Scrim opacity must satisfy GAR (9324aa92) · Commits · e / os / android_frameworks_base

core/java/com/android/internal/graphics/ColorUtils.java

+52 −5

Original line number	Diff line number	Diff line
		@@ -105,6 +105,31 @@ public final class ColorUtils {
		return Math.max(luminance1, luminance2) / Math.min(luminance1, luminance2);
		}

		/**
		* Calculates the minimum alpha value which can be applied to {@code background} so that would
		* have a contrast value of at least {@code minContrastRatio} when alpha blended to
		* {@code foreground}.
		*
		* @param foreground the foreground color
		* @param background the background color, opacity will be ignored
		* @param minContrastRatio the minimum contrast ratio
		* @return the alpha value in the range 0-255, or -1 if no value could be calculated
		*/
		public static int calculateMinimumBackgroundAlpha(@ColorInt int foreground,
		@ColorInt int background, float minContrastRatio) {
		// Ignore initial alpha that the background might have since this is
		// what we're trying to calculate.
		background = setAlphaComponent(background, 255);
		final int leastContrastyColor = setAlphaComponent(foreground, 255);
		return binaryAlphaSearch(foreground, background, minContrastRatio, (fg, bg, alpha) -> {
		int testBackground = blendARGB(leastContrastyColor, bg, alpha/255f);
		// Float rounding might set this alpha to something other that 255,
		// raising an exception in calculateContrast.
		testBackground = setAlphaComponent(testBackground, 255);
		return calculateContrast(fg, testBackground);
		});
		}

		/**
		* Calculates the minimum alpha value which can be applied to {@code foreground} so that would
		* have a contrast value of at least {@code minContrastRatio} when compared to
		@@ -122,14 +147,33 @@ public final class ColorUtils {
		+ Integer.toHexString(background));
		}

		ContrastCalculator contrastCalculator = (fg, bg, alpha) -> {
		int testForeground = setAlphaComponent(fg, alpha);
		return calculateContrast(testForeground, bg);
		};

		// First lets check that a fully opaque foreground has sufficient contrast
		int testForeground = setAlphaComponent(foreground, 255);
		double testRatio = calculateContrast(testForeground, background);
		double testRatio = contrastCalculator.calculateContrast(foreground, background, 255);
		if (testRatio < minContrastRatio) {
		// Fully opaque foreground does not have sufficient contrast, return error
		return -1;
		}
		foreground = setAlphaComponent(foreground, 255);
		return binaryAlphaSearch(foreground, background, minContrastRatio, contrastCalculator);
		}

		/**
		* Calculates the alpha value using binary search based on a given contrast evaluation function
		* and target contrast that needs to be satisfied.
		*
		* @param foreground the foreground color
		* @param background the opaque background color
		* @param minContrastRatio the minimum contrast ratio
		* @param calculator function that calculates contrast
		* @return the alpha value in the range 0-255, or -1 if no value could be calculated
		*/
		private static int binaryAlphaSearch(@ColorInt int foreground, @ColorInt int background,
		float minContrastRatio, ContrastCalculator calculator) {
		// Binary search to find a value with the minimum value which provides sufficient contrast
		int numIterations = 0;
		int minAlpha = 0;
		@@ -139,9 +183,8 @@ public final class ColorUtils {
		(maxAlpha - minAlpha) > MIN_ALPHA_SEARCH_PRECISION) {
		final int testAlpha = (minAlpha + maxAlpha) / 2;

		testForeground = setAlphaComponent(foreground, testAlpha);
		testRatio = calculateContrast(testForeground, background);

		final double testRatio = calculator.calculateContrast(foreground, background,
		testAlpha);
		if (testRatio < minContrastRatio) {
		minAlpha = testAlpha;
		} else {
		@@ -615,4 +658,8 @@ public final class ColorUtils {
		return result;
		}

		private interface ContrastCalculator {
		double calculateContrast(int foreground, int background, int alpha);
		}

		}
		No newline at end of file

packages/SystemUI/src/com/android/systemui/statusbar/phone/ScrimController.java

+17 −2

Original line number	Diff line number	Diff line
		@@ -37,6 +37,7 @@ import android.view.animation.PathInterpolator;
		import com.android.internal.colorextraction.ColorExtractor;
		import com.android.internal.colorextraction.ColorExtractor.GradientColors;
		import com.android.internal.colorextraction.ColorExtractor.OnColorsChangedListener;
		import com.android.internal.graphics.ColorUtils;
		import com.android.keyguard.KeyguardUpdateMonitor;
		import com.android.systemui.Dependency;
		import com.android.systemui.R;
		@@ -88,6 +89,7 @@ public class ScrimController implements ViewTreeObserver.OnPreDrawListener,
		private boolean mNeedsDrawableColorUpdate;

		protected float mScrimBehindAlpha;
		protected float mScrimBehindAlphaResValue;
		protected float mScrimBehindAlphaKeyguard = SCRIM_BEHIND_ALPHA_KEYGUARD;
		protected float mScrimBehindAlphaUnlocking = SCRIM_BEHIND_ALPHA_UNLOCKING;

		@@ -142,7 +144,10 @@ public class ScrimController implements ViewTreeObserver.OnPreDrawListener,
		mUnlockMethodCache = UnlockMethodCache.getInstance(context);
		mKeyguardUpdateMonitor = KeyguardUpdateMonitor.getInstance(context);
		mLightBarController = lightBarController;
		mScrimBehindAlpha = context.getResources().getFloat(R.dimen.scrim_behind_alpha);
		mScrimBehindAlphaResValue = context.getResources().getFloat(R.dimen.scrim_behind_alpha);
		// Scrim alpha is initially set to the value on the resource but might be changed
		// to make sure that text on top of it is legible.
		mScrimBehindAlpha = mScrimBehindAlphaResValue;

		mColorExtractor = Dependency.get(SysuiColorExtractor.class);
		mColorExtractor.addOnColorsChangedListener(this);
		@@ -342,20 +347,30 @@ public class ScrimController implements ViewTreeObserver.OnPreDrawListener,
		}

		protected void updateScrims() {
		// Make sure we have the right gradients
		// Make sure we have the right gradients and their opacities will satisfy GAR.
		if (mNeedsDrawableColorUpdate) {
		mNeedsDrawableColorUpdate = false;
		final GradientColors currentScrimColors;
		if (mKeyguardShowing) {
		// Always animate color changes if we're seeing the keyguard
		mScrimInFront.setColors(mLockColors, true /* animated */);
		mScrimBehind.setColors(mLockColors, true /* animated */);
		currentScrimColors = mLockColors;
		} else {
		// Only animate scrim color if the scrim view is actually visible
		boolean animateScrimInFront = mScrimInFront.getViewAlpha() != 0;
		boolean animateScrimBehind = mScrimBehind.getViewAlpha() != 0;
		mScrimInFront.setColors(mSystemColors, animateScrimInFront);
		mScrimBehind.setColors(mSystemColors, animateScrimBehind);
		currentScrimColors = mSystemColors;
		}

		// Calculate minimum scrim opacity for white or black text.
		int textColor = currentScrimColors.supportsDarkText() ? Color.BLACK : Color.WHITE;
		int mainColor = currentScrimColors.getMainColor();
		float minOpacity = ColorUtils.calculateMinimumBackgroundAlpha(textColor, mainColor,
		4.5f /* minimumContrast */) / 255f;
		mScrimBehindAlpha = Math.max(mScrimBehindAlphaResValue, minOpacity);
		mLightBarController.setScrimColor(mScrimInFront.getColors());
		}

tests/Internal/src/com/android/internal/graphics/ColorUtilsTest.java

0 → 100644

+41 −0

Original line number	Diff line number	Diff line
		/*
		* Copyright (C) 2017 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
		*/

		package com.android.internal.graphics;

		import android.graphics.Color;
		import android.support.test.filters.SmallTest;

		import org.junit.Test;

		import static org.junit.Assert.assertTrue;

		@SmallTest
		public class ColorUtilsTest {

		@Test
		public void calculateMinimumBackgroundAlpha_satisfiestContrast() {

		int alpha = ColorUtils.calculateMinimumBackgroundAlpha(Color.WHITE, Color.BLACK, 4.5f);
		assertTrue("Alpha doesn't need to be 255 to satisfy contrast", alpha < 255);

		int worstCase = ColorUtils.blendARGB(Color.WHITE, Color.BLACK, alpha/255f);
		worstCase = ColorUtils.setAlphaComponent(worstCase, 255);
		double contrast = ColorUtils.calculateContrast(Color.WHITE, worstCase);
		assertTrue("Blended color should satisfy contrast", contrast >= 4.5);

		}
		}