Separate avatar colors from chat colors.

core-util/src/main/java/org/signal/core/util/ColorUtil.java

@@ -0,0 +1,43 @@
+package org.signal.core.util;
+
+import androidx.annotation.ColorInt;
+import androidx.annotation.FloatRange;
+
+public final class ColorUtil {
+
+  private ColorUtil() {}
+
+  public static int blendARGB(@ColorInt int color1,
+                              @ColorInt int color2,
+                              @FloatRange(from = 0.0, to = 1.0) float ratio)
+  {
+    final float inverseRatio = 1 - ratio;
+
+    float a = alpha(color1) * inverseRatio + alpha(color2) * ratio;
+    float r = red(color1)   * inverseRatio + red(color2)   * ratio;
+    float g = green(color1) * inverseRatio + green(color2) * ratio;
+    float b = blue(color1)  * inverseRatio + blue(color2)  * ratio;
+
+    return argb((int) a, (int) r, (int) g, (int) b);
+  }
+
+  private static int alpha(int color) {
+    return color >>> 24;
+  }
+
+  private static int red(int color) {
+    return (color >> 16) & 0xFF;
+  }
+
+  private static int green(int color) {
+    return (color >> 8) & 0xFF;
+  }
+
+  private static int blue(int color) {
+    return color & 0xFF;
+  }
+
+  private static int argb(int alpha, int red, int green, int blue) {
+    return (alpha << 24) | (red << 16) | (green << 8) | blue;
+  }
+}