Separating the draglayer alpha into multiple dimensions so that different animaitons

can run without affecting the other.

Bug: 79323355
Bug: 78880824
Change-Id: I11cb464ebdaad0a7f0a56d4bc4c3dff1d56da16b

src/com/android/launcher3/util/MultiValueAlpha.java

@@ -0,0 +1,101 @@
+/*
+ * Copyright (C) 2018 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.launcher3.util;
+
+import android.util.Property;
+import android.view.View;
+
+/**
+ * Utility class to handle separating a single value as a factor of multiple values
+ */
+public class MultiValueAlpha {
+
+    public static final Property<AlphaProperty, Float> VALUE =
+            new Property<AlphaProperty, Float>(Float.TYPE, "value") {
+
+                @Override
+                public Float get(AlphaProperty alphaProperty) {
+                    return alphaProperty.mValue;
+                }
+
+                @Override
+                public void set(AlphaProperty object, Float value) {
+                    object.setValue(value);
+                }
+            };
+
+    private final View mView;
+    private final AlphaProperty[] mMyProperties;
+
+    private int mValidMask;
+
+    public MultiValueAlpha(View view, int size) {
+        mView = view;
+        mMyProperties = new AlphaProperty[size];
+
+        mValidMask = 0;
+        for (int i = 0; i < size; i++) {
+            int myMask = 1 << i;
+            mValidMask |= myMask;
+            mMyProperties[i] = new AlphaProperty(myMask);
+        }
+    }
+
+    public AlphaProperty getProperty(int index) {
+        return mMyProperties[index];
+    }
+
+    public class AlphaProperty {
+
+        private final int mMyMask;
+
+        private float mValue = 1;
+        // Factor of all other alpha channels, only valid if mMyMask is present in mValidMask.
+        private float mOthers = 1;
+
+        AlphaProperty(int myMask) {
+            mMyMask = myMask;
+        }
+
+        public void setValue(float value) {
+            if (mValue == value) {
+                return;
+            }
+
+            if ((mValidMask & mMyMask) == 0) {
+                // Our cache value is not correct, recompute it.
+                mOthers = 1;
+                for (AlphaProperty prop : mMyProperties) {
+                    if (prop != this) {
+                        mOthers *= prop.mValue;
+                    }
+                }
+            }
+
+            // Since we have changed our value, all other caches except our own need to be
+            // recomputed. Change mValidMask to indicate the new valid caches (only our own).
+            mValidMask = mMyMask;
+            mValue = value;
+
+            mView.setAlpha(mOthers * mValue);
+        }
+
+        public float getValue() {
+            return mValue;
+        }
+    }
+}