diff options
Diffstat (limited to 'src/core')
| -rw-r--r-- | src/core/SkSRGB.h | 73 |
1 files changed, 15 insertions, 58 deletions
diff --git a/src/core/SkSRGB.h b/src/core/SkSRGB.h index 83ae5a4b27..9166ee9a2e 100644 --- a/src/core/SkSRGB.h +++ b/src/core/SkSRGB.h @@ -24,16 +24,8 @@ extern const float sk_linear_from_srgb[256]; extern const uint16_t sk_linear12_from_srgb[256]; extern const uint8_t sk_linear12_to_srgb[4096]; -template <typename V> -static inline V sk_clamp_0_255(const V& x) { - // The order of the arguments is important here. We want to make sure that NaN - // clamps to zero. Note that max(NaN, 0) = 0, while max(0, NaN) = NaN. - return V::Min(V::Max(x, 0.0f), 255.0f); -} - -// [0.0f, 1.0f] -> [0.0f, 255.xf], for small x. Correct after truncation. -template <typename V> -static inline V sk_linear_to_srgb_needs_trunc(const V& x) { +// [0.0f, 1.0f] -> [0, 255]. +static inline Sk4i sk_linear_to_srgb(const Sk4f& x) { // Approximation of the sRGB gamma curve (within 1 when scaled to 8-bit pixels). // // Constants tuned by brute force to minimize (in order of importance) after truncation: @@ -46,15 +38,19 @@ static inline V sk_linear_to_srgb_needs_trunc(const V& x) { auto lo = (13.0471f * 255.0f) * x; - auto hi = SkNx_fma(V{+0.412999f * 255.0f}, ftrt, - SkNx_fma(V{+0.687999f * 255.0f}, sqrt, - V{-0.0974983f * 255.0f})); - return (x < 0.0048f).thenElse(lo, hi); + auto hi = SkNx_fma(Sk4f{+0.412999f * 255.0f}, ftrt, + SkNx_fma(Sk4f{+0.687999f * 255.0f}, sqrt, + Sk4f{-0.0974983f * 255.0f})); + auto s = (x < 0.0048f).thenElse(lo, hi); + + // Now clamp and truncate. + // The order of the arguments is important here. We want to make sure that NaN + // clamps to zero. Note that max(NaN, 0) = 0, while max(0, NaN) = NaN. + return SkNx_cast<int>(Sk4f::Min(Sk4f::Max(s, 0.0f), 255.0f)); } // [0.0f, 1.0f] -> [0.0f, 1.0f]. Correct after rounding. -template <typename V> -static inline V sk_linear_to_srgb_needs_round(const V& x) { +static inline Sk4f sk_linear_to_srgb_needs_round(const Sk4f& x) { // Tuned to round trip each sRGB byte after rounding. auto rsqrt = x.rsqrt(), sqrt = rsqrt.invert(), @@ -62,49 +58,10 @@ static inline V sk_linear_to_srgb_needs_round(const V& x) { auto lo = 12.46f * x; - auto hi = V::Min(1.0f, SkNx_fma(V{+0.411192f}, ftrt, - SkNx_fma(V{+0.689206f}, sqrt, - V{-0.0988f}))); + auto hi = Sk4f::Min(1.0f, SkNx_fma(Sk4f{+0.411192f}, ftrt, + SkNx_fma(Sk4f{+0.689206f}, sqrt, + Sk4f{-0.0988f}))); return (x < 0.0043f).thenElse(lo, hi); } -template <int N> -static inline SkNx<N,int> sk_linear_to_srgb(const SkNx<N,float>& x) { - auto f = sk_linear_to_srgb_needs_trunc(x); - return SkNx_cast<int>(sk_clamp_0_255(f)); -} - - -// sRGB -> linear, using math instead of table lookups. -template <typename V> -static inline V sk_linear_from_srgb_math(const V& x) { - // Non-linear segment of sRGB curve approximated by - // l = 0.0025 + 0.6975x^2 + 0.3x^3 - const V k0 = 0.0025f, - k2 = 0.6975f, - k3 = 0.3000f; - auto hi = SkNx_fma(x*x, SkNx_fma(x, k3, k2), k0); - - // Linear segment of sRGB curve: the normal slope, extended a little further than normal. - auto lo = x * (1/12.92f); - - return (x < 0.055f).thenElse(lo, hi); -} - -// Same as above, starting from ints. -template <int N> -static inline SkNx<N,float> sk_linear_from_srgb_math(const SkNx<N,int>& s) { - auto x = SkNx_cast<float>(s); - - // Same math as above, but working with x in [0,255], so x^n needs scaling by u^n. - const float u = 1/255.0f; - - const SkNx<N,float> k0 = 0.0025f, - k2 = 0.6975f * u*u, - k3 = 0.3000f * u*u*u; - auto hi = SkNx_fma(x*x, SkNx_fma(x, k3, k2), k0); - auto lo = x * (u/12.92f); - return (x < (0.055f/u)).thenElse(lo, hi); -} - #endif//SkSRGB_DEFINED |