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LibGfx: Simplify and refactor Gamma.h

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Remove ACCURATE_GAMMA_ADJUSTMENT, since it makes the implementation
uglier, isn't guaranteed to make gamma adjustment accurate and is much
slower.  gamma_accurate_blend4 should either be always used or not
exist based on compilation flags, so there is no need to have it in
its own function. Finally, we should use AK/SIMD.h instead of defining
our own f32x4 type.
This commit is contained in:
Sahan Fernando 2020-12-08 10:53:25 +11:00 committed by Andreas Kling
parent d50934823a
commit 893adbb79c
Notes: sideshowbarker 2024-07-19 00:59:39 +09:00 
Author: https://github.com/ccapitalK
Commit: https://github.com/SerenityOS/serenity/commit/893adbb79c5
Pull-request: https://github.com/SerenityOS/serenity/pull/4354
Issue: https://github.com/SerenityOS/serenity/issues/69
1 changed files with 23 additions and 39 deletions
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62
Libraries/LibGfx/Gamma.h
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@ -30,6 +30,8 @@
#include <math.h>
#include <xmmintrin.h>
#include <AK/SIMD.h>
#define GAMMA 2.2
// Most computer graphics are stored in the sRGB color space, which stores something close to
@ -50,27 +52,28 @@
namespace Gfx {
using AK::SIMD::f32x4;
#ifndef NO_FPU
# ifdef __SSE__
// A vector of 4 floats, aligned for SSE instructions
typedef float v4sf __attribute__((vector_size(16)));
// Transform v4sf from gamma2.2 space to linear space
// Transform f32x4 from gamma2.2 space to linear space
// Assumes x is in range [0, 1]
// FIXME: Remove this hack once clang-11 is available as the default in Github Actions.
// This is apparently sometime mid-December. https://github.com/actions/virtual-environments/issues/2130
# if !defined(__clang__) || __clang_major__ >= 11
constexpr v4sf gamma_to_linear4(v4sf x)
constexpr f32x4 gamma_to_linear4(f32x4 x)
# else
inline v4sf gamma_to_linear4(v4sf x)
inline f32x4 gamma_to_linear4(f32x4 x)
# endif
{
return (0.8f + 0.2f * x) * x * x;
}
inline v4sf linear_to_gamma4(v4sf x)
// Transform f32x4 from linear space to gamma2.2 space
// Assumes x is in range [0, 1]
inline f32x4 linear_to_gamma4(f32x4 x)
{
// Source for approximation: https://mimosa-pudica.net/fast-gamma/
constexpr float a = 0.00279491f;
@ -81,59 +84,29 @@ inline v4sf linear_to_gamma4(v4sf x)
// Linearize v1 and v2, lerp them by mix factor, then convert back.
// The output is entirely v1 when mix = 0 and entirely v2 when mix = 1
inline v4sf gamma_accurate_lerp4(v4sf v1, v4sf v2, float mix)
inline f32x4 gamma_accurate_lerp4(f32x4 v1, f32x4 v2, float mix)
{
return linear_to_gamma4(gamma_to_linear4(v1) * (1 - mix) + gamma_to_linear4(v2) * mix);
}
// Convert a and b to linear space, blend them by mix factor, then convert back using sse1.
// The output is entirely a when mix = 0 and entirely b when mix = 1
inline Color gamma_accurate_blend4(Color a, Color b, float mix)
{
v4sf ac = {
(float)a.red(),
(float)a.green(),
(float)a.blue(),
0.f,
};
v4sf bc = {
(float)b.red(),
(float)b.green(),
(float)b.blue(),
0.f,
};
v4sf out = 255.f * gamma_accurate_lerp4(ac / 255.f, bc / 255.f, mix);
return Color(out[0], out[1], out[2]);
}
# endif
// Transform scalar from gamma2.2 space to linear space
// Assumes x is in range [0, 1]
constexpr float gamma_to_linear(float x)
{
# ifdef ACCURATE_GAMMA_ADJUSTMENT
// Slower, but more accurate
return pow(x, GAMMA);
# else
return (0.8 + 0.2 * x) * x * x;
# endif
}
// Transform scalar from linear space to gamma2.2 space
// Assumes x is in range [0, 1]
inline float linear_to_gamma(float x)
{
# ifdef ACCURATE_GAMMA_ADJUSTMENT
// Slower, but more accurate
return pow(x, 1. / GAMMA);
# else
// Source for approximation: https://mimosa-pudica.net/fast-gamma/
constexpr float a = 0.00279491;
constexpr float b = 1.15907984;
float c = (b / sqrt(1 + a)) - 1;
return ((b / __builtin_sqrt(x + a)) - c) * x;
# endif
}
// Linearize v1 and v2, lerp them by mix factor, then convert back.
@ -148,7 +121,18 @@ inline float gamma_accurate_lerp(float v1, float v2, float mix)
inline Color gamma_accurate_blend(Color a, Color b, float mix)
{
# ifdef __SSE__
return gamma_accurate_blend4(a, b, mix);
f32x4 ac = {
(float)a.red(),
(float)a.green(),
(float)a.blue(),
};
f32x4 bc = {
(float)b.red(),
(float)b.green(),
(float)b.blue(),
};
f32x4 out = 255.f * gamma_accurate_lerp4(ac * (1.f / 255.f), bc * (1.f / 255.f), mix);
return Color(out[0], out[1], out[2]);
# else
return {
static_cast<u8>(255. * gamma_accurate_lerp(a.red() / 255., b.red() / 255., mix)),