aa ? aa+i : nullptr);
    240         }
    241     }
    242 
    243 private:
    244     static SkPMColor Xfer32_1(SkPMColor dst, const SkPMColor src, const SkAlpha* aa) {
    245         Sk4f d = Load(dst),
    246              s = Load(src),
    247              b = Xfermode()(d, s);
    248         if (aa) {
    249             Sk4f a = Sk4f(*aa) * Sk4f(1.0f/255);
    250             b = b*a + d*(Sk4f(1)-a);
    251         }
    252         return Round(b);
    253     }
    254 
    255     static Sk4f Load(SkPMColor c) {
    256         return SkNx_cast<float>(Sk4b::Load(&c)) * Sk4f(1.0f/255);
    257     }
    258 
    259     static SkPMColor Round(const Sk4f& f) {
    260         SkPMColor c;
    261         SkNx_cast<uint8_t>(f * Sk4f(255) + Sk4f(0.5f)).store(&c);
    262         return c;
    263     }
    264 };
    265 
    266 } // namespace
    267 
    268 namespace SK_OPTS_NS {
    269 
    270 static SkXfermode* create_xfermode(SkBlendMode mode) {
    271     switch (mode) {
    272 #define CASE(Xfermode) \
    273     case SkBlendMode::k##Xfermode: return new Sk4pxXfermode<Xfermode>()
    274         CASE(Clear);
    275         CASE(Src);
    276         CASE(Dst);
    277         CASE(SrcOver);
    278         CASE(DstOver);
    279         CASE(SrcIn);
    280         CASE(DstIn);
    281         CASE(SrcOut);
    282         CASE(DstOut);
    283         CASE(SrcATop);
    284         CASE(DstATop);
    285         CASE(Xor);
    286         CASE(Plus);
    287         CASE(Modulate);
    288         CASE(Screen);
    289         CASE(Multiply);
    290         CASE(Difference);
    291         CASE(Exclusion);
    292         CASE(HardLight);
    293         CASE(Overlay);
    294         CASE(Darken);
    295         CASE(Lighten);
    296     #undef CASE
    297 
    298 #define CASE(Xfermode) \
    299     case SkBlendMode::k##Xfermode: return new Sk4fXfermode<Xfermode>()
    300         CASE(ColorDodge);
    301         CASE(ColorBurn);
    302         CASE(SoftLight);
    303     #undef CASE
    304 
    305         default: break;
    306     }
    307     return nullptr;
    308 }
    309 
    310 } // namespace SK_OPTS_NS
    311 
    312 #endif//Sk4pxXfermode_DEFINED
    313