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Merge "Scrim opacity must satisfy GAR" into oc-dr1-dev

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am: f98facc3b8

Change-Id: I4c4eb814d8ea2152644665daf6fbd6eb28d81b06
This commit is contained in:
Lucas Dupin
2017-07-29 23:17:49 +00:00
committed by android-build-merger
parent e244efd69f f98facc3b8
commit 835f5e41de
3 changed files with 110 additions and 7 deletions
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57
core/java/com/android/internal/graphics/ColorUtils.java
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@@ -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);
}
}