1/* 2 * Copyright 2017 Google Inc. 3 * 4 * Use of this source code is governed by a BSD-style license that can be 5 * found in the LICENSE file. 6 */ 7 8#include "gm.h" 9#include "sk_tool_utils.h" 10 11// Hue, Saturation, Color, and Luminosity blend modes are oddballs. 12// They nominally convert their inputs to unpremul, then to HSL, then 13// mix-and-match H,S,and L from Src and Dst, then convert back, then premul. 14// 15// In practice that's slow, so instead we pick the color with the correct 16// Hue, and then (approximately) apply the other's Saturation and/or Luminosity. 17// This isn't just an optimization... it's how the modes are specified. 18// 19// Each mode's name describes the Src H,S,L components to keep, taking the 20// others from Dst, where Color == Hue + Saturation. Color and Luminosity 21// are each other's complements; Hue and Saturation have no complement. 22// 23// All these modes were originally designed to operate on gamma-encoded values, 24// and that's what everyone's used to seeing. It's unclear wehther they make 25// any sense in a gamma-correct world. They certainly won't look at all similar. 26// 27// We have had many inconsistent implementations of these modes. 28// This GM tries to demonstrate unambigously how they should work. 29// 30// To go along with our inconsistent implementations, there are two slightly 31// inconsistent specifications of how to perform these blends, 32// web: https://www.w3.org/TR/compositing-1/#blendingnonseparable 33// KHR: https://www.khronos.org/registry/OpenGL/extensions/KHR/KHR_blend_equation_advanced.txt 34// It looks like these are meant to be identical, but they disagree on at least ClipColor(). 35// 36// I think the KHR version is just wrong... it produces values >1. So we use the web version. 37 38static float min(float r, float g, float b) { return SkTMin(r, SkTMin(g, b)); } 39static float max(float r, float g, float b) { return SkTMax(r, SkTMax(g, b)); } 40 41static float sat(float r, float g, float b) { return max(r,g,b) - min(r,g,b); } 42static float lum(float r, float g, float b) { return r*0.30f + g*0.59f + b*0.11f; } 43 44// The two SetSat() routines in the specs look different, but they're logically equivalent. 45// Both map the minimum channel to 0, maximum to s, and scale the middle proportionately. 46// The KHR version has done a better job at simplifying its math, so we use it here. 47static void set_sat(float* r, float* g, float* b, float s) { 48 float mn = min(*r,*g,*b), 49 mx = max(*r,*g,*b); 50 auto channel = [=](float c) { 51 return mx == mn ? 0 52 : (c - mn) * s / (mx - mn); 53 }; 54 *r = channel(*r); 55 *g = channel(*g); 56 *b = channel(*b); 57} 58static void clip_color(float* r, float* g, float* b) { 59 float l = lum(*r,*g,*b), 60 mn = min(*r,*g,*b), 61 mx = max(*r,*g,*b); 62 auto clip = [=](float c) { 63 if (mn < 0) { c = l + (c - l) * ( l) / (l - mn); } 64 if (mx > 1) { c = l + (c - l) * (1 - l) / (mx - l); } 65 SkASSERT(-0.0001f < c); // This may end up very slightly negative... 66 SkASSERT( c <= 1); 67 return c; 68 }; 69 *r = clip(*r); 70 *g = clip(*g); 71 *b = clip(*b); 72} 73static void set_lum(float* r, float* g, float* b, float l) { 74 float diff = l - lum(*r,*g,*b); 75 *r += diff; 76 *g += diff; 77 *b += diff; 78 clip_color(r,g,b); 79} 80 81 82static void hue(float dr, float dg, float db, 83 float* sr, float* sg, float* sb) { 84 // Hue of Src, Saturation and Luminosity of Dst. 85 float R = *sr, 86 G = *sg, 87 B = *sb; 88 set_sat(&R,&G,&B, sat(dr,dg,db)); 89 set_lum(&R,&G,&B, lum(dr,dg,db)); 90 *sr = R; 91 *sg = G; 92 *sb = B; 93} 94 95static void saturation(float dr, float dg, float db, 96 float* sr, float* sg, float* sb) { 97 // Saturation of Src, Hue and Luminosity of Dst 98 float R = dr, 99 G = dg, 100 B = db; 101 set_sat(&R,&G,&B, sat(*sr,*sg,*sb)); 102 set_lum(&R,&G,&B, lum( dr, dg, db)); // This may seem redundant, but it is not. 103 *sr = R; 104 *sg = G; 105 *sb = B; 106} 107 108static void color(float dr, float dg, float db, 109 float* sr, float* sg, float* sb) { 110 // Hue and Saturation of Src, Luminosity of Dst. 111 float R = *sr, 112 G = *sg, 113 B = *sb; 114 set_lum(&R,&G,&B, lum(dr,dg,db)); 115 *sr = R; 116 *sg = G; 117 *sb = B; 118} 119 120static void luminosity(float dr, float dg, float db, 121 float* sr, float* sg, float* sb) { 122 // Luminosity of Src, Hue and Saturation of Dst. 123 float R = dr, 124 G = dg, 125 B = db; 126 set_lum(&R,&G,&B, lum(*sr,*sg,*sb)); 127 *sr = R; 128 *sg = G; 129 *sb = B; 130} 131 132static SkColor blend(SkColor dst, SkColor src, 133 void (*mode)(float,float,float, float*,float*,float*), 134 bool legacy) { 135 136 SkASSERT(SkColorGetA(dst) == 0xff 137 && SkColorGetA(src) == 0xff); // Not fundamental, just simplifying for this GM. 138 139 auto to_float = [&](SkColor c) { 140 if (legacy) { 141 return SkColor4f{ 142 SkColorGetR(c) * (1/255.0f), 143 SkColorGetG(c) * (1/255.0f), 144 SkColorGetB(c) * (1/255.0f), 145 1.0f, 146 }; 147 } 148 return SkColor4f::FromColor(c); 149 }; 150 151 SkColor4f d = to_float(dst), 152 s = to_float(src); 153 154 mode( d.fR, d.fG, d.fB, 155 &s.fR, &s.fG, &s.fB); 156 157 if (legacy) { 158 return SkColorSetRGB(s.fR * 255.0f + 0.5f, 159 s.fG * 255.0f + 0.5f, 160 s.fB * 255.0f + 0.5f); 161 } 162 return s.toSkColor(); 163} 164 165DEF_SIMPLE_GM(hsl, canvas, 600, 100) { 166 SkPaint label; 167 sk_tool_utils::set_portable_typeface(&label); 168 label.setAntiAlias(true); 169 170 const char* comment = "HSL blend modes are correct when you see no circles in the squares."; 171 canvas->drawText(comment, strlen(comment), 10,10, label); 172 173 // Just to keep things reaaaal simple, we'll only use opaque colors. 174 SkPaint bg, fg; 175 bg.setColor(0xff00ff00); // Fully-saturated bright green, H = 120°, S = 100%, L = 50%. 176 fg.setColor(0xff7f3f7f); // Partly-saturated dim magenta, H = 300°, S = ~33%, L = ~37%. 177 178 struct { 179 SkBlendMode mode; 180 void (*reference)(float,float,float, float*,float*,float*); 181 } tests[] = { 182 { SkBlendMode::kSrc, nullptr }, 183 { SkBlendMode::kDst, nullptr }, 184 { SkBlendMode::kHue, hue }, 185 { SkBlendMode::kSaturation, saturation }, 186 { SkBlendMode::kColor, color }, 187 { SkBlendMode::kLuminosity, luminosity }, 188 }; 189 bool legacy = !canvas->imageInfo().colorSpace(); 190 for (auto test : tests) { 191 canvas->drawRect({20,20,80,80}, bg); 192 193 fg.setBlendMode(test.mode); 194 canvas->drawRect({20,20,80,80}, fg); 195 196 if (test.reference) { 197 SkPaint ref; 198 ref.setColor(blend(bg.getColor(), fg.getColor(), test.reference, legacy)); 199 canvas->drawCircle(50,50, 20, ref); 200 } 201 202 const char* name = SkBlendMode_Name(test.mode); 203 canvas->drawText(name, strlen(name), 20,90, label); 204 205 canvas->translate(100,0); 206 } 207} 208