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Commit 2285dd5a authored by Daniel Norman's avatar Daniel Norman
Browse files

fix(high contrast text): Fix the color calculation used in high contrast text 

- Treats more near-gray text as grayscale, which more-aggressively
  pushes text to pure white or black.
- Text treated as colorful will now never worsen the contrast by
  lightening already-dark or darkening already-light colors.

Also adds unit tests for this calculation.

NO_IFTTT=refactoring

Bug: 384793956
Flag: com.android.graphics.hwui.flags.high_contrast_text_inner_text_color
Test: See screenshot in b/384793956 comment24
Test: atest DrawTextFunctorTest
Change-Id: I9efa13f1741ac45e095e990952a45fdeaa9dce30
parent 0af50eb3

libs/hwui/Android.bp

+1 −0
Original line number Original line Diff line number Diff line
@@ -779,6 +779,7 @@ cc_test { 
        "tests/unit/CommonPoolTests.cpp",

        "tests/unit/CommonPoolTests.cpp",

        "tests/unit/DamageAccumulatorTests.cpp",

        "tests/unit/DamageAccumulatorTests.cpp",

        "tests/unit/DeferredLayerUpdaterTests.cpp",

        "tests/unit/DeferredLayerUpdaterTests.cpp",

        "tests/unit/DrawTextFunctorTest.cpp",

        "tests/unit/EglManagerTests.cpp",

        "tests/unit/EglManagerTests.cpp",

        "tests/unit/FatVectorTests.cpp",

        "tests/unit/FatVectorTests.cpp",

        "tests/unit/GraphicsStatsServiceTests.cpp",

        "tests/unit/GraphicsStatsServiceTests.cpp",

libs/hwui/hwui/DrawTextFunctor.h

+37 −17
Original line number Original line Diff line number Diff line
@@ -76,6 +76,41 @@ static void simplifyPaint(int color, Paint* paint) { 
    paint->setBlendMode(SkBlendMode::kSrcOver);

    paint->setBlendMode(SkBlendMode::kSrcOver);

}

}





namespace {



static bool shouldDarkenTextForHighContrast(const uirenderer::Lab& lab) {

    // LINT.IfChange(hct_darken)

    return lab.L <= 50;

    // LINT.ThenChange(/core/java/android/text/Layout.java:hct_darken)

}



}  // namespace



static void adjustHighContrastInnerTextColor(uirenderer::Lab* lab) {

    bool darken = shouldDarkenTextForHighContrast(*lab);

    bool isGrayscale = abs(lab->a) < 10 && abs(lab->b) < 10;

    if (isGrayscale) {

        // For near-grayscale text we first remove all color.

        lab->a = lab->b = 0;

        if (lab->L > 40 && lab->L < 60) {

            // Text near "middle gray" is pushed to a more contrasty gray.

            lab->L = darken ? 20 : 80;

        } else {

            // Other grayscale text is pushed completely white or black.

            lab->L = darken ? 0 : 100;

        }

    } else {

        // For color text we ensure the text is bright enough (for light text)

        // or dark enough (for dark text) to stand out against the background,

        // without touching the A and B components so we retain color.

        if (darken && lab->L > 20.f) {

            lab->L = 20.0f;

        } else if (!darken && lab->L < 90.f) {

            lab->L = 90.0f;

        }

    }

}



class DrawTextFunctor {

class DrawTextFunctor {

public:

public:

    /**

    /**
@@ -114,10 +149,8 @@ public: 
        if (CC_UNLIKELY(canvas->isHighContrastText() && paint.getAlpha() != 0)) {

        if (CC_UNLIKELY(canvas->isHighContrastText() && paint.getAlpha() != 0)) {

            // high contrast draw path

            // high contrast draw path

            int color = paint.getColor();

            int color = paint.getColor();

            // LINT.IfChange(hct_darken)

            uirenderer::Lab lab = uirenderer::sRGBToLab(color);

            uirenderer::Lab lab = uirenderer::sRGBToLab(color);

            bool darken = lab.L <= 50;

            bool darken = shouldDarkenTextForHighContrast(lab);

            // LINT.ThenChange(/core/java/android/text/Layout.java:hct_darken)





            // outline

            // outline

            gDrawTextBlobMode = DrawTextBlobMode::HctOutline;

            gDrawTextBlobMode = DrawTextBlobMode::HctOutline;
@@ -130,20 +163,7 @@ public: 
            gDrawTextBlobMode = DrawTextBlobMode::HctInner;

            gDrawTextBlobMode = DrawTextBlobMode::HctInner;

            Paint innerPaint(paint);

            Paint innerPaint(paint);

            if (flags::high_contrast_text_inner_text_color()) {

            if (flags::high_contrast_text_inner_text_color()) {

                // Preserve some color information while still ensuring sufficient contrast.

                adjustHighContrastInnerTextColor(&lab);

                // Thus we increase the lightness to make the color stand out against a black

                // background, and vice-versa. For grayscale, we retain some gray to indicate

                // states like disabled or to distinguish links.

                bool isGrayscale = abs(lab.a) < 1 && abs(lab.b) < 1;

                if (isGrayscale) {

                    if (darken) {

                        lab.L = lab.L < 40 ? 0 : 20;

                    } else {

                        lab.L = lab.L > 60 ? 100 : 80;

                    }

                } else {

                    lab.L = darken ? 20 : 90;

                }

                simplifyPaint(uirenderer::LabToSRGB(lab, SK_AlphaOPAQUE), &innerPaint);

                simplifyPaint(uirenderer::LabToSRGB(lab, SK_AlphaOPAQUE), &innerPaint);

            } else {

            } else {

                simplifyPaint(darken ? SK_ColorBLACK : SK_ColorWHITE, &innerPaint);

                simplifyPaint(darken ? SK_ColorBLACK : SK_ColorWHITE, &innerPaint);

libs/hwui/tests/unit/DrawTextFunctorTest.cpp

0 → 100644
+88 −0
Original line number Original line Diff line number Diff line 
/*

 * Copyright (C) 2025 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */



#include <gtest/gtest.h>



#include "hwui/DrawTextFunctor.h"



using namespace android;



namespace {



void testHighContrastInnerTextColor(float originalL, float originalA, float originalB,

                                    float expectedL, float expectedA, float expectedB) {

    uirenderer::Lab color = {originalL, originalA, originalB};

    adjustHighContrastInnerTextColor(&color);

    EXPECT_FLOAT_EQ(color.L, expectedL);

    EXPECT_FLOAT_EQ(color.a, expectedA);

    EXPECT_FLOAT_EQ(color.b, expectedB);

}



TEST(DrawTextFunctorTest, BlackUnaffected) {

    testHighContrastInnerTextColor(0, 0, 0, 0, 0, 0);

}



TEST(DrawTextFunctorTest, WhiteUnaffected) {

    testHighContrastInnerTextColor(100, 0, 0, 100, 0, 0);

}



TEST(DrawTextFunctorTest, DarkGrayPushedToWhite) {

    testHighContrastInnerTextColor(10, 0, 0, 0, 0, 0);

    testHighContrastInnerTextColor(20, 0, 0, 0, 0, 0);

}



TEST(DrawTextFunctorTest, LightGrayPushedToWhite) {

    testHighContrastInnerTextColor(80, 0, 0, 100, 0, 0);

    testHighContrastInnerTextColor(90, 0, 0, 100, 0, 0);

}



TEST(DrawTextFunctorTest, MiddleDarkGrayPushedToDarkGray) {

    testHighContrastInnerTextColor(41, 0, 0, 20, 0, 0);

    testHighContrastInnerTextColor(49, 0, 0, 20, 0, 0);

}



TEST(DrawTextFunctorTest, MiddleLightGrayPushedToLightGray) {

    testHighContrastInnerTextColor(51, 0, 0, 80, 0, 0);

    testHighContrastInnerTextColor(59, 0, 0, 80, 0, 0);

}



TEST(DrawTextFunctorTest, PaleColorTreatedAsGrayscaleAndPushedToWhite) {

    testHighContrastInnerTextColor(75, 5, -5, 100, 0, 0);

    testHighContrastInnerTextColor(85, -6, 8, 100, 0, 0);

}



TEST(DrawTextFunctorTest, PaleColorTreatedAsGrayscaleAndPushedToBlack) {

    testHighContrastInnerTextColor(25, 5, -5, 0, 0, 0);

    testHighContrastInnerTextColor(35, -6, 8, 0, 0, 0);

}



TEST(DrawTextFunctorTest, ColorfulColorIsLightened) {

    testHighContrastInnerTextColor(70, 100, -100, 90, 100, -100);

}



TEST(DrawTextFunctorTest, ColorfulLightColorIsUntouched) {

    testHighContrastInnerTextColor(95, 100, -100, 95, 100, -100);

}



TEST(DrawTextFunctorTest, ColorfulColorIsDarkened) {

    testHighContrastInnerTextColor(30, 100, -100, 20, 100, -100);

}



TEST(DrawTextFunctorTest, ColorfulDarkColorIsUntouched) {

    testHighContrastInnerTextColor(5, 100, -100, 5, 100, -100);

}



}  // namespace