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 /include | |
| 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 'include')
| -rw-r--r-- | include/private/SkFixed.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/include/private/SkFixed.h b/include/private/SkFixed.h index adb0343bc7..05e1de49c9 100644 --- a/include/private/SkFixed.h +++ b/include/private/SkFixed.h @@ -30,6 +30,11 @@ typedef int32_t SkFixed; #define SK_FixedTanPIOver8 (0x6A0A) #define SK_FixedRoot2Over2 (0xB505) +// NOTE: SkFixedToFloat is exact. SkFloatToFixed seems to lack a rounding step. For all fixed-point +// values, this version is as accurate as possible for (fixed -> float -> fixed). Rounding reduces +// accuracy if the intermediate floats are in the range that only holds integers (adding 0.5f to an +// odd integer then snaps to nearest even). Using double for the rounding math gives maximum +// accuracy for (float -> fixed -> float), but that's usually overkill. #define SkFixedToFloat(x) ((x) * 1.52587890625e-5f) #define SkFloatToFixed(x) sk_float_saturate2int((x) * SK_Fixed1) |