diff options
| author |  Brian Osman <brianosman@google.com> | 2017-12-18 10:14:12 -0500 |
|---|---|---|
| committer |  Skia Commit-Bot <skia-commit-bot@chromium.org> | 2017-12-18 19:49:12 +0000 |
| commit | ff5000830544f23a2af7a861068b1a8deebef7ba (patch) | |
| tree | 9963fed8e741cd16ad0dc1b61eb9bde85e360d0a /src | |
| parent | f1f1162273b382db99f8609e5bbfff24f5594821 (diff) | |
Increase accuracy of float -> fixed in ICC code
Add a comment to SkFixed explaining the accuracy issues of the macros.
Re-land of: https://skia-review.googlesource.com/85742
Bug: skia:
Change-Id: I09cef45bdb858608a6afe6c30424d8046cac50ec
Reviewed-on: https://skia-review.googlesource.com/86540
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Diffstat (limited to 'src')
| -rw-r--r-- | src/core/SkICC.cpp | 32 |
1 files changed, 22 insertions, 10 deletions
diff --git a/src/core/SkICC.cpp b/src/core/SkICC.cpp index 128bce368d..5ed4e70560 100644 --- a/src/core/SkICC.cpp +++ b/src/core/SkICC.cpp @@ -281,25 +281,37 @@ static constexpr uint32_t kICCTagTable[3 * kICCNumEntries] { SkEndian_SwapBE32(kTAG_cprt_Bytes), }; +// This is like SkFloatToFixed, but rounds to nearest, preserving as much accuracy as possible +// when going float -> fixed -> float (it has the same accuracy when going fixed -> float -> fixed). +// The use of double is necessary to accomodate the full potential 32-bit mantissa of the 16.16 +// SkFixed value, and so avoiding rounding problems with float. Also, see the comment in SkFixed.h. +static SkFixed float_round_to_fixed(float x) { +#if defined(SK_SUPPORT_LEGACY_ICC_PRECISON) + return SkFloatToFixed(x); +#else + return sk_float_saturate2int((float)floor((double)x * SK_Fixed1 + 0.5)); +#endif +} + static void write_xyz_tag(uint32_t* ptr, const SkMatrix44& toXYZ, int col) { ptr[0] = SkEndian_SwapBE32(kXYZ_PCSSpace); ptr[1] = 0; - ptr[2] = SkEndian_SwapBE32(SkFloatToFixed(toXYZ.getFloat(0, col))); - ptr[3] = SkEndian_SwapBE32(SkFloatToFixed(toXYZ.getFloat(1, col))); - ptr[4] = SkEndian_SwapBE32(SkFloatToFixed(toXYZ.getFloat(2, col))); + ptr[2] = SkEndian_SwapBE32(float_round_to_fixed(toXYZ.getFloat(0, col))); + ptr[3] = SkEndian_SwapBE32(float_round_to_fixed(toXYZ.getFloat(1, col))); + ptr[4] = SkEndian_SwapBE32(float_round_to_fixed(toXYZ.getFloat(2, col))); } static void write_trc_tag(uint32_t* ptr, const SkColorSpaceTransferFn& fn) { ptr[0] = SkEndian_SwapBE32(kTAG_ParaCurveType); ptr[1] = 0; ptr[2] = (uint32_t) (SkEndian_SwapBE16(kGABCDEF_ParaCurveType)); - ptr[3] = SkEndian_SwapBE32(SkFloatToFixed(fn.fG)); - ptr[4] = SkEndian_SwapBE32(SkFloatToFixed(fn.fA)); - ptr[5] = SkEndian_SwapBE32(SkFloatToFixed(fn.fB)); - ptr[6] = SkEndian_SwapBE32(SkFloatToFixed(fn.fC)); - ptr[7] = SkEndian_SwapBE32(SkFloatToFixed(fn.fD)); - ptr[8] = SkEndian_SwapBE32(SkFloatToFixed(fn.fE)); - ptr[9] = SkEndian_SwapBE32(SkFloatToFixed(fn.fF)); + ptr[3] = SkEndian_SwapBE32(float_round_to_fixed(fn.fG)); + ptr[4] = SkEndian_SwapBE32(float_round_to_fixed(fn.fA)); + ptr[5] = SkEndian_SwapBE32(float_round_to_fixed(fn.fB)); + ptr[6] = SkEndian_SwapBE32(float_round_to_fixed(fn.fC)); + ptr[7] = SkEndian_SwapBE32(float_round_to_fixed(fn.fD)); + ptr[8] = SkEndian_SwapBE32(float_round_to_fixed(fn.fE)); + ptr[9] = SkEndian_SwapBE32(float_round_to_fixed(fn.fF)); } static bool is_3x3(const SkMatrix44& toXYZD50) { |