Port SkXfermode opts to SkOpts.h

Renames Sk4pxXfermode.h to SkXfermode_opts.h,
and refactors it a tiny bit internally.

This moves xfermode optimization from being "compile-time everywhere but NEON"
to simply "runtime everywhere".  I don't anticipate any effect on perf or
correctness.

BUG=skia:4117

Review URL: https://codereview.chromium.org/1264543006

1 files changed, 321 insertions, 0 deletions

diff --git a/src/opts/SkXfermode_opts.h b/src/opts/SkXfermode_opts.h
new file mode 100644
index 0000000000..6bc76fe559
--- /dev/null
+++ b/src/opts/SkXfermode_opts.h
@@ -0,0 +1,321 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef Sk4pxXfermode_DEFINED
+#define Sk4pxXfermode_DEFINED
+
+#include "Sk4px.h"
+#include "SkPMFloat.h"
+#include "SkXfermode_proccoeff.h"
+
+// This file is possibly included into multiple .cpp files.
+// Each gets its own independent instantiation by wrapping in an anonymous namespace.
+namespace {
+
+// Most xfermodes can be done most efficiently 4 pixels at a time in 8 or 16-bit fixed point.
+#define XFERMODE(Name) static Sk4px SK_VECTORCALL Name(Sk4px s, Sk4px d)
+
+XFERMODE(Clear) { return Sk4px::DupPMColor(0); }
+XFERMODE(Src)   { return s; }
+XFERMODE(Dst)   { return d; }
+XFERMODE(SrcIn)   { return     s.approxMulDiv255(d.alphas()      ); }
+XFERMODE(SrcOut)  { return     s.approxMulDiv255(d.alphas().inv()); }
+XFERMODE(SrcOver) { return s + d.approxMulDiv255(s.alphas().inv()); }
+XFERMODE(DstIn)   { return SrcIn  (d,s); }
+XFERMODE(DstOut)  { return SrcOut (d,s); }
+XFERMODE(DstOver) { return SrcOver(d,s); }
+
+// [ S * Da + (1 - Sa) * D]
+XFERMODE(SrcATop) { return (s * d.alphas() + d * s.alphas().inv()).div255(); }
+XFERMODE(DstATop) { return SrcATop(d,s); }
+//[ S * (1 - Da) + (1 - Sa) * D ]
+XFERMODE(Xor) { return (s * d.alphas().inv() + d * s.alphas().inv()).div255(); }
+// [S + D ]
+XFERMODE(Plus) { return s.saturatedAdd(d); }
+// [S * D ]
+XFERMODE(Modulate) { return s.approxMulDiv255(d); }
+// [S + D - S * D]
+XFERMODE(Screen) {
+    // Doing the math as S + (1-S)*D or S + (D - S*D) means the add and subtract can be done
+    // in 8-bit space without overflow.  S + (1-S)*D is a touch faster because inv() is cheap.
+    return s + d.approxMulDiv255(s.inv());
+}
+XFERMODE(Multiply) { return (s * d.alphas().inv() + d * s.alphas().inv() + s*d).div255(); }
+// [ Sa + Da - Sa*Da, Sc + Dc - 2*min(Sc*Da, Dc*Sa) ]  (And notice Sa*Da == min(Sa*Da, Da*Sa).)
+XFERMODE(Difference) {
+    auto m = Sk4px::Wide::Min(s * d.alphas(), d * s.alphas()).div255();
+    // There's no chance of underflow, and if we subtract m before adding s+d, no overflow.
+    return (s - m) + (d - m.zeroAlphas());
+}
+// [ Sa + Da - Sa*Da, Sc + Dc - 2*Sc*Dc ]
+XFERMODE(Exclusion) {
+    auto p = s.approxMulDiv255(d);
+    // There's no chance of underflow, and if we subtract p before adding src+dst, no overflow.
+    return (s - p) + (d - p.zeroAlphas());
+}
+
+// We take care to use exact math for these next few modes where alphas
+// and colors are calculated using significantly different math.  We need
+// to preserve premul invariants, and exact math makes this easier.
+//
+// TODO: Some of these implementations might be able to be sped up a bit
+// while maintaining exact math, but let's follow up with that.
+
+XFERMODE(HardLight) {
+    auto sa = s.alphas(),
+         da = d.alphas();
+
+    auto srcover = s + (d * sa.inv()).div255();
+
+    auto isLite = ((sa-s) < s).widenLoHi();
+
+    auto lite = sa*da - ((da-d)*(sa-s) << 1),
+         dark = s*d << 1,
+         both = s*da.inv() + d*sa.inv();
+
+    auto alphas = srcover;
+    auto colors = (both + isLite.thenElse(lite, dark)).div255();
+    return alphas.zeroColors() + colors.zeroAlphas();
+}
+XFERMODE(Overlay) { return HardLight(d,s); }
+
+XFERMODE(Darken) {
+    auto sa = s.alphas(),
+         da = d.alphas();
+
+    auto sda = (s*da).div255(),
+         dsa = (d*sa).div255();
+
+    auto srcover = s + (d * sa.inv()).div255(),
+         dstover = d + (s * da.inv()).div255();
+    auto alphas = srcover,
+         colors = (sda < dsa).thenElse(srcover, dstover);
+    return alphas.zeroColors() + colors.zeroAlphas();
+}
+XFERMODE(Lighten) {
+    auto sa = s.alphas(),
+         da = d.alphas();
+
+    auto sda = (s*da).div255(),
+         dsa = (d*sa).div255();
+
+    auto srcover = s + (d * sa.inv()).div255(),
+         dstover = d + (s * da.inv()).div255();
+    auto alphas = srcover,
+         colors = (dsa < sda).thenElse(srcover, dstover);
+    return alphas.zeroColors() + colors.zeroAlphas();
+}
+#undef XFERMODE
+
+// Some xfermodes use math like divide or sqrt that's best done in floats 1 pixel at a time.
+#define XFERMODE(Name) static SkPMFloat SK_VECTORCALL Name(SkPMFloat s, SkPMFloat d)
+
+XFERMODE(ColorDodge) {
+    auto sa = s.alphas(),
+         da = d.alphas(),
+         isa = Sk4f(1)-sa,
+         ida = Sk4f(1)-da;
+
+    auto srcover = s + d*isa,
+         dstover = d + s*ida,
+         otherwise = sa * Sk4f::Min(da, (d*sa)*(sa-s).approxInvert()) + s*ida + d*isa;
+
+    // Order matters here, preferring d==0 over s==sa.
+    auto colors = (d == Sk4f(0)).thenElse(dstover,
+                  (s ==      sa).thenElse(srcover,
+                                          otherwise));
+    return srcover * SkPMFloat(1,0,0,0) + colors * SkPMFloat(0,1,1,1);
+}
+XFERMODE(ColorBurn) {
+    auto sa = s.alphas(),
+         da = d.alphas(),
+         isa = Sk4f(1)-sa,
+         ida = Sk4f(1)-da;
+
+    auto srcover = s + d*isa,
+         dstover = d + s*ida,
+         otherwise = sa*(da-Sk4f::Min(da, (da-d)*sa*s.approxInvert())) + s*ida + d*isa;
+
+    // Order matters here, preferring d==da over s==0.
+    auto colors = (d ==      da).thenElse(dstover,
+                  (s == Sk4f(0)).thenElse(srcover,
+                                          otherwise));
+    return srcover * SkPMFloat(1,0,0,0) + colors * SkPMFloat(0,1,1,1);
+}
+XFERMODE(SoftLight) {
+    auto sa = s.alphas(),
+         da = d.alphas(),
+         isa = Sk4f(1)-sa,
+         ida = Sk4f(1)-da;
+
+    // Some common terms.
+    auto m  = (da > Sk4f(0)).thenElse(d / da, Sk4f(0)),
+         s2 = Sk4f(2)*s,
+         m4 = Sk4f(4)*m;
+
+    // The logic forks three ways:
+    //    1. dark src?
+    //    2. light src, dark dst?
+    //    3. light src, light dst?
+    auto darkSrc = d*(sa + (s2 - sa)*(Sk4f(1) - m)),        // Used in case 1.
+         darkDst = (m4*m4 + m4)*(m - Sk4f(1)) + Sk4f(7)*m,  // Used in case 2.
+         liteDst = m.sqrt() - m,                            // Used in case 3.
+         liteSrc = d*sa + da*(s2-sa)*(Sk4f(4)*d <= da).thenElse(darkDst, liteDst); // Case 2 or 3?
+
+    auto alpha  = s + d*isa;
+    auto colors = s*ida + d*isa + (s2 <= sa).thenElse(darkSrc, liteSrc);           // Case 1 or 2/3?
+
+    return alpha * SkPMFloat(1,0,0,0) + colors * SkPMFloat(0,1,1,1);
+}
+#undef XFERMODE
+
+// A reasonable fallback mode for doing AA is to simply apply the transfermode first,
+// then linearly interpolate the AA.
+template <Sk4px (SK_VECTORCALL *Mode)(Sk4px, Sk4px)>
+static Sk4px SK_VECTORCALL xfer_aa(Sk4px s, Sk4px d, Sk4px aa) {
+    Sk4px bw = Mode(s, d);
+    return (bw * aa + d * aa.inv()).div255();
+}
+
+// For some transfermodes we specialize AA, either for correctness or performance.
+#define XFERMODE_AA(Name) \
+    template <> Sk4px SK_VECTORCALL xfer_aa<Name>(Sk4px s, Sk4px d, Sk4px aa)
+
+// Plus' clamp needs to happen after AA.  skia:3852
+XFERMODE_AA(Plus) {  // [ clamp( (1-AA)D + (AA)(S+D) ) == clamp(D + AA*S) ]
+    return d.saturatedAdd(s.approxMulDiv255(aa));
+}
+
+#undef XFERMODE_AA
+
+class Sk4pxXfermode : public SkProcCoeffXfermode {
+public:
+    typedef Sk4px (SK_VECTORCALL *Proc4)(Sk4px, Sk4px);
+    typedef Sk4px (SK_VECTORCALL *AAProc4)(Sk4px, Sk4px, Sk4px);
+
+    Sk4pxXfermode(const ProcCoeff& rec, SkXfermode::Mode mode, Proc4 proc4, AAProc4 aaproc4)
+        : INHERITED(rec, mode)
+        , fProc4(proc4)
+        , fAAProc4(aaproc4) {}
+
+    void xfer32(SkPMColor dst[], const SkPMColor src[], int n, const SkAlpha aa[]) const override {
+        if (NULL == aa) {
+            Sk4px::MapDstSrc(n, dst, src, [&](const Sk4px& dst4, const Sk4px& src4) {
+                return fProc4(src4, dst4);
+            });
+        } else {
+            Sk4px::MapDstSrcAlpha(n, dst, src, aa,
+                    [&](const Sk4px& dst4, const Sk4px& src4, const Sk4px& alpha) {
+                return fAAProc4(src4, dst4, alpha);
+            });
+        }
+    }
+
+    void xfer16(uint16_t dst[], const SkPMColor src[], int n, const SkAlpha aa[]) const override {
+        if (NULL == aa) {
+            Sk4px::MapDstSrc(n, dst, src, [&](const Sk4px& dst4, const Sk4px& src4) {
+                return fProc4(src4, dst4);
+            });
+        } else {
+            Sk4px::MapDstSrcAlpha(n, dst, src, aa,
+                    [&](const Sk4px& dst4, const Sk4px& src4, const Sk4px& alpha) {
+                return fAAProc4(src4, dst4, alpha);
+            });
+        }
+    }
+
+private:
+    Proc4 fProc4;
+    AAProc4 fAAProc4;
+    typedef SkProcCoeffXfermode INHERITED;
+};
+
+class SkPMFloatXfermode : public SkProcCoeffXfermode {
+public:
+    typedef SkPMFloat (SK_VECTORCALL *ProcF)(SkPMFloat, SkPMFloat);
+    SkPMFloatXfermode(const ProcCoeff& rec, SkXfermode::Mode mode, ProcF procf)
+        : INHERITED(rec, mode)
+        , fProcF(procf) {}
+
+    void xfer32(SkPMColor dst[], const SkPMColor src[], int n, const SkAlpha aa[]) const override {
+        for (int i = 0; i < n; i++) {
+            dst[i] = aa ? this->xfer32(dst[i], src[i], aa[i])
+                        : this->xfer32(dst[i], src[i]);
+        }
+    }
+
+    void xfer16(uint16_t dst[], const SkPMColor src[], int n, const SkAlpha aa[]) const override {
+        for (int i = 0; i < n; i++) {
+            SkPMColor dst32 = SkPixel16ToPixel32(dst[i]);
+            dst32 = aa ? this->xfer32(dst32, src[i], aa[i])
+                       : this->xfer32(dst32, src[i]);
+            dst[i] = SkPixel32ToPixel16(dst32);
+        }
+    }
+
+private:
+    inline SkPMColor xfer32(SkPMColor dst, SkPMColor src) const {
+        return fProcF(SkPMFloat(src), SkPMFloat(dst)).round();
+    }
+
+    inline SkPMColor xfer32(SkPMColor dst, SkPMColor src, SkAlpha aa) const {
+        SkPMFloat s(src),
+                  d(dst),
+                  b(fProcF(s,d));
+        // We do aa in full float precision before going back down to bytes, because we can!
+        SkPMFloat a = Sk4f(aa) * Sk4f(1.0f/255);
+        b = b*a + d*(Sk4f(1)-a);
+        return b.round();
+    }
+
+    ProcF fProcF;
+    typedef SkProcCoeffXfermode INHERITED;
+};
+
+static SkXfermode* SkCreate4pxXfermode(const ProcCoeff& rec, SkXfermode::Mode mode) {
+    switch (mode) {
+    #define CASE(Mode) case SkXfermode::k##Mode##_Mode: \
+        return SkNEW_ARGS(Sk4pxXfermode, (rec, mode, &Mode, &xfer_aa<Mode>))
+        CASE(Clear);
+        CASE(Src);
+        CASE(Dst);
+        CASE(SrcOver);
+        CASE(DstOver);
+        CASE(SrcIn);
+        CASE(DstIn);
+        CASE(SrcOut);
+        CASE(DstOut);
+        CASE(SrcATop);
+        CASE(DstATop);
+        CASE(Xor);
+        CASE(Plus);
+        CASE(Modulate);
+        CASE(Screen);
+        CASE(Multiply);
+        CASE(Difference);
+        CASE(Exclusion);
+        CASE(HardLight);
+        CASE(Overlay);
+        CASE(Darken);
+        CASE(Lighten);
+    #undef CASE
+
+    #define CASE(Mode) case SkXfermode::k##Mode##_Mode: \
+        return SkNEW_ARGS(SkPMFloatXfermode, (rec, mode, &Mode))
+        CASE(ColorDodge);
+        CASE(ColorBurn);
+        CASE(SoftLight);
+    #undef CASE
+
+        default: break;
+    }
+    return nullptr;
+}
+
+} // namespace
+
+#endif//Sk4pxXfermode_DEFINED