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/gm.h"
9 #include "include/core/SkBlendMode.h"
10 #include "include/core/SkCanvas.h"
11 #include "include/core/SkColor.h"
12 #include "include/core/SkFont.h"
13 #include "include/core/SkPaint.h"
14 #include "include/core/SkTypeface.h"
15 #include "include/core/SkTypes.h"
16 #include "tools/Resources.h"
17 #include "tools/ToolUtils.h"
18
19 // Hue, Saturation, Color, and Luminosity blend modes are oddballs.
20 // They nominally convert their inputs to unpremul, then to HSL, then
21 // mix-and-match H,S,and L from Src and Dst, then convert back, then premul.
22 //
23 // In practice that's slow, so instead we pick the color with the correct
24 // Hue, and then (approximately) apply the other's Saturation and/or Luminosity.
25 // This isn't just an optimization... it's how the modes are specified.
26 //
27 // Each mode's name describes the Src H,S,L components to keep, taking the
28 // others from Dst, where Color == Hue + Saturation. Color and Luminosity
29 // are each other's complements; Hue and Saturation have no complement.
30 //
31 // All these modes were originally designed to operate on gamma-encoded values,
32 // and that's what everyone's used to seeing. It's unclear wehther they make
33 // any sense in a gamma-correct world. They certainly won't look at all similar.
34 //
35 // We have had many inconsistent implementations of these modes.
36 // This GM tries to demonstrate unambigously how they should work.
37 //
38 // To go along with our inconsistent implementations, there are two slightly
39 // inconsistent specifications of how to perform these blends,
40 // web: https://www.w3.org/TR/compositing-1/#blendingnonseparable
41 // KHR: https://www.khronos.org/registry/OpenGL/extensions/KHR/KHR_blend_equation_advanced.txt
42 // It looks like these are meant to be identical, but they disagree on at least ClipColor().
43 //
44 // I think the KHR version is just wrong... it produces values >1. So we use the web version.
45
min(float r,float g,float b)46 static float min(float r, float g, float b) { return std::min(r, std::min(g, b)); }
max(float r,float g,float b)47 static float max(float r, float g, float b) { return std::max(r, std::max(g, b)); }
48
sat(float r,float g,float b)49 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)50 static float lum(float r, float g, float b) { return r*0.30f + g*0.59f + b*0.11f; }
51
52 // The two SetSat() routines in the specs look different, but they're logically equivalent.
53 // Both map the minimum channel to 0, maximum to s, and scale the middle proportionately.
54 // 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)55 static void set_sat(float* r, float* g, float* b, float s) {
56 float mn = min(*r,*g,*b),
57 mx = max(*r,*g,*b);
58 auto channel = [=](float c) {
59 return mx == mn ? 0
60 : (c - mn) * s / (mx - mn);
61 };
62 *r = channel(*r);
63 *g = channel(*g);
64 *b = channel(*b);
65 }
clip_color(float * r,float * g,float * b)66 static void clip_color(float* r, float* g, float* b) {
67 float l = lum(*r,*g,*b),
68 mn = min(*r,*g,*b),
69 mx = max(*r,*g,*b);
70 auto clip = [=](float c) {
71 if (mn < 0) { c = l + (c - l) * ( l) / (l - mn); }
72 if (mx > 1) { c = l + (c - l) * (1 - l) / (mx - l); }
73 SkASSERT(-0.0001f < c); // This may end up very slightly negative...
74 SkASSERT( c <= 1);
75 return c;
76 };
77 *r = clip(*r);
78 *g = clip(*g);
79 *b = clip(*b);
80 }
set_lum(float * r,float * g,float * b,float l)81 static void set_lum(float* r, float* g, float* b, float l) {
82 float diff = l - lum(*r,*g,*b);
83 *r += diff;
84 *g += diff;
85 *b += diff;
86 clip_color(r,g,b);
87 }
88
89
hue(float dr,float dg,float db,float * sr,float * sg,float * sb)90 static void hue(float dr, float dg, float db,
91 float* sr, float* sg, float* sb) {
92 // Hue of Src, Saturation and Luminosity of Dst.
93 float R = *sr,
94 G = *sg,
95 B = *sb;
96 set_sat(&R,&G,&B, sat(dr,dg,db));
97 set_lum(&R,&G,&B, lum(dr,dg,db));
98 *sr = R;
99 *sg = G;
100 *sb = B;
101 }
102
saturation(float dr,float dg,float db,float * sr,float * sg,float * sb)103 static void saturation(float dr, float dg, float db,
104 float* sr, float* sg, float* sb) {
105 // Saturation of Src, Hue and Luminosity of Dst
106 float R = dr,
107 G = dg,
108 B = db;
109 set_sat(&R,&G,&B, sat(*sr,*sg,*sb));
110 set_lum(&R,&G,&B, lum( dr, dg, db)); // This may seem redundant, but it is not.
111 *sr = R;
112 *sg = G;
113 *sb = B;
114 }
115
color(float dr,float dg,float db,float * sr,float * sg,float * sb)116 static void color(float dr, float dg, float db,
117 float* sr, float* sg, float* sb) {
118 // Hue and Saturation of Src, Luminosity of Dst.
119 float R = *sr,
120 G = *sg,
121 B = *sb;
122 set_lum(&R,&G,&B, lum(dr,dg,db));
123 *sr = R;
124 *sg = G;
125 *sb = B;
126 }
127
luminosity(float dr,float dg,float db,float * sr,float * sg,float * sb)128 static void luminosity(float dr, float dg, float db,
129 float* sr, float* sg, float* sb) {
130 // Luminosity of Src, Hue and Saturation of Dst.
131 float R = dr,
132 G = dg,
133 B = db;
134 set_lum(&R,&G,&B, lum(*sr,*sg,*sb));
135 *sr = R;
136 *sg = G;
137 *sb = B;
138 }
139
blend(SkColor dst,SkColor src,void (* mode)(float,float,float,float *,float *,float *))140 static SkColor blend(SkColor dst, SkColor src,
141 void (*mode)(float,float,float, float*,float*,float*)) {
142
143 SkASSERT(SkColorGetA(dst) == 0xff
144 && SkColorGetA(src) == 0xff); // Not fundamental, just simplifying for this GM.
145
146 SkColor4f d = SkColor4f::FromColor(dst),
147 s = SkColor4f::FromColor(src);
148
149 mode( d.fR, d.fG, d.fB,
150 &s.fR, &s.fG, &s.fB);
151
152 return s.toSkColor();
153 }
154
155 DEF_SIMPLE_GM(hsl, canvas, 600, 100) {
156 SkPaint paint;
157 SkFont font(ToolUtils::create_portable_typeface());
158
159 const char* comment = "HSL blend modes are correct when you see no circles in the squares.";
160 canvas->drawString(comment, 10,10, font, paint);
161
162 // Just to keep things reaaaal simple, we'll only use opaque colors.
163 SkPaint bg, fg;
164 bg.setColor(0xff00ff00); // Fully-saturated bright green, H = 120°, S = 100%, L = 50%.
165 fg.setColor(0xff7f3f7f); // Partly-saturated dim magenta, H = 300°, S = ~33%, L = ~37%.
166
167 struct {
168 SkBlendMode mode;
169 void (*reference)(float,float,float, float*,float*,float*);
170 } tests[] = {
171 { SkBlendMode::kSrc, nullptr },
172 { SkBlendMode::kDst, nullptr },
173 { SkBlendMode::kHue, hue },
174 { SkBlendMode::kSaturation, saturation },
175 { SkBlendMode::kColor, color },
176 { SkBlendMode::kLuminosity, luminosity },
177 };
178 for (auto test : tests) {
179 canvas->drawRect({20,20,80,80}, bg);
180
181 fg.setBlendMode(test.mode);
182 canvas->drawRect({20,20,80,80}, fg);
183
184 if (test.reference) {
185 SkPaint ref;
186 ref.setColor(blend(bg.getColor(), fg.getColor(), test.reference));
187 canvas->drawCircle(50,50, 20, ref);
188 }
189
190 canvas->drawString(SkBlendMode_Name(test.mode), 20, 90, font, paint);
191
192 canvas->translate(100,0);
193 }
194 }
195
196 #include "include/effects/SkGradientShader.h"
197
198 // Trying to match sample images on https://www.w3.org/TR/compositing-1/#blendingnonseparable
199 //
make_grad(SkScalar width)200 static sk_sp<SkShader> make_grad(SkScalar width) {
201 SkColor colors[] = {
202 0xFF00CCCC, 0xFF0000CC, 0xFFCC00CC, 0xFFCC0000, 0xFFCCCC00, 0xFF00CC00,
203 };
204 SkPoint pts[] = {{0, 0}, {width, 0}};
205
206 return SkGradientShader::MakeLinear(pts, colors, nullptr, SK_ARRAY_COUNT(colors),
207 SkTileMode::kClamp);
208 }
209
210 DEF_SIMPLE_GM(HSL_duck, canvas, 1110, 620) {
211 auto src = GetResourceAsImage("images/ducky.png");
212 auto dst = make_grad(src->width());
213 SkRect r = SkRect::MakeIWH(src->width(), src->height());
214
215 canvas->translate(10, 50);
216 canvas->scale(0.5f, 0.5f);
217
218 const struct {
219 SkBlendMode fMode;
220 const char* fName;
221 } recs[] = {
222 { SkBlendMode::kHue, "Hue" },
223 { SkBlendMode::kSaturation, "Saturation" },
224 { SkBlendMode::kColor, "Color" },
225 { SkBlendMode::kLuminosity, "Luminosity" },
226 };
227
228 SkFont font;
229 font.setSize(40);
230 font.setEdging(SkFont::Edging::kAntiAlias);
231
232 canvas->save();
233 for (auto [_, name] : recs) {
234 canvas->drawSimpleText(name, strlen(name), SkTextEncoding::kUTF8, 150, -20,
235 font, SkPaint());
236 canvas->translate(r.width() + 10, 0);
237 }
238 canvas->restore();
239
240 for (SkScalar src_a : {1.0f, 0.5f}) {
241 canvas->save();
242 for (auto [mode, _] : recs) {
243 SkPaint p;
244 p.setShader(dst);
245 canvas->drawRect(r, p); // bg
246
247 p.setShader(nullptr);
248 p.setBlendMode(mode);
249 p.setAlphaf(src_a);
250 canvas->drawImageRect(src, r, SkSamplingOptions(), &p);
251
252 canvas->translate(r.width() + 10, 0);
253 }
254 SkString str;
255 str.printf("alpha %g", src_a);
256 canvas->drawSimpleText(str.c_str(), str.size(), SkTextEncoding::kUTF8, 10, r.height()/2,
257 font, SkPaint());
258
259 canvas->restore();
260 canvas->translate(0, r.height() + 10);
261 }
262 }
263
