start experimenting with 64bit frame-buffers

src/core/SkXfermodeU64.cpp

Index: src/core/SkXfermodeU64.cpp
diff --git a/src/core/SkXfermodeU64.cpp b/src/core/SkXfermodeU64.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..6435e6a2e2b0aa170e8a6fb5502283a9e13f8fa1
--- /dev/null
+++ b/src/core/SkXfermodeU64.cpp
@@ -0,0 +1,181 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkHalf.h"
+#include "SkPM4fPriv.h"
+#include "SkUtils.h"
+#include "SkXfermode.h"
+
+static void sk_memset64(uint64_t dst[], uint64_t value, int count) {
+    for (int i = 0; i < count; ++i) {
+        dst[i] = value;
+    }
+}
+
+struct U64ProcPair {
+    SkXfermode::U64Proc1 fP1;
+    SkXfermode::U64ProcN fPN;
+};
+
+enum DstType {
+    kU16_Dst,
+    kF16_Dst,
+};
+
+static Sk4f lerp_by_coverage(const Sk4f& src, const Sk4f& dst, uint8_t srcCoverage) {
+    return dst + (src - dst) * Sk4f(srcCoverage * (1/255.0f));
+}
+
+template <DstType D> Sk4f unit_to_dst_bias(const Sk4f& x4) {
+    return (D == kU16_Dst) ? x4 * Sk4f(65535) : x4;
+}
+
+// returns value already biased by 65535
+static Sk4f load_from_u16(uint64_t value) {
+    return SkNx_cast<float>(Sk4h::Load(&value));
+}
+
+// takes floats already biased by 65535
+static uint64_t store_to_u16(const Sk4f& x4) {
+    uint64_t value;
+    SkNx_cast<uint16_t>(x4 + Sk4f(0.5f)).store(&value);
+    return value;
+}
+
+static Sk4f load_from_f16(uint64_t value) {
+    const uint16_t* u16 = reinterpret_cast<const uint16_t*>(&value);
+    float f4[4];
+    for (int i = 0; i < 4; ++i) {
+        f4[i] = SkHalfToFloat(u16[i]);
+    }
+    return Sk4f::Load(f4);
+}
+
+static uint64_t store_to_f16(const Sk4f& x4) {
+    uint64_t value;
+    uint16_t* u16 = reinterpret_cast<uint16_t*>(&value);
+
+    float f4[4];
+    x4.store(f4);
+    for (int i = 0; i < 4; ++i) {
+        u16[i] = SkFloatToHalf(f4[i]);
+    }
+    return value;
+}
+
+// Returns dst in its "natural" bias (either unit-float or 16bit int)
+//
+template <DstType D> Sk4f load_from_dst(uint64_t dst) {
+    return (D == kU16_Dst) ? load_from_u16(dst) : load_from_f16(dst);
+}
+
+// Assumes x4 is already in the "natural" bias (either unit-float or 16bit int)
+template <DstType D> uint64_t store_to_dst(const Sk4f& x4) {
+    return (D == kU16_Dst) ? store_to_u16(x4) : store_to_f16(x4);
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+template <DstType D> void src_1(const SkXfermode::U64State& state, uint64_t dst[],
+                                const SkPM4f& src, int count, const SkAlpha aa[]) {
+    const Sk4f s4 = unit_to_dst_bias<D>(Sk4f::Load(src.fVec));
+    if (aa) {
+        for (int i = 0; i < count; ++i) {
+            const Sk4f d4 = load_from_dst<D>(dst[i]);
+            dst[i] = store_to_dst<D>(lerp_by_coverage(s4, d4, aa[i]));
+        }
+    } else {
+        sk_memset64(dst, store_to_dst<D>(s4), count);
+    }
+}
+
+template <DstType D> void src_n(const SkXfermode::U64State& state, uint64_t dst[],
+                                const SkPM4f src[], int count, const SkAlpha aa[]) {
+    if (aa) {
+        for (int i = 0; i < count; ++i) {
+            const Sk4f s4 = unit_to_dst_bias<D>(Sk4f::Load(src[i].fVec));
+            const Sk4f d4 = load_from_dst<D>(dst[i]);
+            dst[i] = store_to_dst<D>(lerp_by_coverage(s4, d4, aa[i]));
+        }
+    } else {
+        for (int i = 0; i < count; ++i) {
+            const Sk4f s4 = unit_to_dst_bias<D>(Sk4f::Load(src[i].fVec));
+            dst[i] = store_to_dst<D>(s4);
+        }
+    }
+}
+
+const U64ProcPair gU64Procs_Src[] = {
+    { src_1<kU16_Dst>, src_n<kU16_Dst>  },   // U16     alpha
+    { src_1<kU16_Dst>, src_n<kU16_Dst>  },   // U16     opaque
+    { src_1<kF16_Dst>, src_n<kF16_Dst>  },   // F16     alpha
+    { src_1<kF16_Dst>, src_n<kF16_Dst>  },   // F16     opaque
+};
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+template <DstType D> void srcover_1(const SkXfermode::U64State& state, uint64_t dst[],
+                                    const SkPM4f& src, int count, const SkAlpha aa[]) {
+    const Sk4f s4 = Sk4f::Load(src.fVec);
+    const Sk4f dst_scale = Sk4f(1 - get_alpha(s4));
+    const Sk4f s4bias = unit_to_dst_bias<D>(s4);
+    for (int i = 0; i < count; ++i) {
+        const Sk4f d4bias = load_from_dst<D>(dst[i]);
+        const Sk4f r4bias = s4bias + d4bias * dst_scale;
+        if (aa) {
+            dst[i] = store_to_dst<D>(lerp_by_coverage(r4bias, d4bias, aa[i]));
+        } else {
+            dst[i] = store_to_dst<D>(r4bias);
+        }
+    }
+}
+
+template <DstType D> void srcover_n(const SkXfermode::U64State& state, uint64_t dst[],
+                                    const SkPM4f src[], int count, const SkAlpha aa[]) {
+    for (int i = 0; i < count; ++i) {
+        const Sk4f s4 = Sk4f::Load(src[i].fVec);
+        const Sk4f dst_scale = Sk4f(1 - get_alpha(s4));
+        const Sk4f s4bias = unit_to_dst_bias<D>(s4);
+        const Sk4f d4bias = load_from_dst<D>(dst[i]);
+        const Sk4f r4bias = s4bias + d4bias * dst_scale;
+        if (aa) {
+            dst[i] = store_to_dst<D>(lerp_by_coverage(r4bias, d4bias, aa[i]));
+        } else {
+            dst[i] = store_to_dst<D>(r4bias);
+        }
+    }
+}
+
+const U64ProcPair gU64Procs_SrcOver[] = {
+    { srcover_1<kU16_Dst>,  srcover_n<kU16_Dst> },   // U16     alpha
+    { src_1<kU16_Dst>,      src_n<kU16_Dst>     },   // U16     opaque
+    { srcover_1<kF16_Dst>,  srcover_n<kF16_Dst> },   // F16     alpha
+    { src_1<kF16_Dst>,      src_n<kF16_Dst>     },   // F16     opaque
+};
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+static U64ProcPair find_procs(SkXfermode::Mode mode, uint32_t flags) {
+    SkASSERT(0 == (flags & ~3));
+    flags &= 3;
+
+    switch (mode) {
+        case SkXfermode::kSrc_Mode:     return gU64Procs_Src[flags];
+        case SkXfermode::kSrcOver_Mode: return gU64Procs_SrcOver[flags];
+        default:
+            break;
+    }
+    return { nullptr, nullptr };
+}
+
+SkXfermode::U64Proc1 SkXfermode::GetU64Proc1(Mode mode, uint32_t flags) {
+    return find_procs(mode, flags).fP1;
+}
+
+SkXfermode::U64ProcN SkXfermode::GetU64ProcN(Mode mode, uint32_t flags) {
+    return find_procs(mode, flags).fPN;
+}