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
min(float r,float g,float b)38 static float min(float r, float g, float b) { return SkTMin(r, SkTMin(g, b)); }
max(float r,float g,float b)39 static float max(float r, float g, float b) { return SkTMax(r, SkTMax(g, b)); }
40
sat(float r,float g,float b)41 static float sat(float r, float g, float b) { return max(r,g,b) - min(r,g,b); }
lum(float r,float g,float b)42 static 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.
set_sat(float * r,float * g,float * b,float s)47 static 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 }
clip_color(float * r,float * g,float * b)58 static 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 }
set_lum(float * r,float * g,float * b,float l)73 static 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
hue(float dr,float dg,float db,float * sr,float * sg,float * sb)82 static 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
saturation(float dr,float dg,float db,float * sr,float * sg,float * sb)95 static 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
color(float dr,float dg,float db,float * sr,float * sg,float * sb)108 static 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
luminosity(float dr,float dg,float db,float * sr,float * sg,float * sb)120 static 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
blend(SkColor dst,SkColor src,void (* mode)(float,float,float,float *,float *,float *),bool legacy)132 static 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
165 DEF_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