| /* |
| * Copyright 2016 Google Inc. |
| * |
| * Use of this source code is governed by a BSD-style license that can be |
| * found in the LICENSE file. |
| */ |
| |
| #ifndef SkSRGB_DEFINED |
| #define SkSRGB_DEFINED |
| |
| #include "SkNx.h" |
| |
| /** Components for building our canonical sRGB -> linear and linear -> sRGB transformations. |
| * |
| * Current best practices: |
| * - for sRGB -> linear, lookup R,G,B in sk_linear_from_srgb; |
| * - for linear -> sRGB, call sk_linear_to_srgb() for R,G,B; |
| * - the alpha channel is linear in both formats, needing at most *(1/255.0f) or *255.0f. |
| * |
| * sk_linear_to_srgb() will run a little faster than usual when compiled with SSE4.1+. |
| */ |
| |
| extern const float sk_linear_from_srgb[256]; |
| |
| static inline Sk4f sk_clamp_0_255(const Sk4f& 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 Sk4f::Min(Sk4f::Max(x, 0.0f), 255.0f); |
| } |
| |
| static inline Sk4i sk_linear_to_srgb(const Sk4f& x) { |
| // Approximation of the sRGB gamma curve (within 1 when scaled to 8-bit pixels). |
| // |
| // Tuned by brute force to minimize the number of bytes that fail to round trip, |
| // here 0 (of 256), and then to minimize the number of points halfway between bytes |
| // (in linear space) that fail to hit the right byte, here 131 (of 255), and to |
| // minimize the number of monotonicity regressions over the range [0,1], here 0. |
| |
| auto rsqrt = x.rsqrt(), |
| sqrt = rsqrt.invert(), |
| ftrt = rsqrt.rsqrt(); |
| |
| auto lo = (13.0471f * 255.0f) * x; |
| |
| auto hi = (-0.0974983f * 255.0f) |
| + (+0.687999f * 255.0f) * sqrt |
| + (+0.412999f * 255.0f) * ftrt; |
| |
| return SkNx_cast<int>(sk_clamp_0_255((x < 0.0048f).thenElse(lo, hi))); |
| } |
| |
| #endif//SkSRGB_DEFINED |