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- /*
- * Copyright 2017 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
- #include "gm/gm.h"
- #include "include/core/SkBlendMode.h"
- #include "include/core/SkCanvas.h"
- #include "include/core/SkColor.h"
- #include "include/core/SkFont.h"
- #include "include/core/SkPaint.h"
- #include "include/core/SkTypeface.h"
- #include "include/core/SkTypes.h"
- #include "tools/ToolUtils.h"
- // Hue, Saturation, Color, and Luminosity blend modes are oddballs.
- // They nominally convert their inputs to unpremul, then to HSL, then
- // mix-and-match H,S,and L from Src and Dst, then convert back, then premul.
- //
- // In practice that's slow, so instead we pick the color with the correct
- // Hue, and then (approximately) apply the other's Saturation and/or Luminosity.
- // This isn't just an optimization... it's how the modes are specified.
- //
- // Each mode's name describes the Src H,S,L components to keep, taking the
- // others from Dst, where Color == Hue + Saturation. Color and Luminosity
- // are each other's complements; Hue and Saturation have no complement.
- //
- // All these modes were originally designed to operate on gamma-encoded values,
- // and that's what everyone's used to seeing. It's unclear wehther they make
- // any sense in a gamma-correct world. They certainly won't look at all similar.
- //
- // We have had many inconsistent implementations of these modes.
- // This GM tries to demonstrate unambigously how they should work.
- //
- // To go along with our inconsistent implementations, there are two slightly
- // inconsistent specifications of how to perform these blends,
- // web: https://www.w3.org/TR/compositing-1/#blendingnonseparable
- // KHR: https://www.khronos.org/registry/OpenGL/extensions/KHR/KHR_blend_equation_advanced.txt
- // It looks like these are meant to be identical, but they disagree on at least ClipColor().
- //
- // I think the KHR version is just wrong... it produces values >1. So we use the web version.
- static float min(float r, float g, float b) { return SkTMin(r, SkTMin(g, b)); }
- static float max(float r, float g, float b) { return SkTMax(r, SkTMax(g, b)); }
- static float sat(float r, float g, float b) { return max(r,g,b) - min(r,g,b); }
- static float lum(float r, float g, float b) { return r*0.30f + g*0.59f + b*0.11f; }
- // The two SetSat() routines in the specs look different, but they're logically equivalent.
- // Both map the minimum channel to 0, maximum to s, and scale the middle proportionately.
- // The KHR version has done a better job at simplifying its math, so we use it here.
- static void set_sat(float* r, float* g, float* b, float s) {
- float mn = min(*r,*g,*b),
- mx = max(*r,*g,*b);
- auto channel = [=](float c) {
- return mx == mn ? 0
- : (c - mn) * s / (mx - mn);
- };
- *r = channel(*r);
- *g = channel(*g);
- *b = channel(*b);
- }
- static void clip_color(float* r, float* g, float* b) {
- float l = lum(*r,*g,*b),
- mn = min(*r,*g,*b),
- mx = max(*r,*g,*b);
- auto clip = [=](float c) {
- if (mn < 0) { c = l + (c - l) * ( l) / (l - mn); }
- if (mx > 1) { c = l + (c - l) * (1 - l) / (mx - l); }
- SkASSERT(-0.0001f < c); // This may end up very slightly negative...
- SkASSERT( c <= 1);
- return c;
- };
- *r = clip(*r);
- *g = clip(*g);
- *b = clip(*b);
- }
- static void set_lum(float* r, float* g, float* b, float l) {
- float diff = l - lum(*r,*g,*b);
- *r += diff;
- *g += diff;
- *b += diff;
- clip_color(r,g,b);
- }
- static void hue(float dr, float dg, float db,
- float* sr, float* sg, float* sb) {
- // Hue of Src, Saturation and Luminosity of Dst.
- float R = *sr,
- G = *sg,
- B = *sb;
- set_sat(&R,&G,&B, sat(dr,dg,db));
- set_lum(&R,&G,&B, lum(dr,dg,db));
- *sr = R;
- *sg = G;
- *sb = B;
- }
- static void saturation(float dr, float dg, float db,
- float* sr, float* sg, float* sb) {
- // Saturation of Src, Hue and Luminosity of Dst
- float R = dr,
- G = dg,
- B = db;
- set_sat(&R,&G,&B, sat(*sr,*sg,*sb));
- set_lum(&R,&G,&B, lum( dr, dg, db)); // This may seem redundant, but it is not.
- *sr = R;
- *sg = G;
- *sb = B;
- }
- static void color(float dr, float dg, float db,
- float* sr, float* sg, float* sb) {
- // Hue and Saturation of Src, Luminosity of Dst.
- float R = *sr,
- G = *sg,
- B = *sb;
- set_lum(&R,&G,&B, lum(dr,dg,db));
- *sr = R;
- *sg = G;
- *sb = B;
- }
- static void luminosity(float dr, float dg, float db,
- float* sr, float* sg, float* sb) {
- // Luminosity of Src, Hue and Saturation of Dst.
- float R = dr,
- G = dg,
- B = db;
- set_lum(&R,&G,&B, lum(*sr,*sg,*sb));
- *sr = R;
- *sg = G;
- *sb = B;
- }
- static SkColor blend(SkColor dst, SkColor src,
- void (*mode)(float,float,float, float*,float*,float*)) {
- SkASSERT(SkColorGetA(dst) == 0xff
- && SkColorGetA(src) == 0xff); // Not fundamental, just simplifying for this GM.
- SkColor4f d = SkColor4f::FromColor(dst),
- s = SkColor4f::FromColor(src);
- mode( d.fR, d.fG, d.fB,
- &s.fR, &s.fG, &s.fB);
- return s.toSkColor();
- }
- DEF_SIMPLE_GM(hsl, canvas, 600, 100) {
- SkPaint paint;
- SkFont font(ToolUtils::create_portable_typeface());
- const char* comment = "HSL blend modes are correct when you see no circles in the squares.";
- canvas->drawString(comment, 10,10, font, paint);
- // Just to keep things reaaaal simple, we'll only use opaque colors.
- SkPaint bg, fg;
- bg.setColor(0xff00ff00); // Fully-saturated bright green, H = 120°, S = 100%, L = 50%.
- fg.setColor(0xff7f3f7f); // Partly-saturated dim magenta, H = 300°, S = ~33%, L = ~37%.
- struct {
- SkBlendMode mode;
- void (*reference)(float,float,float, float*,float*,float*);
- } tests[] = {
- { SkBlendMode::kSrc, nullptr },
- { SkBlendMode::kDst, nullptr },
- { SkBlendMode::kHue, hue },
- { SkBlendMode::kSaturation, saturation },
- { SkBlendMode::kColor, color },
- { SkBlendMode::kLuminosity, luminosity },
- };
- for (auto test : tests) {
- canvas->drawRect({20,20,80,80}, bg);
- fg.setBlendMode(test.mode);
- canvas->drawRect({20,20,80,80}, fg);
- if (test.reference) {
- SkPaint ref;
- ref.setColor(blend(bg.getColor(), fg.getColor(), test.reference));
- canvas->drawCircle(50,50, 20, ref);
- }
- canvas->drawString(SkBlendMode_Name(test.mode), 20, 90, font, paint);
- canvas->translate(100,0);
- }
- }
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